James Fusco said:
I'm posting this question here because I have not found a straight answer. Testing a lens with high magnification untill the image breaks down, this limit is it a test? Does this indication a quality of optics or design. ... My impression is magnification will increase error. Error of what, in what I do not know.
Hi. In the strictest sense of the word, I don't think this is a test. I'd classify it more as a general performance test. That is, all other things being equal, 2 identical scopes on the same night on the same object, but one with a better corrected lens, the one with the better corrected lens should achieve higher magnifications better. Not only color correction though, but spherical as well. Once the design corrects the color sufficiently, then the better spherical correction should allow you to use higher powers more effectively -- until you hit other barriers, like the atmosphere and all the many less than well understood things it does to the optical path.
At least, this is my understanding.
However...in practice, I have seen what you say. Generally each telescope I have they tend to have their own general limit for the average day. Further, the limits are different in terms of x/inch for each.
Finally, as far as observational experiences, even though there is the general truism that as you push mag, at some point it becomes empty mag as no new details are revealed just bigger image, I have recently poked a hole in that concept. Several weeks ago I decided to push and push magnification on the Moon and do some detailed observing. What I discovered was interesting...even at rediculous magnifications, while I did of course get to a point of losing details, in other places more details did indeed reveal themselves! I went up and down in powers on the particular spot where I noticed it happening and what I "think" was probably at work was how contrast is related to resolution. So as I pushed the mag and the image got dimmer, lower contrast details started to wash out then disappear all together. However, in very high contrast areas, whose brightness was extreme, more details popped up. So what I learned for me in this exercise, that you will miss new details if you are looking at a high contrst object and you never go past that point where you start to see a general fading or softening of detail due to supposedly excessive magnifications.
Anyway, the reason you've probably not found a straight answer on this is probably because there is none?! 8O But the fun is in the experimenting