Exit Pupil Vs. Aperture

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Refractordude
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Exit Pupil Vs. Aperture

#1

Post by Refractordude » Thu Jan 02, 2020 4:13 am

Is this true? Click image and read the underlined. Thanks to you all.
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Telescopes: Meade LX70 120mm f/8 Refractor, Vixen 70mm f/12.9 Refractor, Tasco 49N 50mm Red Refractor
Binoculars: Zhumell 20x80 Giant, Levenhuk Sherman 7x50
Mounts: Orion SkyView Pro Equatorial, Orion Versago II Altazimuth, Farpoint Universal Parrallogram Mount
Finders: GSO 8x50 Raci, Svbony Red Dot
Diagonals: GSO Dielectric 2", GSO Dielectric 1.25"
Eyepieces: GSO Plossls 32mm/25mm/20mm, GSO 20mm Superview, Svbony 20mm/15mm/9mm/6mm, Svbony Aspheric 23mm/10mm/4mm, Agena Super Wide Angle 15mm, Few No Name Brand Ebay Plossls
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#2

Post by AntennaGuy » Thu Jan 02, 2020 5:09 am

Yes, I believe that is correct. But... the 25x100 binoculars will provide more magnification. And if you want 25x magnification, it is certainly better to have a 100mm objective than a 70mm objective! Caveat: I'm not an expert. Others on this forum with far more knowledge and experience may wish to chime in. Best regards.
* Celestron C6 SCT on a Twilight 1 Alt-Az mount
* Meade 323 refractor on a manual equatorial mount.
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#3

Post by Bigzmey » Thu Jan 02, 2020 5:25 am

Yes, assuming your eye pupil can dilate to 7mm. Also, I find views with exit pupil above 5mm too washed out and lacking contrast and prefer 4mm exit pupil.
Scopes: Stellarvue: SV102 ED F7; Celestron: 9.25" EdgeHD F10, 8" SCT F10, 6" SCT F10, Omni XLT 150R Achro F5, Onyx 80ED F6.3; Meade: 80ST Achro F5.
Mounts: ES: Twilight I; Bresser: EXOS2; SW: SkyTee2, AzGTi; UA: MicroStar.
Binos: Orion: Little Giant II 15x70, WorldView 10x50, Nikon: Action EX 8x40.
EPs: Pentax: XWs; TeleVue: Delites, Panoptic, Plossls & barlows; ES: 68s; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV; Meade: UWAs & Plossls.
Diagonals: Baader: BBHS silver mirror, Zeiss Spec T2 prism, Clicklock dielectric; TeleVue: Evebrite dielectric.
Filters: Lumicon: DeepSky, UHC, OIII, H-beta; Baader: Moon & SkyGlow, Contrast Booster, UHC-S; Astronomik: UHC, Orion: UltraBlock, SkyGlow.
Observing: DSOs: 1694 (Completed: M110, H1, H2. In progress: H3: 195, H2,500: 1272, S110: 77). Doubles: 1150, Comets: 14, Asteroids: 73
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#4

Post by notFritzArgelander » Thu Jan 02, 2020 5:38 am

Yeah but "brighter" is not the same as "more contrast". Smaller exit pupils will provide more contrast since the sky background gets darkened.
Scopes: Refractors: Orion ST80, SV ED80 A f7; Newtonians: Z12 f5; Catadioptrics: VMC110L, Intes MK66. EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker III, Vixen Porta II, Celestron CG5, Orion Sirius EQG
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#5

Post by DeanD » Thu Jan 02, 2020 5:42 am

Yeah, what they said. ;)

It depends what you want the binos for: 7x50 with 7mm exit pupil will give you a bright image for sure, but a lot of objects will be next to invisible because the background sky will be too bright and the objects are too small. Contrast, surface brightness and object size will determine how well you see a lot of DSO's: so higher power with the same objective diameter will often enable you to easier see (say) galaxies or planetary nebula which are effectively invisible in the brighter, but lower power view.

Most of us don't have 7mm pupils any more either: so some light is wasted and you might find that 7mm exit pupils give you no "brighter" view than 5mm, especially in suburban skies when your eyes can't fully dark adapt.

A lot of expert bino observers will tell you that an easy way to determine a binocular's over-all suitability for astro viewing is to multiply the magnification by the objective lens diameter. Usually, the higher the number the better. 7x50's give you 350, while 11x70's give 770, 25x100's give 2500, etc. (Mind you, the naked eye view gives a number of 1x7=7 (maximum): so any binocular will give you amazing views compared to nothing at all!!!)

As for telescopes and eyepieces there are lots of factors involved, and no one instrument is suitable for everything...

Many people enjoy the portability of binoculars and hand-holding, but of course the higher the power and the larger the binocular the harder this becomes.

There are lots of articles, books, and discussions out there about all this, so that is enough from me for now! ;)

All the best,

Dean
Telescopes: 12" f5 dob, Celestron CPC800, 150mmf5 Celestron achro, Tak TSA102, TV76, ETX125...
Binos: Tak 22x60, Swarovski 8x30 Habicht, FB 25x100, Orion Regulux 15x70...
Eyepieces: way too many (is that possible?), but I do like my TV 32mm plossl, 13mm Nagler T6, 27mm Panoptic and 3-6mm Nagler zoom, plus Fujiyama 18mm and 25mm orthos and Tak 7.5mm LE
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#6

Post by russmax » Fri Jan 17, 2020 8:04 pm

Is the brightness proportional to the objective's diameter or area? That would change my answer about the correctness of the underlined text.
--Russmax
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Celestron AVX 8" SCT & Omni XLT 102 AZ
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