Originally Posted by Nvhunter
For a field report: I did side by side comparison between a Leupold VX-II 50mm and my VX-III 40mm after sunset. Astounding, my VX-III 40mm was more clear, brighter and showed better color than the 50mm....I did not have my light meter with me, but It seemed 30% better on all counts to me - and my friends.
I think glass quality is paramount. No book I ever read said that a 40mm could out perform a 50mm.
No one said the quality of the glass wasn't important. Or that Swaro glass isn't better than Tasco. Once the price and glass quality of scope has been selected, a 50mm will have some benefits over a 40mm, without a huge increase in price.
You're right, if a 50mm won't let you rest your cheek on your stock but a 40mm will, due to the lower mount on the receiver, a person ought to go with the 40mm. A 50mm will require the scope to be mounted a minimum 0.2" higher for the objective bell to clear the barrel. I've not had problems with 50mm objectives so far. Doesn't mean it isn't a valid consideration though.
I agree the quality of the glass and the glass coatings is one of the most important decisions in a scope purchase. Right up there with the mechanical reliability of the scope and turrets, and hardiness of the scope to withstand recoil without busting a gut.
But once the scope manufacturer and grade of scope has been selected, I'd recommend 50 over 40. The quality of the glass should be identical and the exit pupil will be 20% larger on the 50mm than on the 40mm. And 50mm are generally funtional for the average shooter with respect to planting the cheek on the stock. That's what I thought the question was (40 vs 50mm objectives - all other components being equal) and that's what my response addressed.
There is no one-size-fits-all answer. It would be best to be able to compare the scopes on one's rifle, but that can get pretty expensive. Thus this Forum and a collection of opinions to help with the 'better' selection on the first purchase.