Rich, If you look at the mathematics of the situation, you'll find that there is little you can do (read nothing) to improve an image by placing an obstruction in the light path. Doing so ALWAYS degrades the image. The Goodwin Mask is an obstruction. An apodising mask is an obstruction. An off axis aperture stop is an obstruction. The secondary is an obstruction. The spider is an obstruction. ALL of these things degrade the image, assuming you have a decent mirror in the first place. (If you don't, get it re-figured!) Now, all that being said, sometimes you can degrade the image in just the right way to allow you to see one part of the image a bit better. Double star observers do this by using square masks, apodising masks, and other "tricks" to move the light away from the airy disk in just the right way to see a secondary star. By doing this, however, the overall image always suffers. An obstruction is an obstruction is an obstruction. It doesn't matter where it is in the optical train, if its there, you'll see the effects of it. If its sitting on the mirror, its still many, many wavelengths of light away from the mirror, and it effects the light both coming and going. A spider at least only has one go at the incoming light. Brent --- Richard Tenney <retenney@yahoo.com> wrote:
--- Chuck Hards <chuckhards@yahoo.com> wrote:
It makes no difference if the obstruction is high in the tube, or at the mirror's surface.
Chuck,
Are you saying that unless one is splitting double stars, it is highly unlikely that any increase in image sharpness or quality will be realized with such a mask for planetary viewing? (it's all just imagined, or is simply a result of better collimation)?
Rich
__________________________________________________ Do you Yahoo!? Yahoo! Tax Center - forms, calculators, tips, more http://taxes.yahoo.com/
_______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com
http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy __________________________________________________ Do you Yahoo!? Yahoo! Tax Center - forms, calculators, tips, more http://taxes.yahoo.com/