40 v 50 v 56 mm Objective Lens

[Chrismadrid]

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.

 

[700]

Big_Bore / Buffalobob

Two factors affect twilight resolution.

1) Light gathering (brightness) capabilities of the scope which is realated to Obj. lens diameter and exit pupil.
This is calculated as

Relative Geometric Brightness = square(exit pupil))

If your eye pupil is less than the exit pupil then you substitute eye pupil in the above formula. This is because the eye pupil will have a stopping down effect on the light coming from the scope in the exit pupil. I.e. you cannot get a 8mm light beam into an eye with a 7mm eye pupil.

2) Added resolution due to increased magnification. If you can see it twice as big, then you can see it twice as clearly. This is calculated as:

Twilight Factor= square root of (mag x objective diameter )

//////////////////////////

The product of Twilight Factor and Relative Geometric Brightness might give you a better all round deal.

For a 7mm eye pupil I get the following values:-

8x56mm scope Twilight Factor*RGB = 1037
7x50mm scope Twilight Factor*RGB = 916
6x42mm scope Twilight Factor*RGB = 778
5.7x40mm scope Twilight Factor*RGB = 740

Going on these calculations, the 8x56mm has 40%% more capability than the 5.7x40mm.

This is all completely accademic for the following reasons:-

1) Even people who have the same eye pupils, their eyes may differ internally in other ways. Some might benifit more from brightness than mag., and for others the reverse might be true.

2)I assumed the scopes are of similar design and optical quality. I.e different models of the same brand.

3)The user does not wear corrective glasses/contacts. They eye pupil may have to be measured taking into account the effect of the glasses/contacts. Talk to your Doc about that. Let me know what he says.

The easies way to find which scope suits you better is put up a target just before dusk and then compare scopes as it gets darker.

Kindest regards

700

 

[ricka0]

Chris in Madrid. Ping me offline. And everyone should have an email alias in there profile /ubbthreads/images/graemlins/frown.gif
I go to Madrid once a year, but never to shoot.

 

[Chrismadrid]

[ QUOTE ]
...everyone should have an email alias in there profile /ubbthreads/images/graemlins/frown.gif

[/ QUOTE ]Yup - was just LAZY /ubbthreads/images/graemlins/blush.gif - Now added.
[ QUOTE ]

I go to Madrid once a year, but never to shoot.

[/ QUOTE ]So is it a TAPAS munching visit then? - What time of year generally?