Jump to content


Photo

Exit pupil accuracy....

  • Please log in to reply
6 replies to this topic

#1 ngc 9999

ngc 9999

    Mariner 2

  • -----
  • Posts: 206
  • Joined: 13 Aug 2012
  • Loc: Sunrise, Fl. 26 degrees N

Posted 06 February 2013 - 09:03 PM

Is there an binocular with an exit pupil with a roundness as perfect as a circle, or shouldn't I worry about that? :ooo:

#2 Rich V.

Rich V.

    Skylab

  • *****
  • Posts: 4016
  • Joined: 02 Jan 2005
  • Loc: Lake Tahoe area, Nevada, USA

Posted 06 February 2013 - 09:50 PM

I would expect round exit pupils on almost all newer binoculars that use BaK-4 glass for their prisms. It is best for binos with short focal ratios, which are used by most hand held designs.

Older models and some lower end binos may use BK-7 glass instead and they will show darker chords around the exit pupil that make it look diamond shaped. Many older 7x35s from the '50s and '60s use BK-7 glass.

Longer focal ratio optics like giant astro binoculars and spotting scopes can do just fine with BK-7 prisms.

Rich

#3 ngc 9999

ngc 9999

    Mariner 2

  • -----
  • Posts: 206
  • Joined: 13 Aug 2012
  • Loc: Sunrise, Fl. 26 degrees N

Posted 06 February 2013 - 10:06 PM

What I also mean is if that the exit pupil has such perfect roundness as not to virtually have measurable excentricity.

#4 GlennLeDrew

GlennLeDrew

    Voyager 1

  • *****
  • Posts: 10501
  • Joined: 17 Jun 2008
  • Loc: Ottawa, Ontario, Canada

Posted 06 February 2013 - 11:36 PM

Not quite perfectly round exit pupils are fairly likely when the objective f/ratio is very the threshold of full accommodation by the prisms. This happens when a slight lateral offset of a prism aperture clips one side of the aperture.

And the shape of the exit pupil varies over the range of angles it can be seen from behind the eyepiece.

In practice, slight non-circularity of the exit pupil is of no real consequence as long as other aspects of performance are not suffering.

#5 ronharper

ronharper

    Vanguard

  • *****
  • Posts: 2205
  • Joined: 14 Feb 2006

Posted 07 February 2013 - 12:16 AM

The Allbinos binocular review website has reviews for many binoculars. One thing they do in all their reviews is to photograph the exit pupils, and rate them against perfect roundness. Look there and you will find some perfect ones, mainly in high end binoculars, and many eccentric and clipped off ones.
Ron

#6 ngc 9999

ngc 9999

    Mariner 2

  • -----
  • Posts: 206
  • Joined: 13 Aug 2012
  • Loc: Sunrise, Fl. 26 degrees N

Posted 07 February 2013 - 09:37 AM

The Allbinos binocular review doesn't review the BA8 series parameters such as exit pupil and FOV as they do with the high end.

#7 ngc 9999

ngc 9999

    Mariner 2

  • -----
  • Posts: 206
  • Joined: 13 Aug 2012
  • Loc: Sunrise, Fl. 26 degrees N

Posted 07 February 2013 - 09:48 AM

I found the BA8 reviews as the William optics, which is the same as my Garrett Signature Series, as far as their measures, I am surprised by the binocular attribute.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics