Magnification increases the "brightness" of the image.
On 10X the hunter is "sort of" 10 times closer.
The best image will be at the max zoom that offers a bigger or equal exit appature to you eyes pupil.
Add in the better resolution of the large objective and a significant gain can be had in low light.
Image brightness is solely attributed to exit pupil size, up to the point that it matches the size of your own dilated pupil. If the exit pupil is larger than your own pupil, then you have effectively reduced the aperture of your scope. So yeah, in that sense the brightest image will be perceived when the exit pupil matches your own pupil.
But magnification on it’s own does not increase brightness. Only the size.
Although a point source of light won’t lose as much brightness as objects that are absorbing or reflecting light as magnification increases.
Many objects will disappear as magnification increases and the exit pupil gets smaller than your own. But given enough light to illuminate your target, you can perceive a sharper image down to about a 2mm exit pupil. Because this centers the light on the most sensitive part of the eye.
Although with a dilated pupil you may perceive more details with higher magnification, given enough light on the target, the image will begin to blur with an exit pupil much smaller than 2mm.
