I'm looking to upgrade to a spotting scope that is capable of seeing a 5.56 hole at 600 yds. I have looked at many posts here and other places and can't find anything that positively answers that question. Any help would be very much appreciated.
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That's really a great answer with respect to exit pupil size. I hadn't thought of that...Do some research on the subject of 'Exit Pupil'.
This is a dimension that is derived by dividing the objective lens diameter by the power of the magnification being employed.
For example, a 60mm objective being divided by a 30x magnification derives an exit pupil diameter of 2mm.
Now look in the mirror and estimate the diameter of your own eye's pupil. I can't tell you what that is, but I'm practically certain its quite a bit bigger than 2mm.
That's not good. It needs to be bigger, maybe as much as twice or three times bigger, in order to deliver enough light to allow the entire retina to process the image.
Now you can decrease the magnification by a factor of two or three, using a 15x or a 10x magnification.
That's not terrible, and when mirage runs strong, 15x may not be such and unreasonable upper magnification limit.
But it also makes it maybe more difficult to justify some of the optical system currently in use.
This a very great oversimplification, and should lead to some discussion to follow.
A 5.56 hole is just about 1/4MOA in diameter. A healthy unaided eye is assumed for argument's sake to be able resolve (yes I can see it/no I can't see it) an object 1MOA in diameter. So just to be able to discern the 5.56 hole at 100yd, you need a 4x, and at 600, you need a 24x, but that exit pupil (let's say 4mm for a ballpark value) needs to be 4mm x 24x magnification, deriving a 96mm objective.
Rephrasing, that's a 24x96 scope. Just to be barely at the minimal limit of being able to see/not see the hole.
Wow. Just wow! Maybe this goal is impractical.
Greg