Re: 40 v 50 v 56 mm Objective Lens
Well I started to look at things differently (pun not intended).
I start now with the premise that my right eye really only gives me an EP of about 2,5mm to about 6mm. Then decide what magnification I need and pick an objective that fits the bill. If its for poor light I err bigger - Spanish summer daytime use and I err smaller.
So for precision stuff I tend to use 20mag (or more if possible) hence I'm waiting for a 5-25*56mm S&B from Pete - but for daytime general purpose I'm happy with a 10*42 and a 4-16*50 Horus (generally between 12 and 16) - For poor light, an 8*56 and the 4*48. I'mm umming about a 6*42 at the moment as 8mag is often a bit much and the 4 a bit low for my liking.
ime it does make a difference if you need magnification. EP's lower than 2,5mm are horrible (imo)- I've been as low as 0,9mm and I cant get on with it. If you can keep the EP between 3mm and 5mm on a smaller lens - do it.
Hope that's helped a bit.