I have continued to gnaw at this, and I'm now in trouble with my wife. I've spent all day on it. She insists I stop.

I tried many things: spherical lenses, elliptical lenses, flat lenses, displacement, bump, normals - in so many combinations it would make your head spin. Remember there are two lenses, three surfaces. The number of combinations possible is ridiculous.

I have managed to hit upon an arrangement that gives almost no distortion even at great magnification. However, it introduces some new problems I'll have to work out. 

So I'm leaving you with just this progress report. I am going sailing tomorrow so probably I won't do any more until Monday.

I am at such high magnification that aiming the scope is now extremely difficult. I have had to switch from one pawn to a ring of them to help me orient myself, and I had to use point-at to line up. Even then, the numerical errors require tiny adjustments (thousandth of an inch) in the point-at position in order to compensate for Poser's numerical errors.

This render is showing the targets at a distance of 1000 yards. That's right - 1000 yards, 3000 feet, 914.4 meters.

If I showed you the target rendered without the scope, you wouldn't see them at all. They don't even fully occupy one pixel. Even against a plain black background it's extremely hard to make out where they are without the scope.

You might think I'm done then. Nope - now I can't get the scope to show the target (even at lower magnification) unless the camera is almost perfectly lined up with the scope. 

I'll keep at it.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)