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Old 11-10-2019, 01:16 AM
ngcles's Avatar
The Observologist

ngcles is offline
Join Date: Dec 2006
Location: Billimari, NSW Central West
Posts: 1,641
Stick with what you're got

Hi Kevin & All,

Originally Posted by cometcatcher View Post
Keep the SCT. No affordable refractor will come close to it.
Succinct and perfect advice.

Your 28cm Schmidt-Cassegrainian is approximately equivalent to a 23cm refractor for visual use that would be prohibitively expensive (for 99.5% of the population). It will require a costly, gigantic mount with a tall pier capable of supporting an approximately 60kg payload and will not be, by any reasonable use of the word, portable. It will probably require a dedicated observatory building to be reasonably usable.

Just to address the second part of your question about magnification. The magnification a telescope provides is calculated by dividing the focal length of the 'scope by the focal length of the eyepiece. For example your C-11 has a fl of 2800mm and when used with a 20mm fl eyepiece, provides x140. A 28cm refractor with a 2800mm fl gives exactly the same magnification with the same eyepiece. A larger telescope or a different design of telescope does not by itself provide more or better magnification. Any telescope can be made to magnify any amount you want simply by putting in a shorter focal length eyepiece.

"Magnification" by itself is no a way to describe the performance of a telescope. There is a practical limit to the amount you can apply on a given night depending on the design of the 'scope, the quality of the optics and most importantly the the atmospheric stability (seeing). For a 28cm Schmidt-Cassegrainian it will be about x500 in the very best conditions imaginable. A 28cm refractor will allow a bit more than that, but again the conditions must be perfect. The major limiting factor on 98% of nights is the atmospheric seeing that will force that high-magnification limit downwards significantly.When viewing a planet, you are better off with a smaller, brighter, sharper and stable image than a big, fat, wobbly blancmange induced by using too much magnification for the prevailing conditions.



Last edited by ngcles; 11-10-2019 at 01:40 AM.
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