I heard some remarks from experienced hunters about scopes doing a good job at light gathering for late evening hunting. And some of my scopes do brighten up the scene a little bit. But my scopes are all garbage (took me a while learning this fact), none of them worth more than 200$. So, my question is, theoretically, if the scope has good light transmission with quality multi-coating, larger diameter of front lens and really low magnification (something like 3x-4x) would it be doing better job at brightening up the picture? What is the trick here
the "light gathering" question
- Thread starter 22lr
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larger objective lens, more light gets in the scope => brighter
less magnification = bigger "exit pupil" so in dim light when your pupils dilate the light coming out of the scope covers more of your retina => brighter
better coating, less light lost in the glass => brighter
less magnification = bigger "exit pupil" so in dim light when your pupils dilate the light coming out of the scope covers more of your retina => brighter
better coating, less light lost in the glass => brighter
All else being equal, better quality glass will give you a brighter image than worse quality glass.
All else being equal, better lens coatings will give you a brighter image than worse quality coatings.
All else being equal, lower magnification will give you a brighter image than higher magnification, up to a point.
All else being equal, a larger objective lens will give you a brighter image than a smaller objective lens, up to a point.
In the latter two cases "up to a point" will be the size of the exit pupil which is basically the size of the image being projected to the user's eye. The exit pupil is determined by dividing the objective lens size by the magnification, e.g. 50mm lens divided by 7x magnification equals approx 7mm of exit pupil. As a young adult the largest dilation of the dark adapted human pupil will be approx 7mm, and it gets worse (smaller) as we get older, with about 5mm being pretty good for a middle-aged person. If your scope is producing an exit pupil larger than your pupil dilates, it is a brighter picture, but the excess is wasted on you. (A larger objective lens may still be worth having to increase the field of view, but extra "light gathering" can become irrelevant.)
(So, now that I am 50, a 7x35 bino with its 5mm exit pupil will seem as bright to me as a 7x50 with the same quality glass and coatings, but if I had the same two binos to compare when I was 20 I ought to have been able to see the 7x50 was brighter because of its larger exit pupil.)
All else being equal, better lens coatings will give you a brighter image than worse quality coatings.
All else being equal, lower magnification will give you a brighter image than higher magnification, up to a point.
All else being equal, a larger objective lens will give you a brighter image than a smaller objective lens, up to a point.
In the latter two cases "up to a point" will be the size of the exit pupil which is basically the size of the image being projected to the user's eye. The exit pupil is determined by dividing the objective lens size by the magnification, e.g. 50mm lens divided by 7x magnification equals approx 7mm of exit pupil. As a young adult the largest dilation of the dark adapted human pupil will be approx 7mm, and it gets worse (smaller) as we get older, with about 5mm being pretty good for a middle-aged person. If your scope is producing an exit pupil larger than your pupil dilates, it is a brighter picture, but the excess is wasted on you. (A larger objective lens may still be worth having to increase the field of view, but extra "light gathering" can become irrelevant.)
(So, now that I am 50, a 7x35 bino with its 5mm exit pupil will seem as bright to me as a 7x50 with the same quality glass and coatings, but if I had the same two binos to compare when I was 20 I ought to have been able to see the 7x50 was brighter because of its larger exit pupil.)
Strictly speaking, no optic "gathers" light, they transmit light, and some light is always lost in this transmission.
The idea that low power scopes are the best performers in low light is also a bit of a myth. The highest power that still gives you the 5-7mm exit pupil, will be the optimum for any given scope. 8x56 scopes had a moment of popularity a couple of decades ago, and are still popular in Europe, because the high power with the huge objective lens make them awesome performers at last light.
The idea that low power scopes are the best performers in low light is also a bit of a myth. The highest power that still gives you the 5-7mm exit pupil, will be the optimum for any given scope. 8x56 scopes had a moment of popularity a couple of decades ago, and are still popular in Europe, because the high power with the huge objective lens make them awesome performers at last light.
this part I don't understand. Objective lens is much bigger than exit pupil, how do we call that if not gathering?
The bigger question for me though is - how much brighter the image can get in a good scopes, specifically designed for low light conditions? Is it worth the extra money invested?
brightness is only one aspect of the issue.
resolution and contrast and color rendition and purple fringing and image distortion also count.
high end optics allow more detail to be observed (all other things equal) so yes, it is worth the extra money
edit: for example I recently bought a Vortex Viper scope in the same parameters as my older Bushnell Elite 4200. Only the reticle is different.
The Viper is good but not nearly as good as the Elite. I can only imagine what a Swaro or IOR can do for way more money.
