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Nagler eyepiece for a Televue Genesis?

Started by hankbuck, 11/14/2003 04:25PM
Posted 11/14/2003 04:25PM Opening Post
Hello, all,
I recently purchased a 5mm Nagler, Type 6 for use in my 9.25 SCT and my Televue Genesis. Worked great in the SCT, but in my Genesis the pincushion effect (I guess that's coma) was horrendous! I exchanged it for a 5mm Radian, which works great. This was my first try at a Nagler, with it's 82 degree field, in the Genesis. Boy, was that a shock! Has anybody had a similar problem with this combination, or a reasonable explanation why it wouldn't work?
Thanks, David
Posted 11/14/2003 05:04PM #1
David,

I'm a little unclear on exactly what the problem was. "Pincushion" is a form of distortion, which is a problem with image placement. If you have pincushion, straight lines are bowed inward, and stars move in an odd and, to some, disturbing way as you move the scope.

If you correct for linear distortion (pincushion and barrel), you are left with angular magnification distortion. Round planets would look oblong near the edge of the field, and angular distances would change as you move toward the edge of the field. For astronomical use, you generally want to keep the angular magnification the same across the field.

Is distortion your issue, or is it star images near the edge of the field?

Clear skies, Alan