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40 v 50 v 56 mm Objective Lens

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Old 07-21-2005, 11:56 PM
Silver Member
Join Date: Nov 2004
Location: GF Montana
Posts: 467
40 v 50 v 56 mm Objective Lens

I went to the eye doc today and had him measure my max pupil - it came out 7mm. (probably was 8mm 20 years ago [img]/ubbthreads/images/graemlins/frown.gif[/img] )

Using the simple Formula Obj/Power = exit diameter (ED) I calculated the max power I could put my favorite scopes under low light conditions and not suffer blackout.

Plugging in my 7mm: Obj/ED = Power <ul type="square">[*]56/7 = 8 Power[*]50/7 = 7 Power[*]40/7 = 5.7 Power[/list]Now you can't judge a scope simply by Objective Lens, but you can probably compare a Loopie VX-III 40 v. 50, or a NF 50 v. 56
A fun thing to do is put point your scope near a light (arms length away), and turn the power up and down and see the exit pupil dilate/contract.
Is it worth the extra money going from 40 to 50 mm on a loopie or 50 to 56 on a NF? In the case of NF I doubt it as most scopes the question is 40 v 50.
The total light gathered is limited by the Obj lens is simply pi*(Obj/2)^2 - so light input goes up as the square of Obj lens - <font color="purple">BUT </font> additional height is simply Obj/2 - so going from 50 to 56mm only requires 3mm more height.
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Old 07-22-2005, 07:26 AM
Platinum Member
Join Date: Jun 2001
Location: Potomac River
Posts: 5,057
Re: 40 v 50 v 56 mm Objective Lens

Big Bore

I never did make very good grades in optics nor E &amp; M. I still have my optics book but hate to go and open it (bad memories).

As we previuosly discussed, I have an old scope that I can no longer see through. I had thought that it was just the scope was old and maybe the coatings had gone bad. It is really irritating to find out that it is me that has gotten old.

Anyway, I like your bottom line calculation although I do not agree with your conclusion about the 56. If I remember correctly someone is making a 72mm obj which gets you up to 10.3X. My conclusion is that if your eyes are going downhill then spend money on optics to compensate plus anyone who has ever tried to put horns on a deer or elk late in the day knows that it is not the determination that the animal is a deer or elk, it is the resolution of the antlers. You cannot put the crosshairs on it and a finger on the trigger unless you can resolve antlers. It has been a long time since I have hunted elk but it is my understanding that nowdays some states regulate by number of point on the antlers ( cow ,spike, mature bull ). This makes things very critical at long range. Maybe if you are buying a scope for a gun that is intended for whacking rocks, pdogs or chucks this is not very important.
The Smokin Fur Rifle Club
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Old 07-22-2005, 12:12 PM
Platinum Member
Join Date: Dec 2001
Location: Long Island, New York
Posts: 2,104
Re: 40 v 50 v 56 mm Objective Lens

Here is my take on this issue:

I'll start by stating that in my experience, optical resolution far outweighs magnification in a hunting scope, everytime. I'll take a high quality/lower magnification optic over a mid quality/higher magnification scope when afield. Having a target animal appear larger but without great clarity is not nearly as important as having a crisp image with great clarity even if the target animal is smaller in appearance.

As to light gathering abilty: As you have pointed out; with a smaller objective lens all you have to do is reduce the magnification a bit to allow the same exit pupil (diameter of light coloumn) as the larger objective lens allows. In low light conditions it would be unlikely that there would be much benefit of having a slight increase in magnification anyway. At dusk and dawn simply adjust the magnification to allow the maximum exit pupil for your use. Yes - a larger objective lens would allow you to set the magnification slightly higher if that was important. I might add that according to my opthmologist(sp), most adults will only dilate to a maximum of about 6mm, and that is in near total darkness.

There is , however, one benefit of a large exit pupil (7mm - 8mm - 9mm) that you don't normally see considered. If your eye can only use 6mm of light (your max dilation), a larger column of light at the ocular lens will allow you to align your eye with the center of the scope easier and faster.

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Old 07-22-2005, 07:08 PM
Posts: n/a
Re: 40 v 50 v 56 mm Objective Lens

Hensholdt manufactures a 70mm Objective that is pretty awesome. Mounting is not a problem; however the height above bore might be ~ for you. Price? Above $3,000.00.

Does it gather light? No, but it transmits it exceptionally well.
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Old 07-22-2005, 11:32 PM
Platinum Member
Join Date: Dec 2001
Location: Long Island, New York
Posts: 2,104
Re: 40 v 50 v 56 mm Objective Lens

Sounds like the perfect scope for a pair of quick disconnect rings. If the goin' gets tough it would make a great club. [img]/ubbthreads/images/graemlins/grin.gif[/img]

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Old 07-23-2005, 12:51 AM
Silver Member
Join Date: May 2005
Location: Madrid - Spain
Posts: 315
Re: 40 v 50 v 56 mm Objective Lens

Big Bore - As a matter of interest - did you have your MIN EP measured?. Is it around 2mm - It's something that intrigues me - sorry for the mini-hijack.

I concur also with VH comment on LARGE EP's. I've a russian 4*48 that is frankly incredible to use at night - it's never a problem to line up with. It's lousy in daylight though!
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Old 07-23-2005, 08:09 AM
Bronze Member
Join Date: Aug 2001
Location: Chicago, IL
Posts: 82
Re: 40 v 50 v 56 mm Objective Lens

I've always stuck with 40mm objective lenses because the 50mm or 56mm require much higher mounts, which takes my cheek off the stock. Of course if you have an adjustable cheekpiece stock, that problem goes away.
Jesus saves, but Moses invests
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