Which is the best magnification for binoculars? 8x42 vs 10x42?
To present the same quality of the image, a 10x42 binocular needs to be a bit better than the 8x42. That sorta come with higher magnification: alignment tolerances are tighter, etc.
Assuming the overall image quality between an 8x and 10x are comparable, and especially if low light is in play, I would suggest choose a 10x50 instead of the 10x42. Also, there is technique involved, so if you want to use a higher magnification binocular handheld, a little experimentation and careful consideration of fit are important.
10x50 is usually a little heavier and longer which helps keep it steady. The lighter the binocular, the more hand tremor you will see. Same for the length. Longer is typically steadier.
When choosing 8x42 or 10x42 binoculars, the smaller magnification has a wider field of view.
In optics, the exit pupil is a virtual aperture in an optical system. Only rays which pass through this virtual aperture can exit the system. The exit pupil is the image of the aperture stop in the optics that follow it. In a telescope or compound microscope, this image is the image of the objective element(s) as produced by the eyepiece.
Exit pupil is very easy to understand. If you take the size of the front lens of the binocular (in millimeters) "42" for example and divide the magnification into it (lets say 8x) then you will have an exit pupil of 5.25 mm. This exit puil is the little ring of light that you see in the binocular eyepiece when you hold it out in front of you.
The larger the exit pupil then the more light can get to your eye through the binocular. That is why a lower powered binocular generally gives you a brighter image (when everything else is equal). However there is a bit more to it than just that. Our eyes can only allow so much light in...depending upon the size of our pupil (how much it is dillated). during the day time a large exit pupil on a binocular does not offer much advantage because our own pupils aren't open more than 4 mm. However, at dawn/dusk our pupils dillate much more and in that case a binocular with a larger exit pupil would give us a distinct advantage.
Having said that, the 8x42 would probably be the better option since it has an exit pupil of 5.25 as opposed to an exit pupil of 4.2 that is found on a 10x42 binocular.
In most binocular models, the eye relief is greater on the 8x42 version than on the 10x42 version or the 8x32 version is there is one.
Eye relief matters only to people who wear glasses. But if that's you, you'll want to pay special attention to the eye relief, especially when considering a 10-power binocular. For glasses wearers, 16 mm of eye relief is minimal, but it's better to get a binocular with 17 mm to 20 mm of eye relief.
It’s generally true that the more expensive, top-of-the-line binoculars have higher image quality and are also more durable. However, there are also a lot of cheaper binoculars that are adequately durable and have decent optical quality. Thus, pick a price range that you feel comfortable buying binoculars at and don’t feel compelled to go beyond it. Of course, 8x cheaper than 10x.
How To Choose ?
If you’re planning on scanning and following fast-moving and small targets.
if you need details for identification, need the extra reach with longer distances under good light.