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Glass Mounted Secondary on Newts

Started by Bruce N., 04/24/2002 12:36AM
Posted 04/24/2002 12:36AM Opening Post
Why aren't there Newts with glass mounted secondarys like SCT's??? Wouldn't this eliminate the diffraction spikes??

Thanks from the Newbie

Bruce
Posted 04/24/2002 01:03AM #1
Yes, but there are also some reasons not to do it. One is that the diffraction spikes from a thin-vane spider don't really harm the image much. Another is that you can get rid of diffraction spikes with curved spider vanes if you really want to. Finally, if you don't want to degrade image quality by using an inferior glass, it can be expensive to use an optical window since the glass really needs to be multicoated for maximum transmission and reduced internal reflection (which would reduce image contrast and could drop the performance below that of a well-made Newt using a good spider).

It will work, however. Markus Ludes has a large Newt made for him by Aries that is designed this way, and I am sure it is great. For smaller scopes it seems a whole lot better to me to go with the Mak-Newt design since you get better image quality off-axis without a coma corrector.
--
Mike