40 v 50 v 56 mm Objective Lens

Discussion in 'Long Range Scopes and Other Optics' started by ricka0, Jul 21, 2005.

1. ricka0Well-Known Member

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

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.

2. BuffalobobWriters Guild

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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.

3. Varmint HunterWell-Known Member

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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.

VH

4. GuestGuest

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.

5. Varmint HunterWell-Known Member

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

VH

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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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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.

8. ricka0Well-Known Member

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[ QUOTE ]
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.

[/ QUOTE ]
<font color="purple"> buffalobob </font> - exactly. My comparision was just between lenses of identical quality. Cheap + Big will not resolve betwen that big spike elk and a two point. (Montana now looks at horns).
[ QUOTE ]
<font color="brown"> 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. </font>

[/ QUOTE ]
Excellent Point!
I've alway been a big beliver of getting the best optics you can afford (then going up one nothch /ubbthreads/images/graemlins/smile.gif)
Varmint Hunter writes:
[ QUOTE ]
<font color="brown"> I'll start by stating that in my experience, optical resolution far outweighs magnification in a hunting scope, </font>

[/ QUOTE ] No question.

9. ricka0Well-Known Member

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[ QUOTE ]
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.

[/ QUOTE ]
No, wish I had thought of it. I've read it's aournd 2mm. Ther was no mention of it getting worse with age (as dialation does). Not a hijack at all. Good questions.
<font color="purple"> [ QUOTE ]
I've a russian 4*48 that is frankly incredible to use at night

[/ QUOTE ] </font> Cool. A night scope.

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[ QUOTE ]
[ QUOTE ]
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.

[/ QUOTE ]
No, wish I had thought of it. I've read it's aournd 2mm. Ther was no mention of it getting worse with age (as dialation does). Not a hijack at all. Good questions.

[/ QUOTE ]

I did my own "testing" about three years ago using a whole stack of scopes - Mine is a "tadge" over 2mm. Mine has increased slightly over the last three years!

It's frankly quite shocking as SUDDENLY the image goes muck "darker" and you'll start to see things floating about - its the flotsam that we all have floating about on the surface of our eyes.

Interesting though is that at less than 2mm the depth of field increases due to the "pinhole camera" effect

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[ QUOTE ]
I've a russian 4*48 that is frankly incredible to use at night

[/ QUOTE ] </font> Cool. A night scope.

[/ QUOTE ]It'll be even better once it gets a GEN2+NV adapter fitted /ubbthreads/images/graemlins/wink.gif

12. 700Well-Known Member

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Bore

I tought 7mm exit pupil was just applicible to young grunts. You lucky man. I must get mine measured at my next
(overdue) eye test.

I have have an Excel spread sheet done on exit pupil/objective lens diameter/ magnification.

I am happy to email it to you and talk you through it(by email, because I'm in Ireland).

Remove the XXX's from the email address.

Kindest regards

700

13. BuffalobobWriters Guild

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Chris or 700

So with your testing and calculating what did you conclude. Are the larger objective lens better or worse or doesn't matter for those of us who are been down more than a few bumpy roads and don't have all of our original equipment functioning well?

14. ricka0Well-Known Member

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[ QUOTE ]
Bore
I tought 7mm exit pupil was just applicible to young grunts. You lucky man. I must get mine measured at my next
(overdue) eye test.

[/ QUOTE ]

The doc said youngsters come in at 8 and higher.