Scope eye box

[Alex Wheeler]

What determines the eye box of a scope? Exit pupil? By eye box I mean how critical your eye position is behind the scope.

I am also wondering what scopes you guys are using for free recoil shooting? Eye box becomes critical to fast shooting, I am finding difficulty finding the scope again after the shot as quickly as I'd like. I am switching to extra tall rings to get my cheek away from the gun, which should make finding the scope even harder.
Alex

 

[Alex Wheeler]

Thanks Tom, I have a br on my F class rig, both can't make weight with it on my light gun. I have read the NXS has a big eye box, and extra eye relief. But then your back to the weight issue again. I just have a very heavy stock.

 

[medic727]

Eye box/exit pupil is calculated by dividing the objective diameter by the power setting. So, a at higher magnification the eye box/exit pupil gets smaller. Hence, eye position becomes more critical. This is true of all scopes, it is a fundemental principle of optics.

 

[dickn52]

Exit pupil is the number used to show light transmission thru the optics. Higher the number, brighter the picture. Medic727 has the right math for finding the exit pupil.

 

[medic727]

One thing I forgot to mention in my previous reply was how exit pupil size works when you have cataracts. I use a Leupold Zero Point boresighter for my initial zero after a scope swap. I know there are multiple ways to zero your scope. But, the Zero Point provides another major benefit. The way the boresighter works optically led me to find out I had cataracts. When looking through my scope at the boresighter image I saw this "wrinkly" blob in the image. Hmmmm, gotta clean my scope. Nope, that didn't work. Clean the lens on the boresiter. Nope, that didn't work either. So, I figured it must be a defect in the boresiter and continued on. Several months later I had an appointment with my ophthalmologist. She told me I had the beginnings of cataracts, smack in middle of the lenses. Then I explained what I found when using the boresiter. She told me that would be a great way to self-monitor the progress of the cataracts. So, as time went on I noticed that targets, especially at long range, were getting foggy, so I went back to the ophthalmologist. She explained that at lower mag (larger exit pupil) most of the image passing around the cataract. As mag increased (decreasing exit pupil) more of the image was passing through the cataract. Hence, the fogginess. Post-cataract surgery all of the image was now clear. No blobs, no foggy image.

So, this was the long way around of explaining how exit pupil can interact with cataracts.