Rifle Scopes Exit Pupil Reality

[priler]

hello all,new member here with a few questions.

is there any way to know the real exit pupil of any scope(particularly interested in low magnification range at the moment/need/application) beyond the simple table experiment(impractical unless in hand) of actually measuring it yourself?

i'm asking this because it seems to me that there are several manufacturers out there that are actually lying about the true exit pupil(for some models) and are simply using the formula of objective lens diameter divided by magnification setting,which doesn't seem to hold true. some vendors are doing the same thing even when the manufacturer doesn't even give the exit pupil.

in this context,it seems that exit pupil is just a made-up term but the fact is,with a little patience,i can still measure it myself and get the true measure.

example,leatherwood CMR 1-4x24=11.1mm @ 1x this seems true.

burris MTAC 1-4x24=24mm @ 1x this seems false.

i can give many more examples that seem(and sometimes are because i have the model) true and others that seem false or totally unrealistic.

so,without buying every single scope that i'm comparing,how do i go about truely knowing,..or is there just no way unless you have it right in front of you? (i'm guessing no)

some makers don't even want to give this number,probably because of the issue i'm addressing here and probably so it doesn't hurt sales.

what say you?

 

[glock24]

Re: Exit Pupil Reality

http://www.snipershide.com/forum/ubbthre...452#Post2997452

 

[TiroFijo]

Re: Exit Pupil Reality

At high magnification generally the exit pupil is: objective diameter / magnification

At the lower end this is rarely true, because there are many other design constrains that limit exit pupil.

Many manufacturers just "round up" numbers, for example the NXS 3.5-15 is really a 3.5-14, easy to realize when you see their exit pupil specs.

I don't know how to measure it.

In low magnification scopes, keep in mind that at 1X you should take the objective diameter and substract at least the erector thickness and space for adjustmente. For example a 1-4x24 scope has a 24 mm objective, but light has to pass through the erector and finally you would get something along 16 mm or less.

 

[Plange]

Re: Exit Pupil Reality

One way to get a true measurement is to use a strong light source more than 25 feet away and aim the scope at it. Take a piece of frosted glass and move that back and forth at the ocular end until you get a perfectly focused circle- the size of that circle is your exit pupil.
I have a fixture here that I use to measure this and a graduated frosted lens with measurements on it.
Just be sure the light source is far enough away or else you will poor readings.
Thanks,
Paul

 

[CoryT]

Re: Exit Pupil Reality

I'm not sure what the actual issue is, since the eye is at maximum about 7mm, so an exit pupil larger than that has basically no effect on anything anyway.

While it may provide an apparent increase in the size of the 'eye box', not being centered will lead to parallax errors. So, the mere fact you don't see a shadow effect with more head movement still provides no realistic advantage to a 24mm exit compared to say a 15mm exit.

 

[priler]

Re: Exit Pupil Reality

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: glock24</div><div class="ubbcode-body"> http://www.snipershide.com/forum/ubbthre...452#Post2997452 </div></div>

thanks. David S gives good answer on #1.

 

[priler]

Re: Exit Pupil Reality

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TiroFijo</div><div class="ubbcode-body">At high magnification generally the exit pupil is: objective diameter / magnification

At the lower end this is rarely true, because there are many other design constrains that limit exit pupil.

Many manufacturers just "round up" numbers, for example the NXS 3.5-15 is really a 3.5-14, easy to realize when you see their exit pupil specs.

I don't know how to measure it.

In low magnification scopes, keep in mind that at 1X you should take the objective diameter and substract at least the erector thickness and space for adjustmente. For example a 1-4x24 scope has a 24 mm objective, but light has to pass through the erector and finally you would get something along 16 mm or less. </div></div>

best answer thanks,makes perfect sense. it is after all a tube inside a tube not to mention the true magnification on the lowest setting. i wonder if there's a correlation between the elevation/windage adjustment available and exit pupil(and maybe erector diameter).

 

[priler]

Re: Exit Pupil Reality

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CoryT</div><div class="ubbcode-body">I'm not sure what the actual issue is, since the eye is at maximum about 7mm, so an exit pupil larger than that has basically no effect on anything anyway.

While it may provide an apparent increase in the size of the 'eye box', not being centered will lead to parallax errors. So, the mere fact you don't see a shadow effect with more head movement still provides no realistic advantage to a 24mm exit compared to say a 15mm exit.

</div></div>

your thinking like a hunter comfortable and patient in a stand or at a range,..try thinking like a LEO doing entry-work or a big game hunter and up close. still,your point is well taken. thanks,appreciate.

 

[BigJimFish]

Re: Exit Pupil Reality

I have done what I can to explain this on my low power multipurpose scope review thread.

http://www.ar15.com/forums/t_3_18/421244...html&page=1

Idealized values have been removed from the table and I have added values for a few scopes that I measured myself. The measuring apparatus can be seen in the Vortex Razor review on page 17. Keep in mind that my measuring apparatus is not great and therefore some error exists in the values I was able to obtain. This is obvious in that some of them are not even technically possible (ie. 6.7mm at 4x for a 1-4x24mm scope.) Nevertheless, these measured values are certainly more useful than idealized values, especially at 1x.

Also, as was mentioned by David, exit pupil is one of the two factors effecting eye box and eye box is vital in a scope being used for close quarters. Unfortunalty, no standardized reporting data seems to exist for eye relief range at 1x. Eye relief is typically reported at each end of the magnification range of a scope as a single number and not a range. It is, therefore, hard for a shooter to have a good idea about the eye box of a scope from its specifications.

 

[TiroFijo]

Re: Exit Pupil Reality

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CoryT</div><div class="ubbcode-body">I'm not sure what the actual issue is, since the eye is at maximum about 7mm, so an exit pupil larger than that has basically no effect on anything anyway.

While it may provide an apparent increase in the size of the 'eye box', not being centered will lead to parallax errors. So, the mere fact you don't see a shadow effect with more head movement still provides no realistic advantage to a 24mm exit compared to say a 15mm exit.

</div></div>

It does matter when talking about 1X scopes, the larger the exit pupil the more forgiving the eye position for quick shots. You are basically trying to mimic red dot scopes, but you still heve eye relief issues and less forgiving eye position.

 

[priler]

Re: Exit Pupil Reality



excellent BigJimFish,great work. lots of good info there.