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Explaination Of 100% Cone?

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Posted by Martin on May 21, 2001 13:36:39 UTC

Thanx for looking in to my scope Walter! I didn't realize that a larger secondary would give me a larger illuminized field of view by the 100% cone. After reading your thread I looked into Newt a little clooser and that gave me some answers :) I can kind of guess what the difference is between the 100% cone and the 75% cone but I'm not exactly sure.
Could you explain it to me?
Allso Newt says that the secondary should prefferably be below 20% the size of the primary. making the mirror over 2" would make it bigger than that. So does that mean that there is no "Best" way to size the secondary?

Meaning that I will have to choose between having a large field of view illuminised by the 100%cone or having a sharp immage and not missing the gathering light that will be lost by the secondary blocking the primary.

By the way, how much loss of contrast will there actually be if I make the secondary mirror bigger than 20% of the primary.
Before I thought that the only thing that matters is to get the secondary as small as possible.

//Martin

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