I understand the effect but what makes a scope have a large or small eye box and critical or non critical eye relief?

What is the trade off as I assume there is one?

What scopes other than Leupold in the $400-$800 range have large eye boxes?

I can't answer most of your questions at all. But I do suspect that scopes with small eye boxes do have a touch better resolution. E

Just generally speaking, the size of the eye box is controlled by the design of the ocular assembly. You have probably noticed as of late that alot of the newer scope designs (Minox, Meopta Meopro, Leica..) have rather larger ocular housings. From what I understand, if the manufacturer wants good eye relief, eye box and FOV, it can be accomplished easier with a larger ocular assembly (larger internal lenses that is) where as in the past you had to suffer a lessor FOV with a longer eye relief design.

So the trade off with these type designs is that they can present an obstacle with bolt action rifles in that often there is very little clearance between the bolt handle (lift) and the ocular assembly when operating the bolt action itself.

Scopes in that price range I'm familar with would be the Elite 6500 series variables with their 4"-5" inches of eye relief depending on the model.

I was under the impression that larger oculars were to allow for a brighter image.
The biggest eyeboxes I've ever seen were on Scout Scopes with 9-14 inch eye relief. After that, the fixed magnification Leupolds like their FXII, 4X. None of these designs have large oculars. E