| jcjr |
| (professor emeritus) |
| 05/22/08 04:32 PM |
|
Re: Strange Results in Eyepiece FOV Comparisons
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Quote:Quote:
All else being equal (regarding resolution from center to edge, contrast, transmission, color purity, etc...), if I had the option to see a real field of 77 degrees within an apparent field of 68 degrees, vs. seeing a real field of 77 degrees spread over an apparent field of 82 degrees, I would choose the former, since my eye would be able to take in the same real field of view far more comfortably, with less wandering of the eye required to absorb the exact same chunk of sky.
You would rather have -11.7% angular magnification distortion than +6.1%? OK, I guess maybe I can see that, but where do you draw the line? How about an RFoV of 400 degrees in an AFoV of, say, 50. Of course there's a teensy bit of negative angular magnification distortion there, only about -700%, but it fits a lot of sky in 50 degrees! How much is too much?
Mike, there is an application where maybe that would be very desirable. I wonder if you have ideas if it has been done or could be kludged together (it would probably require more than just the eyepiece)--
I think it would be great to have a largish crosshair finder scope with good light-gathering, and maybe a 20 or 30 degree 'quasi-fisheye' true FOV. The eyepiece view would be close to rectilinear in perhaps the middle 20 degrees of the apparent field of view, where the crosshairs meet. But the view would get progressively wildly distorted/compressed toward the edges.
Why? Well, with a TFOV that wide, you could point the scope 'in the ballpark' of the target, then easily find the target in the distorted periphery, and then easily guide it into the crosshairs.
True fisheye's are near 180 degrees, which would be unnecessarily wide and make it difficult to see the tiny points of light. But a 20 or 30 degree telescopic fisheye might be VERY useful as a Finder?
I got a nice SV F80 Finder because it hurt the bones groveling on the ground to sight thru a Red Dot. But even with about 5 degrees of FOV in the F80, I STILL have to grovel on the ground to sight along the tube, because 5 degrees is often too narrow a capture range to 'just aim in the general direction' and find the object in the eyepiece.
A TFOV of 20 or 30 degrees should eliminate groveling on the ground to sight along the tube, even if most of the view is extremely distorted.
Anybody ever made a Finder like that? Any ideas how to make one?