Sterrekunde

Is vog skadelik vir 'n Newtonse weerkaatser?

Is vog skadelik vir 'n Newtonse weerkaatser?


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Dit is dikwels koud buite, veral in die aand. As ek my Newtoniaanse weerkaatser terugneem in my huis, begin dit saamtrek.

Kan die water my teleskoop vernietig? of die spieëls? Moet ek dit skoonmaak?

My teleskoop is volledig geverf, maar ek is bang vir die skroewe. Skroewe roes dikwels.


Die buis self is nie so 'n groot probleem nie; vee dit net met 'n sagte lap af. Die skroewe moet vlekvrye staal wees, en die roes kan ook afgevee word.

Maar vog, wat humiesure van plante en stuifmeel bevat, sowel as vorm, beskadig die weerkaatsende oppervlaktes van spieëls. As dit duur is, laat dit buite of in 'n skuiling tot die volgende dag en bêre dit met die hoofspieël na onder. Moenie dit blootstel aan 'n temperatuurverandering van -10 tot + 20 ° C nie. Doen nie maak optiese oppervlaktes meganies skoon as u nie seker is oor die bedekking en die skoonmaakmiddels nie. As u die aluminiumoppervlak afvee, sal dit krap as dit geen beskermende laag het nie.

As dit 'n baie duur emmer is en u in 'n gebied is wat baie vog ervaar (waar ek woon, loop daar soms water van die buis af), oorweeg dan die verwarmers. Of probeer nog 'n dag :-)

Amateur-sterrekundige forums soos bv. cloudynights.com het baie meer inligting hieroor.

Hoop dit help.

Edit: ook: Hoe verwyder ek swam uit 'n teleskoopspieël?


Omgang met dou: dauwverwarmers, dauwskerms en meer

Deur: Alan MacRobert 15 Oktober 2006 2

Kry sulke artikels na u posbus gestuur

U kan maklik u eie dauwdop van skuimrubber maak. Sky & amp Teleskoop's Dennis diCicco het hierdie geskep deur 'n vel skuim met 'n mes en liniaal te sny, sy gesnyde rande aanmekaar te steek en met warm smeltlijm saam te voeg. Na dekades van eksperimentering met ander materiale, noem hy dit die beste dewap wat hy nog ooit gebruik het.

Hoe kan 'n teleskoop wat uit 'n warm huis geneem word, kouer word as die lug in u agterplaas? Deur hitte direk in die buitenste ruimte uit te straal, wat slegs enkele grade bo absolute nul is. Die resultaat? Dew op die omvang!

Die lens van hierdie refractor het 'n voldoende lang dauwkap (links) maar die Finderscope nie (regs), en dit sal dus vinnig dou word as dit onder die dauwpunt afkoel.

Oogstukke trek ook voordeel uit afskerming. Hierdie okulêre Edmund Scientific is voorsien van 'n oogbeker wat help om dou te voorkom en dwaallig te voorkom.

eerste bladsy van hierdie artikel.) 'n Bykomende voordeel is dat die dop ook afdwaallig wat in die teleskoop beland, verminder. Dit gesê, as u bekommerd is dat die pet dalk sal wees vignet die beeld (blokkeer 'n bietjie sterlig naby die rante van die gesigsveld), kan u die skuim sny sodat dit onder 'n effense hoek oopvlam. Slegs 'n openingshoek van 3 ° moet ten minste 'n gesigsveld van 3 ° moontlik maak.

Oogstukke is ook geneig tot dou. Warmte wat uit u gesig uitstraal, vertraag die dauwproses, maar vogtigheid van u oogappel en asem versnel dit. 'N Lang rubberoogskaal - die soort wat rondom die ooglens uitsteek - blokkeer nie net verdwaalde lig terwyl jy waarneem nie, maar dien ook as 'n miniatuurdoukop as jy wegkyk.


Inhoud

Newton se idee vir 'n weerkaatsende teleskoop was nie nuut nie. Galileo Galilei en Giovanni Francesco Sagredo het die gebruik van 'n spieël as die beeldvormende doelwit bespreek kort na die uitvinding van die brekings-teleskoop, [3] en ander, soos Niccolò Zucchi, beweer dat hulle al in 1616 met die idee geëksperimenteer het. [ 4] Newton het miskien selfs James Gregory se boek uit 1663 gelees Optica Promota wat die weerspieëling van teleskoopontwerpe met behulp van paraboliese spieëls beskryf het [5] ('n teleskoop wat Gregory suksesvol probeer bou het). [6]

Newton het sy weerkaatsende teleskoop gebou omdat hy vermoed dat dit sy teorie kan bewys dat wit lig uit 'n spektrum kleure bestaan. [7] Kleurvervorming (chromatiese aberrasie) was die primêre fout om teleskope van Newton se tyd te breek, en daar was baie teorieë oor wat dit veroorsaak het. Gedurende die middel van die 1660's met sy werk oor die teorie van kleur, het Newton tot die gevolgtrekking gekom dat hierdie defek veroorsaak is deur die lens van die brekende teleskoop wat dieselfde gedra as prisma waarmee hy geëksperimenteer het, en wit lig in 'n reënboog van kleure rondom helder sterrekundige voorwerpe gebreek het. [8] [9] As dit waar was, sou chromatiese afwyking uitgeskakel kon word deur 'n teleskoop te bou wat nie 'n lens gebruik het nie - 'n weerkaatsende teleskoop.

Laat in 1668 bou Isaac Newton sy eerste weerkaatsende teleskoop. Hy het 'n legering (spekulummetaal) van tin en koper gekies as die geskikste materiaal vir sy objektiewe spieël. Later het hy middele bedink om die spieël te vorm en te slyp en was hy moontlik die eerste wat 'n toonhoogte [10] gebruik het om die optiese oppervlak te poets. Hy het 'n sferiese vorm vir sy spieël gekies in plaas van 'n parabool om die konstruksie te vereenvoudig, alhoewel dit sferiese afwyking sou instel, sou dit steeds die chromatiese afwyking regstel. Hy voeg by sy weerkaatser wat die kenmerk is van die ontwerp van 'n Newtonse teleskoop, 'n sekondêre skuins gemonteerde spieël naby die fokus van die primêre spieël om die beeld in 'n hoek van 90 ° te weerspieël tot 'n okular wat aan die kant van die teleskoop gemonteer is. Met hierdie unieke toevoeging kon die beeld besigtig word met minimale belemmering van die objektiewe spieël. Hy het ook die buis, die berg en die toebehore gemaak. Newton se eerste weergawe het 'n primêre spieël-deursnee van 1,3 duim (33 mm) en 'n brandpuntverhouding van f / 5. [11] Hy vind dat die teleskoop sonder kleurvervorming werk en dat hy die vier Galilese mane van Jupiter en die halfmaanfase van die planeet Venus daarmee kan sien. Newton se vriend Isaac Barrow het 'n tweede teleskoop aan 'n klein groepie van die Royal Society of London getoon aan die einde van 1671. Hulle was so beïndruk daarmee dat hulle dit aan Charles II in Januarie 1672 getoon het. Newton is toegelaat as 'n genoot van die genootskap. in dieselfde jaar.

Soos Gregory voor hom, het Newton dit moeilik gevind om 'n effektiewe weerkaatser te konstrueer. Dit was moeilik om die spekulummetaal tot 'n gereelde kromming te slyp. Die oppervlak het ook vinnig aangetas deur die gevolglike lae weerkaatsingsvermoë van die spieël, en die klein grootte daarvan het beteken dat die uitsig deur die teleskoop baie swak was in vergelyking met hedendaagse vuurvaste. As gevolg van hierdie probleme met die konstruksie, is die Newtonse weerkaatsingsteleskoop aanvanklik nie algemeen gebruik nie. In 1721 wys John Hadley 'n baie verbeterde model aan die Royal Society. [12] Hadley het baie van die probleme om 'n paraboliese spieël te maak, opgelos. Sy Newtonian met 'n spieël-deursnee van 150 sentimeter het gunstig vergelyk met die groot teleskope van die dag. [13] Die grootte van weerkaatsende teleskope het daarna vinnig gegroei, met ontwerpe wat elke 50 jaar verdubbel in die primêre spieëldeursnee. [14]

  • Hulle is vry van chromatiese afwyking wat in brekende teleskope voorkom.
  • Newton-teleskope is gewoonlik goedkoper vir enige gegewe objektiewe deursnee (of diafragma) as vergelykbare teleskope van ander soorte.
  • Aangesien daar slegs een oppervlak is wat in 'n komplekse vorm gemaal en gepoleer moet word, is die algehele vervaardiging baie eenvoudiger as ander teleskoopontwerpe (Gregorianers, kassegraan en vroeë vuurvaste oppervlaktes het twee oppervlaktes wat nodig is om te bepaal. Latere achromatiese vuurvaste doelstellings het vier oppervlakke gehad moet gedink word).
  • 'N Kort brandpuntverhouding kan makliker verkry word, wat lei tot wyer gesigsveld.
  • Die okular is aan die bokant van die teleskoop geleë. Gekombineer met kort f-verhoudings kan dit 'n baie kompakter monteerstelsel moontlik maak, wat die koste verlaag en draagbaarheid verhoog.
  • Newtonianers, soos ander weerkaatsende teleskoopontwerpe wat paraboliese spieëls gebruik, ly aan koma, 'n afwaartse as van die as wat die beeld na binne en na die optiese as laat opvlam (sterre na die rand van die gesigsveld kry 'n "komeetagtige" vorm) . Hierdie fakkel is nul op die as, en is lineêr met toenemende veldhoek en omgekeerd eweredig aan die vierkant van die spieëlfokusverhouding (die spieëlfokale lengte gedeel deur die spieëldeursnee). Die formule vir derde orde tangensiële koma is 3θ / 16F², waar θ die hoek van die as af tot die beeld in radiale is en F die brandpuntverhouding is. Newtonians met 'n brandpuntverhouding van f / 6 of laer (byvoorbeeld f / 5) word beskou as toenemend ernstige koma vir visuele of fotografiese gebruik. [15] Primêre spieëls met 'n lae brandpuntverhouding kan gekombineer word met lense wat vir koma regstel om die beeldskerpte oor die veld te verhoog. [16]
  • Newtonians het 'n sentrale obstruksie as gevolg van die sekondêre spieël in die ligpad. Hierdie obstruksie en ook die afbreekpunte wat veroorsaak word deur die steunstruktuur (genoem die spinnekop) van die sekondêre spieël verminder die kontras. Visueel kan hierdie effekte verminder word deur 'n twee of drie-been geboë spin te gebruik. Dit verminder die diffraksie-sywaartse intensiteit met 'n faktor van ongeveer vier en help om die kontras van die beeld te verbeter, met die moontlike boete dat sirkelspinnekoppe meer geneig is tot vibrasie deur winde.
  • Vir draagbare Newtonianers kan kollimasie 'n probleem wees. Die primêre en sekondêre toestand kan buite pas kom van die skokke wat verband hou met vervoer en hantering. Dit beteken dat die teleskoop miskien elke keer wanneer dit opgestel word, weer moet gerig (gekollimeer) word. Ander ontwerpe soos vuurvaste en katadioptriese (spesifiek Maksutov-kassegraine) het 'n vaste kollimasie.
  • Die fokusvlak is op 'n asimmetriese punt en aan die bokant van die optiese buissamestelling. Vir visuele waarneming, veral op ekwatoriale teleskoopbevestigings, [17] kan buisoriëntasie die okularis in 'n baie slegte kykposisie plaas, en groter teleskope benodig lere of ondersteuningstrukture om toegang daartoe te kry. [18] Sommige ontwerpe bied meganismes om die oculairbevestiging of die hele buisstuk beter te draai. Vir navorsingsteleskope moet rekening gehou word met die balansering van baie swaar instrumente wat op hierdie fokus gemonteer is.

Jones-Bird Edit

'N Jones-Bird-reflektorteleskoop (soms Bird-Jones genoem) is 'n spieëllens (katadioptriese) variasie op die tradisionele Newtonse ontwerp wat in die amateurteleskoopmark verkoop word. Die ontwerp gebruik 'n sferiese primêre spieël in die plek van 'n paraboliese, met sferiese afwykings wat reggestel word deur 'n korrigeringslens van die subopening [19], gewoonlik binne die fokusbuis of voor die sekondêre spieël. Hierdie ontwerp verminder die grootte en koste van die teleskoop met 'n korter totale lengte van die teleskoopbuis (met die korridor wat die brandpuntlengte verleng in 'n "telefoto" -uitleg), gekombineer met 'n goedkoper sferiese spieël. Daar is opgemerk dat kommersieel vervaardigde weergawes van hierdie ontwerp opties gekompromitteer word as gevolg van die moeilikheid om 'n korrek gevormde sub-diafragma-regstelling in 'n teleskoop te vervaardig wat op die goedkoop einde van die teleskoopmark gerig is. [20]


Is vog skadelik vir 'n Newtonse weerkaatser? - Sterrekunde

Dauwskerm, lenskap, of wat jy dit ook al noem, die meeste teleskope het dit nodig. Dauw is snags 'n ernstige probleem. Die daling en die humiditeit van die nag is die belangrikste faktore in vogvorming, en sommige gebiede en klimate is dus slegter as ander. Wanneer lug begin afkoel, verloor dit sy vermoë om vog te hou en kondensasie begin vorm. As die humiditeit hoog is, word die dauwpunt by 'n hoër temperatuur bereik. As daar dou op die oogpunt, regter of spieël van u teleskoop vorm, kan dit die nagwaarneming beëindig, dus moet voorkoming van dauwe ernstig opgeneem word.

Brekende en katadioptriese (CAT) teleskope het die neiging om dou op hul voorlense te versamel, wat immers meestal hemelwaarts gerig is. 'N Afdekkap kan hierdie probleem vir refraktore en RTT's verminder, maar nie uitskakel nie.

'N Bindwerk-reflektor moet gehul word om dou van die primêre spieël te hou. Die lang buis van 'n konvensionele Newtonse weerkaatser dien gewoonlik as 'n effektiewe douskerm en Newtonianers word selde met 'n aanvullende kap gesien. Ditto vir Cassegrain-weerkaatsers en Vixen CAT's met 'n oop buis, hoewel daar wel dou op die sekondêre spieël is en in toestande van ernstige dou, selfs op primêre spieëls. Ek het dou op die primêre spieël van 'n 6 & quot Newtonse weerkaatser met 'n naatlose aluminiumbuis verdig. Die hoofbuis was baie langer as enige praktiese dauwskerm vir breek- en CAT-teleskope.

Refraktors kom dikwels met 'n ingeskroefde of uittrekbare lenskap, maar CAT's kom selde voor. As u kat nie 'n voldoende dauwskerm het nie, moet u dit koop. Gewoonlik is 'n toepaslike douskerm by die vervaardiger van die teleskoop beskikbaar, maar indien nie, is dit beskikbaar op die na-mark. Afdekkap / douskerms is gewoonlik styf (metaal of hard plastiek) of buigbaar (ABS plastiek of iets soortgelyks). Albei soorte is ongeveer ewe effektief om die vorming van dou te vertraag, maar buigsame douskerms is baie makliker om op te berg of te vervoer en word gewoonlik verkies vir draagbare teleskope.

Celestron en Vixen verkoop buigsame douskerms wat vir hul CAT's gemaak is. Orion bied hul soortgelyke & quotFlexishields & quot aan vir 'n wye verskeidenheid Orion en ander CAT's. Dit is gemaak van buigsame ABS-plastiek en draai om die voorkant van die teleskoop om 'n kap te vorm wat deur 'n klittenbandstrook vasgemaak word. Dit is 'n gerieflike ontwerp wat goed werk. Vir opberging lê die dauwskerm plat of kan dit om die hoofbuis van die omvang gewikkel word. Orion bied hul Flexishield vir 90mm (3,5 & quot), 102mm (4 & quot), 127mm (5 & quot), 150mm (6 & quot), 203mm (8 & quot), 235mm (9.25 & quot), 254mm (10 & quot) en 280mm (11 & quot) teleskope. Feitlik almal op die Sterrekunde en fotografie aanlyn personeel wat 'n CAT besit, gebruik hierdie tipe doudskerm. Dit is ook effektiewe sonskerms vir diegene wat hul CAT's gebruik vir landelike besigtiging of as tele-kameralense. Die koste is gewoonlik matig, gewoonlik ongeveer $ 25 - $ 35 aanlyn vir 'n 8 & quot SCT.

Kendrick bied 'n bietjie minder elegante buigsame douskerms in verskillende groottes om teleskope van 3,5 tot 14 duim te pas. Ek het een daarvan op my Meade ETX-90 gebruik en dit het goed gewerk. Kendrick verkoop ook 'n douverwyderaarstelsel, 'n draagbare elektriese verwarmingstelsel wat ontwerp is om die vorming van dou te voorkom. Dit is beskikbaar in groottes vir die meeste teleskope, okulêre en selfs die Telrad-rooi kolvinder.

Orion (Dew Zapper), Astrozap, Vixen en ander verkoop ook draagbare, battery-aangedrewe (DC) verwarmingsstelsels om dauwvorming op die voorste lense, vingeromvang en oogkykers te voorkom. Dit is beskikbaar in die vorm van enkele, met klittenband aangehegte, verwarmingsbande in lengtes wat ontwerp is om by die meeste teleskope in te pas, of meerkanaals verwarmingsstelsels wat tot vier teleskope, soekbestek of okulare gelyktydig kan beskerm. Elke verwarmingsband het sy eie reostaat om die temperatuur onafhanklik te beheer. Verhitstroke van verskillende lengtes is apart beskikbaar. Sulke toestelle word gewoonlik aangedryf deur 'n motorbattery via 'n sigaretaanstekerprop of 'n draagbare herlaaibare 12-volt-battery. Vixen's Dew Heater 2, 'n 665 mm lange hittestrook, word voorsien van 'n handige batterypakket wat agt D-selbatterye vir ongeveer $ 135 gebruik (Woodland Hills Telescope, 2010).

'N Ander toestel wat ontwerp is om dauwvorming te bekamp, ​​is die verhitte douskerm, soos dié van Astrozap. Dit is gewoonlik baie soos die hierbo beskryf buigsame douskerms, maar voeg 'n dun rubberstrook aan die binnekant van die douskerm by. Onder hierdie strook is verwarmingselemente wat die korrigeringslens van die teleskoop warm maak om dit bo die dauwpunt te hou. 'N Koord verbind die verhitte douskerm met sy beheerder, wat op sy beurt via 'n sigarettenaansteker aan 'n 12 volt GS-kragbron gekoppel is. Die dauwskerm hou die ligte verwarmde lug naby u omvanglens. Dit word beweer dat dit die afvoer van die battery verminder wat nodig is om u omvang douvry te hou in vergelyking met die gebruik van 'n aparte douverwarmerstrook. Aan die ander kant kan warm lugstrome binne die douskerm vorm, wat nie gebeur met afsonderlike verwarmingsbande wat buite om die hoofbuis van die omvang agter 'n konvensionele douskerm toegedraai word nie. Astrozap maak verhitte douskerms vir die omvang van 3,5 & quot tot 16 & quot.

Die verhitte douskerm is miskien die elegantste manier om douvorming te bekamp. Dit is egter waarskynlik die duurste. Byvoorbeeld, 'n Astrozap-verhitte dauwskerm vir 'n 8 & quot SCT verkoop aanlyn vir ongeveer $ 75, die Astrozap-tweekanaal-, vier-uitset-verwarmerbeheerder is ongeveer $ 105 en 'n Celestron 7 amp-uur kragtenk kos ongeveer $ 65 (alles in 2010 dollar).

'N goedkoper, aktiewe doubeheermetode is 'n battery aangedrewe (draadlose), luglug haardroër, wat gebruik word saam met 'n gewone douskerm. 'N Lae watt-model is die beste vir teleskoopgebruik (anders as om hare te droog!). Maak seker dat die model wat u kies, 'n lae hitte-instelling het, aangesien u nie meer warmlugstrome wil skep of u regter meer wil verhit as wat nodig is nie. Ek het dit suksesvol besit en gebruik. Op die een of ander manier is dit noodsaaklik vir waarnemers om dauwvorming op optiese oppervlaktes te voorkom. Hoe gesofistikeerd en duur u stelsel is, hang af van u beursie en u tipiese waarnemingsomstandighede.


Hoe om u teleskoop te versorg

Wil u seker maak dat u waarnemingstoerusting u goed dien? Hier is hoe u u teleskoop skoon en droog moet hou.

Hierdie kompetisie is nou gesluit

Gepubliseer: 5 Augustus 2020 om 11:18

As u die teleskoop skoon hou, is voorkoming beter as genesing. Om te keer dat u teleskoop vies word, is verkieslik om die gevolge daarna uit te sorteer. Dit is onmoontlik om 'n omvang vir altyd in perfekte toestand te hou, tensy u skuldig is aan die ergste misdaad teen sterrekunde en dit nog nooit toegedraai het nie!

Met verloop van tyd sal daar stof en vuiligheid op die oppervlaktes van die optika van u teleskoop opbou en 'n bietjie sagte sorg sal nodig wees om dit weer tot volle glorie te bring. Dit is 'n besondere probleem met Newtoniaanse omvang en die groot Dobsonians met 'n oop buis, of vakwerk, ontwerp.

U moet egter die optika net skoonmaak as dit regtig nodig is. 'N Klein hoeveelheid stof berokken immers nie die uitsig nie, terwyl die skoonmaak van die spieël of lens veel meer skade kan berokken.

Lees ons gids oor voorbereiding vir die nuwe sterrekunde-seisoen vir meer inligting oor die skoonmaak van teleskope en toerusting.

Volledige skoonmaakgidse:

Hoe om u teleskoop te beskerm

As dit nie gebruik word nie, moet alle optika beskerm word met lens-, okularis- en vinkdekkies of kappies. As u kan, bêre u teleskoop in 'n stof- en vuilvrye omgewing.

'N Motorhuis of tuinhuisie kan prakties wees, maar nie noodwendig die beste vir u omvang nie. 'N Binnekas wat skoon gehou kan word, is die beste opsie.

Selfs as die lensdop aan is, kan stof binne die bestek val. Bêre dus u omvang met die weerkaatsende kant van die hoofspieël na onder om dit te vermy.

Wat toebehore soos okulariste betref, sal dit in 'n tip-top toestand bly as dit in verseëlbare plastiek bokse of sakke gebêre word.

Hoe om u teleskoop skoon te maak

Selfs nadat u al hierdie advies gevolg het, sal daar 'n tyd wees dat u voel dat dit skoon is. Maak eers seker dat die area waarin u skoonmaak, skoon is.

Moenie dit snags buite doen nie en moet nooit 'n rooi lamp gebruik nie, want u sal nie die stof kan sien nie. 'N Skoon kombuistafel onder 'n helder lamp vir eenvormige beligting is 'n goeie plek om dit te doen.

Die volgende toerusting is nuttig om 'n teleskoop skoon te maak:

  • Lens skoonmaakweefsels
  • Mikrovesellens skoonmaakdoek
  • Katoenknoppies
  • Lugblaaslamp (sonder borsel)
  • Alkohol-gebaseerde skoonmaakvloeistof

Ten opsigte van die finale item word asetoon skoonmaakvloeistof nie aanbeveel nie, want dit kan verf en plastiek van die rand van die lens oplos. En gebruik nooit naellak verwyderaar nie.

Die skoonmaak van 'n spieël in 'n weerkaatsende teleskoop is baie eenvoudig - dit kan skoongemaak word in 'n opwasbak gevul met warm kraanwater en 'n paar druppels afwasmiddel.

Na skoonmaak, spoel dit met gedistilleerde water (beskikbaar by aptekers) en laat dit droog word.

Moenie die berg vergeet nie. Baie mense gebruik 'n spuitmiddel, soos WD-40, om van die ou vet op die ratte ontslae te raak en die dele teen vog te beskerm.

Vervang enige vet wat u uithaal deur wit litiumvet wat by fietswinkels beskikbaar is.

'N Ander prosedure word gebruik om 'n lens in 'n refractor of 'n teleskoop skoon te maak met beide spieëls en lense - sien die stappe hierbo.

Met ultra-skoon optika in u teleskoop, sal u die perfekte uitsig lank geniet.

Hoe om 'n teleskooplens skoon te maak

Verwyder stofdeeltjies

As u lens vuil is, moet u stofdeeltjies verwyder voordat u dit skoonmaak. Gebruik 'n lugblaas om die losste deeltjies saggies op te blaas.

Gebruik nie 'n lughouer of asem nie, want dit sal vog op die lens waai, wat die oorblywende deeltjies kan laat vassit.

Al die stof moet skoongemaak word voordat u dit skoonmaak, anders versprei u bloot die stof rondom die lens, wat dit moeiliker maak om skoon te maak. U loop ook die gevaar om die lens te krap as u afvee.

Vee af met alkohol skoonmaakvloeistof

Vog nou 'n doek met alkohol skoonmaakvloeistof. Vee die lens saggies in 'n sirkelbeweging van die middel na die rand af, met so min druk as moontlik.

Nadat u die lens met 'n sneesdoek afgevee het, gooi die sneesdoek weg en kies 'n vars, skoon een vir u volgende vee - u wil geen deeltjies oor die lens vee nie.

Probeer om die lens per ongeluk nie tydens hierdie proses aan te raak nie, maar maak die vingermerke noukeurig skoon.

Beskerm die kante

Die rand van die lens is 'n gebied om op te let. Moenie hier te veel vloeistof gebruik nie, want dit kan deur die kapillêre werking in die lenselemente kruip.

U kan ook vind dat daar water kolle op die lens is as gevolg van dou of atmosferiese kondensasie.

Slegs in hierdie stadium kan hulle verwyder word deur saggies daarop asem te haal en met 'n skoon weefsel af te vee.

Dit is omdat suiwer alkohol skoonmaakvloeistof nie water kolle sonder vog sal oplos nie, wat in hierdie geval uit u asem kom.

Hoe om u teleskoop op te berg

Teleskope is presiese stukke uitrusting, en die doel van die 'gelukkige teleskoop'-speletjie is om 'n veilige tuiste te vind wat vog en vog, stampe en knalle, stof en vuil, hoë temperatuur swaai, spinnekoppe en insekte vermy.

U kan die solder, 'n ekstra slaapkamer, 'n afdak of dalk die motorhuis oorweeg. Dit is alles algemene plekke wat deur amateursterrekundiges regoor die wêreld gebruik word.

Waar u ook al u hou, moet u ook nadink oor die voorsorgmaatreëls wat u moet tref om u omvang in die beste werkende toestand te hou.

Een van die maklikste voorsorgmaatreëls is om die omvang met 'n laken (of selfs beter, 'n omslaglaag) te bedek, gevolg deur iets waterdig om die vog buite te hou. Dit is veral belangrik as u dit ten volle saamstel tussen die waarnemingsessies, eerder as om dit terug te plaas na 'n opbergdoos.

Met 'n bietjie tou kan u selfs insekte wat u ook wil beplan om 'n huis te bou, buite rekening hou.

Maak ook seker dat u alle deksels en deksels vervang, want dit hou die optika en binnekant vry van vog en stof.

Alles in ag genome is 'n droë binnekas 'n goeie plek. U moet nog steeds u omvang met 'n laken bedek en die doppies aantrek, maar die atmosfeer is nie so korrosief soos elders nie.

Dit is natuurlik miskien nie prakties nie. As u byvoorbeeld groot is en dit bo hou, kan die vooruitsig om dit buite te kry, genoeg wees om u uit te stel. Die enigste ding wat erger is as 'n verwoeste omvang, is iets wat so goed gestoor word dat dit nooit gebruik word nie.

Een plek waar u u toerusting beslis nie moet hou nie, is 'n serre. Teleskope hou nie van plekke met baie vog nie, en ook nie die temperatuur-uiterstes wat hier gevind kan word nie.

Alternatiewelik, as u die ruimte, die tyd en die begroting het, kan u altyd die gesprek van u omgewing word en 'n toegewyde ruimte vir u omvang bou: u eie sterrewag.

Gevare wat u moet vermy as u u teleskoop bêre

Dauwe op die optika kan op sy beste 'n nagwaarneming verwoes deur die uitsig op te ruim. In die ergste geval sal dit waarskynlik allerhande nare bring wat lensbedekkings kan beskadig.

Onaktiwiteit

As u bloot 'n lang tyd 'n ruimte ongestoord laat, kan dit probleme veroorsaak. Dit kan onder meer toelaat dat swaartekrag die vet wat oor die ratte sit, herverdeel. Dit laat bewegende dele vatbaar vir oormatige slytasie en skade.

Mense en troeteldiere

Van al die dinge wat die lewe van 'n teleskoop ernstig kan verkort, is u naaste die ergste oortreders. Moet nooit 'n teleskoop op enige plek verlaat waar dit omgestamp kan word, teen 'n muur geslaan kan word, as 'n kapstok gebruik word of deur die kat geklim kan word nie.

Temperatuur

Warmer is nie noodwendig beter nie - hoë temperature kan u omvang beskadig, die vet op ratte verdamp of die gom wat die lense vashou, verswak.

Water

Nat of klam bergingstoestande doen u omvang nie goed nie: u sal binnekort roes op al die gewrigte begin vorm. Selfs as u u omvang eenvoudig in sy geval wegpak sonder om dit eers volledig te droog, vra u vir 'n swamaanval op die lense.

Maak u eie teleskoopberging

Teleskoopkas

As u vind dat die opbergtas wat by u bestek gekom het te dun is (of inderdaad, as dit nie by een kom nie), kan u dit oorweeg om dit op maat te maak. U kan 'n wonderwerk skep wat pas by u omvang - of u stoorplek - presies, en voeg ook ekstra afdelings vir u bykomstighede by. Die enigste nadeel is dat u u omvang na elke sessie moet skei.

Teleskoop-driepoot op wiel

Sommige driepote kan opvallend swaar stukke kit wees, en dit kan moeilik wees om dit te dra, met die kans om in dinge te slaan of selfs jou rug te seer. Dus, hoe gaan dit met die probleem deur 'n driepoot met intrekwiele te hê? Solank die grond nie te hobbelig is nie, kan u nou met gemak saam gly.

Hierdie gids verskyn oorspronklik in die uitgawes van Oktober 2010 en September 2012BBC Sky at Night Magazine.


Die klassieke Cassegrain: bewese uitnemendheid

Die meeste teleskoopgebruikers ken die Schmidt-Cassegrain-ontwerp, 'n katadioptriese kortbuis wat baie gewild is onder astronomie- en astrofotografie-liefhebbers. Maar hoewel die meeste mense bekend is met die naam Schmidt, ontwyk die oorsprong van die Cassegrain-deel van die naam die Schmidt-kamera, wat deur Bernhard Schmidt uitgevind is, baie. Die ontwerp van die Cassegrain-weerkaatser word gewoonlik toegeskryf aan Laurent Cassegrain, 'n Franse priester, wat dit iewers in die vroeë 1670's ontwikkel het. Dit is interessant om daarop te let dat dit nie Cassegrain self was wat oor hierdie ontwerp gepubliseer het nie, maar 'n sekere M. de Bercé, wat die ontwerp beskryf het in 'n wetenskaplike tydskrif wat deur die beroemde Franse dokter, Jean-Baptiste Denys, gepubliseer is. Dit is waarskynlik die rede waarom iemand eers in die middel van die 1700's probeer het om een ​​te bou. Die onwilligheid om die Cassegrain-ontwerp te implementeer, spruit miskien uit die feit dat dit nog nie 'n beproefde ontwerp was nie, in vergelyking met die goed gepubliseerde en maklik beskikbaar weerkaatsende teleskoopontwerpe wat deur Gregory en Newton gemaak is, wat laasgenoemde uiteindelik die gewildste styl van weerkaatser.

Om die onduidelikheid van die Cassegrain-ontwerp te bevorder, is die feit dat ander noemenswaardige teleskoopbouers die ontwerp om die een of ander rede sterk gekritiseer het. Die bekendste persoon wat sy vermeende gebreke aangehaal het, is die Nederlandse sterrekundige Christiaan Huygens, wat dit miskien gedoen het ter ondersteuning van die meer gewilde Newtonse reflektorontwerp (Huygens was self net vertroud met open buis-refraktore). Alhoewel ons dalk nooit die rede weet waarom sommige sterrekundiges van die tydperk Cassegrains-ontwerp verwerp het nie, was die impak van hierdie negatiwiteit voldoende om die gewildheid onder waarnemers te demp.

Eers in die 1940's is Cassegrain se ontwerp weer aan die lig gebring, maar slegs as onderdeel van 'n nuwe ontwerp wat Barnard Schmidt se regterplaat opgeneem het. Hierdie nuwe ontwerp, wat in die vroeë veertigerjare deur James Gilbert Baker en sy span by die Mount Wilson Observatory ontwikkel is, het uiteindelik bekend geword as die Schmidt-Cassegrain-reflektor, 'n lang fokuspunt-ontwerp, maar met 'n kort optiese buis, wat dit baie gewild gemaak het. as gevolg van die opening van groot openings, maar tog die draagbaarheid van 'n kortbuisreflector. Dit is die ontwerp wat maatskappye soos Meade en Celestron in staat gestel het om hulself as première-teleskoopkleinhandelaars te vestig, aangesien die ontwerp selfs gemaklike astronomie-entoesiaste bemagtig met 'n kompakte, maar hoogwaardige instrument om hemelliggame te bekyk en te fotografeer.

Ondanks die gewildheid daarvan, het Schmidt-Cassegrains 'n aantal probleme waarmee waarnemers voortdurend te kampe het en kan dit hoofpyn wees veral as die teleskoop as 'n suiwer astrograaf gebruik word. Een belangrike voorbeeld is die feit dat as die temperatuurverskil binne die geslote buis en die buitekant beduidend is, dou en vog op die regterplaat kan ophoop. Dit dwing die SC-gebruiker gewoonlik om op dauwskerms of plaatverwarmers te belê, wat slegs bydra tot die totale gewig van die teleskoop. 'N Mens moet ook batterykrag aan sommige van hierdie toestelle voorsien, en as jy dit in 'n afgeleë gebied waarneem, sal dit beperk word tot die beperkte kragbegroting wat jy dalk vir die aand se waarnemingsessie voorberei het.

'N Ander probleem met Schmidt-Cassegrains is die feit dat die meganisme om te fokus behels dat die primêre spieël heen en weer moet beweeg op 'n onderstel wat aan die fokuser gekoppel is. Dit kan lei tot situasies waarin die fokus fokus dat die spieël wankel of flop, as gevolg van die skroefdraad se verskuiwing op die onderstel terwyl u fokus, wat die kollimasie en optiese presisie beïnvloed. Nog 'n probleem wat verband hou met hierdie fokusontwerp, is die feit dat die montering van 'n taamlike swaar diagonale + okular, of kamera of ander beeldtoestelle op die trekbuis ook 'n invloed op die botsing kan hê, in ag genome die verbinding van die buis met die onderstel wat wieg. die primêre spieël. Dit vererger die spieëlflop of -skof verder terwyl u fokus.

Baie gebruikers van Schmidt-Cassegrain is gewoond daaraan om oplossings of hacks te vind om die probleme en probleme wat verband hou met die ontwerp te hanteer. Daar is egter sommige wat probeer het om maniere te vind om hierdie probleem uit die weg te ruim deur miskien 'n nuwe reflektorontwerp te ontwikkel. Sommige teleskoopontwerpers het egter net 'n meer pragmatiese oplossing bedink - waarom sou die Cassegrain nie herbou word soos dit deur die uitvinder ontwerp is nie? Die resultaat van hierdie strewe is die Klassieke Cassegrain. Hierdie moderne aanpak van die klassieke Cassegrain-ontwerp boots nie net die oorspronklike konsep vir hierdie toestel na nie, maar bevat kritieke verbeterings en moderne tegnieke wat die akkuraatheid en bruikbaarheid daarvan verder verbeter. Ons kyk nou na die komende 8 ”OTA van die Classic Cassegrain-ontwerp wat binnekort in die ASC-voorraad beskikbaar sal wees.

Met die eerste oogopslag na die ontwerp is die duidelikste verskil tussen 'n Classic Cassegrain (CC) en 'n Schmidt-Cassegrain (SC) die gebrek aan 'n regterplaat voor die buis. Die meeste SC's hou die sekondêre spieël op sy plek via die regterplaat, maar in die geval van 'n CC word 'n tradisionele 4-vinger-presisie-gemonteerde spinnekop gebruik wat aan die Newtoniaanse ontwerp herinner. The lack of the corrector plate immediately eliminates the perennial problem of moisture build-up on the plate itself. As for the issue of the primary mirror dewing up, the OTA is slightly longer (f/12) than that of a standard 8” SC, and thus dewing on the primary isn’t a big issue—the tube itself acts as its dew shield. The spider holds a secondary mirror mount that is 68mm across, which may seem large, but obscuration of the primary mirror in terms of diameter is 34%, but in terms of mirror area this only corresponds to only 12%. The long focal length of 2400mm (f/12) seems quite extended, but is in fact “folded” into an optical tube just 25″ long, still within the range of compactness as other SCs or Maks.

Another feature that’s immediately noticeable once you peer into the tube is the addition of internal baffling or ribs along the length of the OTA. Most telescope tubes rely on either a matte black finish, or perhaps some black felt material to reduce light scattering. However, it has been observed that baffles are one of the most efficient ways to subdue light scatter and suppressing stray light that would otherwise wash out images and produce less-than-optimal contrast. The upcoming ASC 8” CC has 11 baffles running the entire length of the OTA, effectively minimizing the light scatter. There have been reports of people attempting or successfully removing these baffles from CC’s, in the hopes of increasing the light-gathering properties of their tubes. An owner is indeed free to do this as a choice, but it must be stressed that these baffles were installed in the tube for a reason, and its removal might actually degrade image quality rather than improve it. More light does not necessarily equate to better image.

Moving on to the focuser, the CC features a very robust linear bearing Crayford focuser that can accommodate up to 2” diameter attachments. The focusing knob has a welcome two-dial dual speed setup, allowing coarse and fine focus adjustment. The fine focus dial is calibrated to move in 1/10 th finer scales of the coarse focus knob, which is a necessity during high-magnification imaging and observation. The robust linear bearing design allows for a bit of extra weight for such things as draw tube extensions to hold monochrome cameras and/or filter wheels, with no worry of slippage. The CC comes with one 2″-length extension ring and two 1″-length extension ring, and a 1.25” adapter. The threads of these accessories are blackened to prevent glare. It’s important to note that since the mechanism doesn’t involve any movement of the primary mirror, as such in an SC, then the stationary nature of the primary and secondary mirrors only lends more to ensuring a quality image. Speaking of the mirrors themselves, both the 200mm primary mirror and the secondary are made from an enhanced aluminium coating with an overcoat layer of thermally stable quartz. This assures that the mirrors won’t exhibit image shift or mirror flop like the Pyrex ones in a typical SC or Maksutov, plus it provides for a shorter cooling time. These mirrors offer 96% reflectivity.

The total weight of the OTA is at 18.2 lbs (8.25 kg), which means that you still have around 11 pounds worth of accessories that you can still attach on the OTA to support 30-40 lb mounts such as an iOptron iEQ45 Pro. For attachments, you are provided with two dovetail finder scope bases, giving you the freedom to mount an optional Orion finder scope on either side of the focuser, or to mount a small guide scope and finder scope simultaneously, a setup ideal if you’re constantly switching between Alt-Az and EQ orientation and require attaching two different finder setups.

In summary, what you get is a telescope with good optics, quartz mirrors, added light baffles for improved contrast, shorter cooling time and all this for a great price. If you’d like to dive into high-magnification sessions, using an 8mm eyepiece for the CC will yield 300x of useful magnification, which makes this an excellent instrument for such a compact setup, yet it is also perfect for wider-field sessions with very minimal distortions up to the edge of the viewing field. All in all, truly an exciting telescope to have and use, a true classic, as designed and conceptualized by Laurent Cassegrain over 300 years ago.


Is moisture harmful to a Newtonian Reflector? - Sterrekunde

Imagine that you're out with the scope. It's been warm during the day - a little humid. But you've let your scope cool down as the sunset progressed to twilight and now it's dark and everything is in thermodynamic equilibrium (the telescope, optics and the ambient air temperature are all equal.) Then you notice that the front corrector plate on your Schmidt-Cassegrain is fogging up - "dewing" as amateur astronomers call it. Why is that? Everything is at the same temperature, so what's causing the condensation to form?

The answer lies in the cold depths of space.

The most common equipment hassle that observers face at night is water on the telescope, which comes as a surprise to newcomers who expect things to stay dry in clear weather. Unfortunately, the steadiest, sharpest telescopic views are often had under precisely the atmospheric conditions that cause dew to form. At the eyepiece you first notice dim stars and galaxies becoming harder to see, then bright stars develop fuzzy halos -- and a check with the flashlight reveals wet haze coating the optics. In severe cases the whole telescope may be soaked. Wiping never helps (and can hurt the multi-coatings!) more water condenses the moment you stop. At this point many observers pack up, defeated.

However, you can keep your lenses and mirrors crystal clear in even the heaviest dewing conditions. You just need to understand the enemy and take effective countermeasures.

Dew does not "fall" from the sky. It condenses from the surrounding air onto any object that's colder than the air's dew point. The dew point (or saturation line), often mentioned in weather broadcasts, depends on both temperature and humidity. When the humidity is 100 percent, the dew point is the same as the air temperature. At lower humidity, the dew point is below the air temperature. If it's below freezing, you get frost instead of liquid water.

An example of dew physics occurs when you take a bottle out of the refrigerator. If the bottle is colder than the air's dew point, it drips with condensation. Your telescope is the bottle.

Great! So dewing occurs when the temperature of the Schmidt-Cassegrain corrector plate falls below the air temperature by some amount. How's this possible? Isn't everything is in thermal equilibrium - the scope, the air. ??

There are three methods of heat transfer - conduction, convection, and radiation. The key here is radiation. The telescope, if pointed at clear sky, is in "thermal contact" by radiation with a very cold source. At wavelengths where the atmosphere is transparent, it's only 'seeing' the 3 degree Kelvin background radiation of space.

An example I like to use is that when I leave my car on the street overnight, I can find dew or frost on the front and back windows but not on the side windows. The same effect is responsible. The side windows are vertical, so they 'see' my house, the house across the street or trees, etc. - all of which are relatively warm and radiate infrared radiation. The front and back windows are sloped, so they are looking at the cold sky and cool well below the side windows.

The first line of defense against dew, therefore, is to shield your optics from as much exposure to the night sky as is feasible. The traditional dewcap extending beyond a refractor's lens often serves this purpose well enough to keep the lens dry. The longer the dewcap, the more likely it is to work. One of the nice things about a Newtonian reflector is that its entire tube acts as a dewcap to shield the mirror in the bottom. An open-tube reflector, however, needs a cloth shroud around its open framework to gain this benefit. The cloth itself, of course, will get wet on its sky-facing side.

The worst dew problems appear on exposed parts that are thin (or have low heat capacity) and rapidly radiate away their warmth. Schmidt-Cassegrain corrector plates are notorious for dewing so are Telrad sights with their exposed glass. A dew shield is reportedly the first accessory that Schmidt-Cassegrain owners most often come back to buy.

Orion makes a dew cap to fit most telescopes.

You can easily make your own. A piece of tough 5/8-inch foam rubber, the kind sold in sporting-goods stores to go under sleeping bags, makes a dew shield that's cheap, durable, and very lightweight. The foam is an excellent insulator, for maximum effectiveness. If you're concerned that the cap might vignette the image (block some starlight near the edges of the field of view), you can cut the foam so it flares open at a very slight angle. A 3 opening angle should allow a 3 unvignetted field of view.

As a rule of thumb, a dewcap should be at least 1 times as long as the aperture is wide. A side benefit is that the cap also cuts down on stray light getting into the telescope.

Eyepieces too are prone to dewing. Warm radiation from your face slows the process, but humidity from your eyeball and breath speeds it up. A tall rubber eyecup, the kind that extends above the eye lens all around, not only blocks stray light while you're observing but acts as a miniature dewcap when you're looking away.

The same principle works on large scales. Early on a clear morning, have you noticed grass in the middle of a field white with frost or dew while grass near a tree has none? The tree is a giant dewcap, and it can work for you too. If you'll be looking at only one part of the sky, it's nice to have trees around and behind you. Not just your telescope but your charts and accessories will stay dry longer.

Trees also reduce wind problems, but a slight breeze is a good thing. Radiational cooling is slow and inefficient compared to heat transfer with the surrounding air, so even the mildest breeze will keep your telescope nearly up to air temperature.

The Heat is On

There will be times and places where none of this is enough. You then have no choice but to warm your optics, usually electrically.

A 120-volt hair dryer, used gently from a distance so it doesn't overheat the glass and warp it, will blow off dew for perhaps five minutes. Then you have to use it again. And again. A 12-volt auto windshield defogger gun is somewhat less effective. A better way is to apply a little heat continuously. Heated dewcaps that run off a 12-volt battery are advertised in Sky and Telescope magazine, or with just a little electrical know-how you can make an anti-dew heater to any size, shape, and specification you want. Orion makes the "Dew Zapper" that many have found very successful.

Warmed optics can have unexpected benefits. Dew works its first subtle evils before you notice anything. The late Walter Scott Houston used electric warmers on both the objective and eyepiece holder of his 4-inch refractor. When he turned off the power, the telescope could lose a whole magnitude of light grasp before the objective actually looked dewy.

"Even on nights when dewing is not noticeable," Houston wrote, "the star images seem better with the heaters on than without them!" This may be because, contrary to what you might think, gentle heating keeps a telescope close to the temperature of the surrounding air. After all, the whole idea is to stop it from growing colder than the air.

Not-So-Cold Storage

The most destructive dewing happens when a telescope is in storage. No telescope should be closed up and put away until it is thoroughly dry. Water with nowhere to escape, or condensation that forms and evaporates repeatedly in a sealed environment over months and years, may attack optical coatings and ultimately etch the glass itself.

How, you may ask, does water get into an airtight space that was dry when you sealed it? The answer is it was there all along. Air contains water vapor, and if your telescope gets colder than what the dew point was when the air was sealed in, water will condense. This is why so many puzzled telescope owners discover water stains on the inside surfaces of their corrector plates and refractor lenses.

Several approaches can prevent this. Don't move a sealed telescope from warm to cold storage. In fact, sealing may be a bad idea altogether. The best telescope covering is cloth, which will "breathe." It keeps dust off but lets water vapor out. And you might want to leave the eyepiece holder covered only with cloth, just enough to keep dust and spiders out.

The worst problems occur when a warm front of humid air blows in after cold weather, as often happens in early spring. Everything cold gets drenched. A cloth wrap may be the best defense here too it will greatly reduce the amount of humid air that can flow over cold parts.

The usual advice is to store a telescope at the outdoor temperature to minimize tube currents when you set it up. But this old rule may need modification. Keeping the telescope a little warmer will tend to thwart condensation. An enclosed porch or attached garage may provide the extra few degrees you need. And really long-term storage should probably be inside your living space. Never leave a telescope in a damp basement or garage or, as a rule of thumb, any place where tools grow rusty.

You can take active countermeasures too. A 4- or 7-watt light bulb inserted into a blanketed telescope makes a nice low-power heater. Position it just below or right next to the glass, or else you may merely drive off water from other parts of the tube that will condense onto the cold optics. Running the bulb continuously will cost about a dollar per watt per year. You might turn it on only in the damp season, or attach it to a humidistat switch.

Silica gel desiccant will dehumidify the air in a tightly sealed enclosure. I keep a -pound bag in plastic webbing attached to the inside of one of the tube caps of my 12.5-inch reflector. Every month or two when the bag's indicator slip turns from blue to pink, I heat the bag in a toaster oven in my observatory to drive off the collected moisture. The more tightly you seal your tube or storage case, the less often you'll have to do this.

Water can be an insidious enemy for astronomers, but a little
knowledge will keep it permanently at bay.

Adapted from "Dealing With Dew," By Alan MacRobert, an Associate Editor of Sky & Telescope magazine and an avid backyard astronomer.

A Dew Cap for Your Telescope
astro-tom.com

With the change of seasons, you may notice dew forming on the front lens or corrector plate of your telescope or binoculars. Have you seen the symptoms? Dim stars become hard to see, bright stars get a halo around them, and your observations come to an end for the evening.

Dew forms when your optics cool to a temperature below the dew point where water will condense out of the air onto any surface colder than this temperature. What happens is that while you and your optics are typically looking at cold, black space, the surrounding air is warmed by residual heat of the land around you. Dew condenses out of the surrounding air like the moisture that condenses on the outside of a glass of ice water.

Dew doesn't damage a telescope, but it can sure ruin a night of observing. I'm sure that you know that just wiping the dew off with a soft cloth can scratch your optics, so a better solution is to understand how to prevent its formation in the first place.

A dew cap for a refractor or Schmidt-Cassegrain telescope should be at least 1.5 times longer than the diameter of the front of the telescope. A tough 5/8" piece of closed cell foam, like the kind used for sleeping bag backpacking pads, is ideal, especially the black pads. They're lightweight and durable. This material can be found at most sporting goods stores and is easy to cut cleanly with a utility knife. Take the pad and wrap it around the telescope tube, then add 1-2 inches for room for attachment and cut the pad. Use a full length strip of self-sticking Velcro to secure the dew cap together. If you use a black pad, your new dew cap will have the added benefit of effectively blocking stray light out of the optics.

If you're concerned about vignetting, make your dew cap so that it flares open approximately 3 , which will be sufficient for wide-angle eyepieces.

To store the dew cap, slide it down the telescope tube, which will make it convenient to use and protect the tube from dings.

One nice thing about a Newtonian Reflector is that the entire tube acts as a dew cap. The only way to get rid of dew in this case is to use a small hair dryer to get it off of the main mirror. When not looking at something, point the scope downwards to the horizon so that you're not pointing the optics at cold space.

Dew can also form on eyepieces, but the heat from your face helps to keep it at bay, and at the same time moisture from your breath and eye is making the situation worse! Warming an eyepiece in a pocket for a few moments is usually enough to remove dew and keep it at bay for a while.

By the way, a dew cap is usually the first accessory that an owner of a Schmidt-Cassegrain telescope purchases. But now you can save yourself a lot of money and make one yourself.


Reflector/Refractor equivalence formula

I decided to post this in the Refractor forum, too, to get people's input here. Jarad Schiffer, in the thread "Long focus Newtonian Vs refractor" in the Reflector forum wrote the oft quoted formula that to determine a Newtonian's performance to an equivalent refractor, do this .

Reflector Primary - Secondary = Refractor Primary Equivalent

I noted Jon Isaacs many times writing that the real difference is more like

Reflector Primary - 1" = Refractor Primary Equivalent

I propose, to quantify Jon's assertion, perhaps the formula should look like this .

Reflector Primary - (0.5 * Secondary) = Refractor Primary Equivalent

As one got above a 40% obstruction, this formula might not apply, but I'm not as concerned about astrographs functioning as visual instruments

I take the example of the Celestron Omni XLT 150, which has a 150mm objective with a 46.5mm CO. Now according to Jarad's formula, that should make the Omni XLT equivalent to a 103.5mm refractor for planetary performance. But in my proposed reworked formula, the "Refractor Equivalence" of the Omni XLT should be a 126.75mm scope. Now, people may say this is wishful thinking, and I cannot say with any certainty that it isn't, but it would be nice to see how an Omni XLT 150 compares with 4" ED, 110mm ED, and 120mm ED (as well as the equivalent achromatic) scopes. I own neither the 110 nor 120mm ED scopes, nor any achromat, though there's a STRONG temptation for me to buy the XLT and compare it to my 102mm ED scope. According to Jarad's formula, it should still surpass it, but really, just barely, and the planetary performance should really be about the same. Stay tuned, but anyone else wishing to evaluate my recalculation of that old Reflector

Refractor Equivalence formula is more than welcome to educate me and the rest of the CN Brotherhood.

For the record, the Omni XLT delivers the same number of photons to your retina as a 142.6mm refractor -- (Pi * r squared of the Primary) minus (Pi * r squared of the Central Obstruction). Obviously, those photons are maligned a bit for human vision by the CO, but how much is the question.

#2 Eddgie

The old "Primary minus Secondary obstruction) offers at very best, a very crude approximation of how the instruments will perform visually, and only visually.

And if you want to make the comparison and not get an approximation, try using Abberator 3.0 to generate your own MTF plots. It is easy to use.

The MTF plot tells the truth about how much contrast is lost.

Here is an MTF for an 8" Newtonian with 23% obstruction (Dashed red) vs a perfect 8" aperture (solid red) and a perfect 6" unobstructed aperture. I have included the spider vanes (which means the scope started with a 21% secondary mirror and I added 2% to that for the spider vanes).

The Green line is for a perfect 6" Aperture with the assumption that the color correction is perfect (which is rarely the case by the way, but I am assuming a best case.

As you can see, the 8" scope offers contrast that is on par with the perfect 6" aperture for larger details, but for the smallest details, the reflector pulls away, still showing small detail after the perfect 6" aperture has run out of steam.

So, no need to apply coarse formulas when you can plot it pretty closely and know a more accurate picture.

Abberator will only allow you to plot one scope.

I plot the larger instrument, then hand draw the curve for the smaller perfect instrument.

In this case, the 6" has .75 of the maximum spatial response of the 8" scope, so it is plotted to the .75 index on the frequency line at the bottom of the chart.

Also, MTF ignores the higher illumination you get out of the larger aperture for a given exit pupil. A brighter image helps the eye better see the lowest contrast detail on the target.


The development of Telescope

People have contributed on growth and development of telescope creating, none more substantially than William Herschel.

Born in Hanover, Germany, Herschel decided in The united kingdom in 1757, where he became contemplating astronomy and soon after (1776) switched his attention to telescopes. Operating totally by hand, at first as an amateur, he practiced and created their strategy on a lot of telescopes into the design of Newton and discovered simple tips to figure the mirrors better than had some of their predecessors. He performed the polishing within the traditional manner, with all the mirror on top, and used a sweeping, circular stroke for parabolizing.

Herschel himself started to design, which is known as the Herschelian kind, which was originally proposed by French scientist LeMaire, in 1728. Within the design, the mirror itself is tilted so your image is projected to one region of the open end of the pipe, in which it could be analyzed in comfort, utilizing the observer’s back once again to the thing, and minus the introduction of an additional expression.

This second feature ended up being of tremendous importance in the days of speculum, whenever 40 percent for the light has been consumed in undergoing one reflection. Of less significance, but nonetheless gainful, was the elimination associated with the harmful diffraction effects from the secondary mirror. But unless an adequately high focal ratio ended up being selected, astigmatic photos lead through the interest of this mirror. Which launched another problem the lengthening associated with pipe meant putting the observer at an awkward level.|

In 1789, Herschel completed their biggest reflector, regarding the tilted-mirror kind, that has been installed at Slough, near Windsor. The speculum ended up being four feet in diameter, with a focal period of 40 foot. It absolutely was about 3½” dense, and weighed about 2,100 weight. A more elaborate and ingenious trestlework was created to carry the observer.|

This excellent mirror was surpassed using completion in 1845 associated with the largest of most specula, one six legs in diameter and 54 feet in focal length, by the Irish astronomer, Lord Rosse. It was an important step in telescope making.The metal disk was almost 6″ thick, and weighed about 8,380 pounds when cast. Rosse’s gigantic tool was mounted at Parsonstown, Ireland.|

As agent associated with the prices Herschel recharged for his reflectors, a Newtonian style of 6½-inch diameter and seven legs focal size offered for 100 guineas (30 guineas for the optical parts). Another 8.8-inch Newtonian, 10-foot focus, is priced at 200 to 300 guineas. Herschel informed buying two mirrors because of this second tool (which most likely makes up the adjustable price) to ensure you can use it applied whilst the other was being re polished!

His abilities were not confined to the creating of good specula he, in addition made his own eyepieces, some of which have been really remarkable. Their regular sources was to the utilization of magnifications of approximately 7,000 on their 6½-inch reflector which occasioned some speculation and controversy within the list of ranking English astronomers, but their claim have been warranted by the development, relatively recently, of some very small eyepieces produced by Herschel.

Among their results at Slough, W. H. Steavenson discovered some eyepieces ranging in focal length from about 1/16″ downward. The littlest among these have been analyzed in a microfocometer, and discovered to own a focal amount of 0.011″. It was bi-convex, about 1/45″ in diameter, and 1/90″ in thickness.

It was tried out on a 6-inch refractor, and performed since creditably as its energy would permit, but its industry because instrument was only about 20 moments of arc in diameter. If Herschel in fact used this eye-piece on his 85.2″ focal size reflector, it might have provided magnification of 7,668.|

William Herschel had been certainly significant factor to mighty task of telescope generating.

You Are Going To Soon Be Gazing At The Stars Through Your Own Telescopes|


5 inch vs 6 inch reflector?

Would there be a significant difference between a 5 inch and 6 reflector?

I'm talking about the Orion Starseeker II 130mm & the Orion Starblast 6i to be specific

#2 AcesDJD

This will depend on your light pollution situation as well as what you're looking to observe. With things like nebulas and galaxies every inch counts, although if you're in a white zone and most red zone areas the inch more won't help much. I would consider even a bigger scope if you're going to be observing from your house. I took some getting used to, but I no longer have much trouble carting around a 10 inch SCT. I have no knowledge of the specific scopes you're referring to, so someone else chime in if you know the difference.

#3 izar187

With both on hand, eventually you will see that 6" will out resolve 5", just a bit, in all targets.

Not at first glance necessarily.

But in an apples to apples comparisons, of similar types of scopes, at the same magnification. it is apparent.

#4 gene 4181

#5 tigerroach

If you are considering an upgrade from a 5", the 6" wouldn't really be worth it. I would recommend going to 8" to get a nice, noticeable boost in resolution and light-gathering power.

If you are deciding between a 5" and a 6", yes the 6" will show a little more. As posted above there will be a difference but it might not be noticeable right off.

Edited by tigerroach, 08 October 2014 - 07:30 AM.

#6 gene 4181

Edited by gene 4181, 08 October 2014 - 02:53 PM.

#7 MarcusE

I use a 5" mak-cass and a 6" mak-Newtonian from the same location in an urban area. I did not think there would be much noticeable difference. However, in my experience, I can see more with the 6" scope. Both scopes have tracking. The difference for me is one is grab and go, the other, not so much.

#8 Hesiod

StarseekerII has a quite frail mount (I'll go for Celestron version wich have a slightly sturdier tripod. Better color scheme for Orion however), while the Starblast mount is solid albeit quite low: most people have to put the Starblast on a table/rock/crate or sit down in the grass.

The Starseeker mount also requires an external powersource (it can work with 8AAs*, but they usually do not last very long, so on the mid-term a "powertank" is rewarding money-wise).

*math tells that 10 rechargeable AA could make the mount work, but I did not tried in this case you would need a 10-slot powerpack with the right jack (cheap stuff which can be found in electrical equipment shop, bricolage shop or even those shops selling scaled models of planes, cars, etc. )

#9 Jon Isaacs

There is a lot of good information in this thread. Here's my two cents.

- Optically, the 6 inch scope has the advantage over the 130mm, you will see more, not a lot more but noticeably more.

- The big differences between these two scopes are the mounts and quality of the parts..

The 130mm Starseeker is essentially the same scope as the Nexstar 130SLT, I had one for a while. The telescope itself is good. The mount way undersized for this scope, vibration is a constant problem and the drives can fail. The OTA hits the mount at higher elevations. The dovetail is mounted directly to the OTA rather than with tube rings, this adds to the vibration issues and I could actually see the OTA sag with heavy eyepieces. The plastic focuser is adequate but makes accurate focusing difficult. In my mind, the scope is a good one, the mount is a decent entry level mount but overloaded with this particular scope. nie goed nie. It's not a robust, long term combination.

The Starblast 6i, is a different animal.. It has the simplicity and robustness of the Dobsonian, it has the Intelliscope to help guide you, it has tube rings to make for a stable mounting of the OTA.. The focuser is plastic but usable.. The difficulty with the Starblast is that it's a table top mount. Table top mounts are not user friendly, they seem like a good idea but in practice, they are woeful.. a telescope really needs a rock-solid, sturdy mount, otherwise vibration and instability are issues. A folding table is simply out of the question.. A park bench table seems reasonable.. It's stable enough but when you sit on the seat, that causes problems but the big problem is the limited access to the eyepiece. Another issue is that if you accidentally move the scope while trying to get to the eyepiece, the Intelliscope is no longer aligned.

So.. my question for Addi319: What attracts you to these two scopes? Why these two rather than a standard Dobsonian?

#10 hottr6

I did a review of a Meade N6 6" f/5 and Sky-Watcher 127mm f/5 some years ago here on CN. cannot find it right now. Both were fitted with 2" Crayford focusers. The Meade needed at least a CG5-class GEM, the Sky-Watcher (SW) was happiest on a much lighter Vixen Polaris GEM.

The 6" shows a lot more than the 5" on DSOs. The difference in views of globs was quite surprising.

The 6" Meade OTA is a heavy beast at around 14lbs the SW OTA when similarly configured weighed around 10lbs. This is mainly due to the steel tube used by Meade, viz the alloy tube of the SW.

It becomes a real toss-up. The views through the 6" were clearly superior, but it requires so much more mount. Setting up the 5" was significantly easier. Once set-up, I did not notice any further differences in handling.


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