bruce_ventura
Well-Known Member
Correction Re: Question about exit pupil for scopes with really high magnification.
This morning I realized that I made math errors in my post. That sucks, because now I have to correct my own post. I was away from my computer yesterday and tried to post from my iphone, which is also my calculator. Bad idea. Much better to use a keyboard and screen to edit. Sorry about that guys, but as Longshooter said, this is the net. Here's the correct math:
For a 50 mm scope, reduce all the magnification values above by 11%. So, for an adult with good vision, the optimum magnification for a 50 mm scope is about 22X.
When I look at these magnification values, I'm a bit astonished that the limits are so low. If 22X is the upper limit for a 50 mm scope due to physics, then why are there so many 50 mm scopes with 24X+ magnification out there from reputable companies like Leupold, Zeiss and Swarovski?
One reason is that there are a lot of shooters with poor vision. I'm reminded of this all the time at the range. Astigmatism is the most common problem. Remember that the diopter ring corrects for focus, but not astigmatism. If more shooters knew this, they would get their eyes checked and wear correction when shooting. Wearing glasses is a much better solution than buying a higher magnification scope.
Another reason is that we are all lazy. Why force ourselves to concentrate on features that are at the limit of our visual acuity, when we can simply boost the magnification and make those (blurred) features larger? However, the scope magnification is optimum when the eye can just begin to perceive the blur. The eye doesn't actually see more detail at higher magnification, and we pay for the higher magnification in terms of lower brightness and lower image contrast (due to higher glare).
Some compromise is OK. Up to about 3X loss of brightness in daytime is not a bad thing because your eye can quickly accommodate this change in brightness. Loss of image contrast is usually bad for hunting (because target features have low contrast to begin with), but it's more tolerable for target shooting (because man-made targets are usually high contrast). So, for strictly target shooting applications, one could argue that up to about 40X magnification for a 50 mm scope has some value because target details are a little "easier" to see (i.e., they require less concentration).
Personally, I set the upper limit at 25X for a 50 mm scope. Granted I have good vision and target shoot mainly to train for hunting. When I look at my stable of scopes, there isn't one 50 mm scope that goes above 25X. All my variable magnification scopes go down to at least 6X, which provides a wide enough field of view for rapid target acquisition.
Finally, I haven't included the effect of turbulence-induced blur on image quality. Turbulence, not the scope, is usually the limiting factor on image resolution in daytime, especially when looking over flat terrain on a sunny day. This is another reason why high magnification scopes have dubious value.
This morning I realized that I made math errors in my post. That sucks, because now I have to correct my own post. I was away from my computer yesterday and tried to post from my iphone, which is also my calculator. Bad idea. Much better to use a keyboard and screen to edit. Sorry about that guys, but as Longshooter said, this is the net. Here's the correct math:
"2. The resolution of a really good telescope is loosely called the "diffraction limit". For a 56 mm objective telescope the resolution is about 25 times better than the adult eye, or about 17 times better than a young, exceptional eye.
So, above a magnification of roughly 21X, give or take, a 56 mm objective telescope is magnifying blur - it's not providing any more detail about the target to someone with good vision. Below that magnification, the eye is the limiting factor.
[Yes, the eye with better acuity sees the telescope-induced blur at a lower magnification, not a higher one]
If you have vision problems that cannot be improved with correction, then additional magnification can be helpful. For example, an adult with 20/40 vision would benefit from a 50X telescope.
3. Brightness in daytime decreases dramatically above 25X for most adults with good or corrected vision. At a magnification of 50X, the image through a 56 mm objective telescope is roughly 1/4th the brightness perceived by the naked eye. At 80X, the brightness is about 1/10th that of the naked eye.
….
So, unless you have vision problems, magnification above about 17X-25X (depending on age) for a 56 mm objective rifle scope is not beneficial, and usually degrades the image rather than enhancing it."
So, above a magnification of roughly 21X, give or take, a 56 mm objective telescope is magnifying blur - it's not providing any more detail about the target to someone with good vision. Below that magnification, the eye is the limiting factor.
[Yes, the eye with better acuity sees the telescope-induced blur at a lower magnification, not a higher one]
If you have vision problems that cannot be improved with correction, then additional magnification can be helpful. For example, an adult with 20/40 vision would benefit from a 50X telescope.
3. Brightness in daytime decreases dramatically above 25X for most adults with good or corrected vision. At a magnification of 50X, the image through a 56 mm objective telescope is roughly 1/4th the brightness perceived by the naked eye. At 80X, the brightness is about 1/10th that of the naked eye.
….
So, unless you have vision problems, magnification above about 17X-25X (depending on age) for a 56 mm objective rifle scope is not beneficial, and usually degrades the image rather than enhancing it."
For a 50 mm scope, reduce all the magnification values above by 11%. So, for an adult with good vision, the optimum magnification for a 50 mm scope is about 22X.
When I look at these magnification values, I'm a bit astonished that the limits are so low. If 22X is the upper limit for a 50 mm scope due to physics, then why are there so many 50 mm scopes with 24X+ magnification out there from reputable companies like Leupold, Zeiss and Swarovski?
One reason is that there are a lot of shooters with poor vision. I'm reminded of this all the time at the range. Astigmatism is the most common problem. Remember that the diopter ring corrects for focus, but not astigmatism. If more shooters knew this, they would get their eyes checked and wear correction when shooting. Wearing glasses is a much better solution than buying a higher magnification scope.
Another reason is that we are all lazy. Why force ourselves to concentrate on features that are at the limit of our visual acuity, when we can simply boost the magnification and make those (blurred) features larger? However, the scope magnification is optimum when the eye can just begin to perceive the blur. The eye doesn't actually see more detail at higher magnification, and we pay for the higher magnification in terms of lower brightness and lower image contrast (due to higher glare).
Some compromise is OK. Up to about 3X loss of brightness in daytime is not a bad thing because your eye can quickly accommodate this change in brightness. Loss of image contrast is usually bad for hunting (because target features have low contrast to begin with), but it's more tolerable for target shooting (because man-made targets are usually high contrast). So, for strictly target shooting applications, one could argue that up to about 40X magnification for a 50 mm scope has some value because target details are a little "easier" to see (i.e., they require less concentration).
Personally, I set the upper limit at 25X for a 50 mm scope. Granted I have good vision and target shoot mainly to train for hunting. When I look at my stable of scopes, there isn't one 50 mm scope that goes above 25X. All my variable magnification scopes go down to at least 6X, which provides a wide enough field of view for rapid target acquisition.
Finally, I haven't included the effect of turbulence-induced blur on image quality. Turbulence, not the scope, is usually the limiting factor on image resolution in daytime, especially when looking over flat terrain on a sunny day. This is another reason why high magnification scopes have dubious value.
![a9cc6155-f27f-4013-830a-373fa278ce92_zps44fa0f82[1].jpg](https://r2d2.www.longrangehunting.com/attachments/38/38655-adfc4d2abb486d7fcb90f2c80ad64b75.jpg)
