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Secondary Size

Started by ccwoodruff, 03/20/2009 12:18AM
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Posted 03/20/2009 12:18AM Opening Post
Chris Woodruff
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Join Date: May 2001

Location: Valencia CA, US

Posts: 99

I need to replace the secondary on my 12.5" f4.1 newt. The tube diameter is 15". I know there are programs I can use but I get confused :-) I am trying to cover as close to a 35mm ccd chip as possible without the secondary getting too big. If someone could give me a rough estimate that would be great!
Thanks!
Chris Woodruff
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Posted 03/20/2009 12:38AM #1
dan hilts
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Location: Oshawa ON, CA

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How far above the tube is the focal plane? (How tall is the focuser?)

dan
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Posted 03/20/2009 12:57AM #2
Jon Isaacs
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Location: San Diego CA, US

Posts: 2161

Hi Chris...

I happen to have my 12.5 inch F/4.06 setup in Newt for Windows, it has a 3.1 inch secondary. I modified it a bit for your situation. With a tube that has a 15 inch outer diameter and a focal plane which is 2 inches from the tube, (this means a super low profile focuser for most cameras), the fully illuminated diameter is 23.5 mm, the 75% illuminated diameter is over 50mm.

I suggest downloading Newt for Windows, fooling around, posting your results and asking some questions.

Jon
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