Results 1 to 7 of 7
Like Tree22Likes
  • 3 Post By kingclinton
  • 8 Post By jerryTheC
  • 8 Post By skaven
  • 3 Post By not_Fritz_Argelander

Thread: visual brightness...exit pupil

  1. #1
    Petre's Avatar
    Petre is offline White Dwarf
    Points: 93, Level: 1
    Level completed: 86%, Points required for next Level: 7
    Overall activity: 0%
    Achievements:
    2 Posts Achievement
    Join Date
    Apr 2017
    Location
    Romania
    Posts
    7
    Points
    93
    Level
    1
    Thanks
    1
    Thanked 0x 0 Posts

    Default visual brightness...exit pupil



    Hi! Initially, I wanted to buy a 127 Mak or a 80 ed-apo, but now I am thinking of a 10 inch truss Dob from Skywatcher or a clasic 10 inch Dob from Orion, because I want to see bright planets and other objects.. I am a little bit confused in choosing best eyepieces regarding exit pupil... visual brightness. Thanks!

  2. #2
    kingclinton's Avatar
    kingclinton is offline Super Moderator
    Points: 100,009, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Overall activity: 7.0%
    Achievements:
    2 Posts Achievement20 Posts Achievement!50 Posts Achievement!5 Threads Achievement!Blogger Achievement!
    Join Date
    Nov 2012
    Location
    Earth
    Posts
    16,175
    Points
    100,009
    Level
    100
    Thanks
    6,423
    Thanked 6,705x 4,378 Posts

    Default Re: visual brightness...exit pupil

    Try reading this article and see if that helps you at all.

    http://www.astronomyforum.net/astron...gabby+eyepiece
    DeanD, Lowjiber and ProfEclipse like this.
    .

  3. #3
    Raymondhow's Avatar
    Raymondhow is offline Gold Supporter
    Points: 34,727, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Overall activity: 10.0%
    Achievements:
    2 Posts Achievement20 Posts Achievement!50 Posts Achievement!5 Threads Achievement!200+ Posts Achievement!
    Join Date
    Mar 2014
    Location
    Oakland, California
    Posts
    4,749
    Points
    34,727
    Level
    100
    Thanks
    881
    Thanked 2,101x 1,290 Posts

    Default Re: visual brightness...exit pupil

    Quote Originally Posted by Petre View Post
    Hi! Initially, I wanted to buy a 127 Mak or a 80 ed-apo, but now I am thinking of a 10 inch truss Dob from Skywatcher or a clasic 10 inch Dob from Orion, because I want to see bright planets and other objects.. I am a little bit confused in choosing best eyepieces regarding exit pupil... visual brightness. Thanks!
    A good exit pupil for bright planets is about 1.5-2 mm. Those 10" Dobs are both f/4.7. An 8mm focal length eyepiece would give exit pupil of 8/4.7 = 1.7mm. In my 8" f/5.9 Dob, I use a 10mm eyepiece to get about the same exit pupil, 10/5.9 = 1.69mm.
    Raymond Howard
    Outreach Coordinator, Eastbay Astronomical Society
    Master Observer #204, Astronomical League

    12.5" f/6 custom Dob by New Moon Telescopes, Orion XT8 f/6 "ruby-red" Dob. Finders 13x80 Stellarvue RACI, 9x50 Orion RACI. Eyepieces 34mm Explore Scientific 68°, 24mm ES 68°, 16mm ES 68°, 10mm TeleVue Delos 72°, 7mm TeleVue DeLite 62°.

    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.

  4. #4
    jerryTheC's Avatar
    jerryTheC is offline Super Moderator
    Points: 26,972, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Overall activity: 11.0%
    Achievements:
    365 Days+ Registered Achievement!50 Posts Achievement!5 Threads Achievement!200+ Posts Achievement!First 1000 Experience Points
    Join Date
    Apr 2011
    Location
    Harrow, UK
    Posts
    6,031
    Points
    26,972
    Level
    100
    Thanks
    335
    Thanked 1,915x 1,623 Posts

    Default Re: visual brightness...exit pupil

    Bigger exit pupils mean a brighter image (but lower magnification in the same scope).
    At more than about a 2mm exit pupil, the magnification is likely to be too low to show you the finest detail your scope can resolve (but will give you a wider field of view and brighter image).
    A 1mm exit pupil will give you the highest "everyday" magnification ( = objective size in mm).
    Given very good seeing conditions (which can be rare) you can go to around a 0.5mm exit pupil (magnification = 2x objective size in mm, which is what many manufacturers quote as a maximum magnification). In most cases,
    using more magnification doesn't show any more detail - you just get a bigger, fuzzier and fainter result.

    With near perfect seeing and a premium apo refractor you can sometimes push the magnification even higher,
    but as the exit pupil gets smaller, floaters (debris in your eye) become much more obvious.
    <i><span style="font-family: Times New Roman"><font size="2"><b>SCT:</b> N11GPS <b>Refractors:</b> FS-60C/CSV, ZD-66, A80SS, FSQ106ED <b>Binoculars:</b> 8x42, 15x70<br /><b>Eyepieces:</b> 40mm Meade SWA, 28mm UWAN, 17mmT4, 12mmT4, 2.5mmT6 Nagler, 17mm, 8mm, 5mm LVW, HI-LE2.8<br /> <a href="
    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    target="_blank"><i><font size="2"><span style="font-family: times new roman">Astronomy Forum Rules &amp; Terms of Service</span></font></i></a>

  5. #5
    CloudyNight's Avatar
    CloudyNight is offline Bright Giants
    Points: 5,623, Level: 51
    Level completed: 37%, Points required for next Level: 127
    Overall activity: 0%
    Achievements:
    2 Posts Achievement20 Posts Achievement!365 Days+ Registered Achievement!750 Days+ Registered Achievement!First 1000 Experience Points
    Join Date
    Sep 2012
    Location
    Maryland
    Posts
    231
    Points
    5,623
    Level
    51
    Thanks
    55
    Thanked 69x 64 Posts

    Default Re: visual brightness...exit pupil

    Quote Originally Posted by Petre View Post
    Hi! Initially, I wanted to buy a 127 Mak or a 80 ed-apo, but now I am thinking of a 10 inch truss Dob from Skywatcher or a clasic 10 inch Dob from Orion, because I want to see bright planets and other objects.. I am a little bit confused in choosing best eyepieces regarding exit pupil... visual brightness. Thanks!
    Keep in mind that bigger reflectors have significant CO (central obstruction) from secondary mirror reducing contrast. It doesn't matter for faint DSOs because they are dim anyway, but not so good for planetary. A good quality APO refractor shows more contrast so would be better for planetary observations. But if you want observing all kind of objects a larger Dob of course is the way to go because light gathering ability is one of major limiting factors for faint DSOs.
    Zhumell Z8 8" f/6 Dob; Meade 2090 90mm Achromat.
    DSO setup for the Dob: 32mm Agena SWA, 20mm ES68, 18mm & 11mm ES82, 14mm & 8.8mm Meade 5K UWA, 12mm TV Delos, 6.5mm Meade 5K HD-60. Planetary setup: 6mm & 10mm BCO, 8mm RKE, 7mm Antares Ortho; RO Zoom 7-20mm; 1.25" 2x Meade TeleXtender, 2" 2x AT ED
    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    .

  6. #6
    skaven's Avatar
    skaven is offline HYPER GIANT
    Points: 39,671, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Overall activity: 0%
    Achievements:
    50 Posts Achievement!5 Threads Achievement!200+ Posts Achievement!First 1000 Experience Points5+ Referrals Achievement!
    Join Date
    Dec 2011
    Location
    San Diego
    Posts
    2,697
    Points
    39,671
    Level
    100
    Thanks
    180
    Thanked 1,927x 966 Posts

    Default Re: visual brightness...exit pupil

    Quote Originally Posted by CloudyNight View Post
    Keep in mind that bigger reflectors have significant CO (central obstruction) from secondary mirror reducing contrast. It doesn't matter for faint DSOs because they are dim anyway, but not so good for planetary. A good quality APO refractor shows more contrast so would be better for planetary observations. But if you want observing all kind of objects a larger Dob of course is the way to go because light gathering ability is one of major limiting factors for faint DSOs.
    Not necessarily. There is a reason that the top amateur planetary photographers use 14" SCTs -- more aperture == higher resolution. The comparatively huge central obstruction in an SCT does reduce contrast, but the additional aperture outweighs it. The legendary Thierry Legault even has a page about this on his website: Thierry Legault - What are the effects of obstruction ? He concludes at the end that a reasonable rule of thumb is that you can take the aperture diameter of an SCT or reflector, subtract the diameter of the obstruction, and the resulting measure is more-or-less the "equivalent" APO refractor diameter, in terms of contrast. So a 10" reflector with a 30% central obstruction will perform like a 7" APO refractor -- way better than a 4" APO at likely 2-5x the cost.

    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.

    C10-N/C14+Losmandy G11; Portaball 12.5"; NexStar 6SE; Meade ETX125; Stellarvue F80
    Meade HD-60 9mm, 6.5mm; 56mm; University Optics Orthoscopic 12.5mm, 9mm, 7mm, 5mm;
    ES 70° 15mm, 20mm; ES 82° 30mm, 18mm; ES 100° 9mm; Baader Hyperion 24mm; TV Nagler T6 13mm
    William Optics Binoviewer; GSO 2" 2x ED barlow; 5x APO barlow, Parks 2.5x APO barlow
    Filters: Orion Ultrablock, Thousand Oaks OIII

  7. The Following 2 Users Say Thank You to skaven For This Useful Post:

    j.gardavsky (05-21-2017),michael131313 (05-21-2017)

  8. #7
    not_Fritz_Argelander's Avatar
    not_Fritz_Argelander is online now HYPER GIANT
    Points: 183,498, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Overall activity: 78.0%
    Achievements:
    365 Days+ Registered Achievement!2 Posts Achievement20 Posts Achievement!750 Days+ Registered Achievement!First 1000 Experience Points
    Awards:
    Thread Award
    Join Date
    Jul 2011
    Location
    US
    Posts
    22,042
    Points
    183,498
    Level
    100
    Thanks
    7,254
    Thanked 46,398x 14,955 Posts
    Blog Entries
    59

    Default Re: visual brightness...exit pupil

    For DSOs dialing in the right exit pupil can make the difference for detection.
    j.gardavsky, jerryTheC and Gabby76 like this.

    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    : Refractors:

    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    ST80 (mods for white light solar), SV ED80 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 Binocular Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker III, Vixen Porta II, Celestron CG5, Orion
    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    EQG

 

 

Similar Threads

  1. Exit Pupil
    By staffop in forum Astronomy Beginners Forum
    Replies: 2
    Last Post: 07-04-2015, 10:16 PM
  2. Exit Pupil, AFOV, and brightness
    By Albireo in forum Astronomy Beginners Forum
    Replies: 3
    Last Post: 08-14-2012, 12:34 AM
  3. when eye pupil smaller than exit pupil.. and CO question
    By Paulie in forum Amateur Astronomy Forum
    Replies: 4
    Last Post: 01-18-2009, 06:51 AM
  4. exit pupil brightness reduction
    By Tenifer in forum Amateur Astronomy Forum
    Replies: 2
    Last Post: 11-16-2007, 02:42 PM
  5. exit pupil
    By Tom Rauschenbach in forum Amateur Astronomy Forum
    Replies: 2
    Last Post: 05-23-2006, 05:43 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Powered by vBulletin® Version 4.2.0
Powered by vBulletin®
All times are GMT. The time now is 05:50 PM.