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Old 08-08-2009, 04:14 PM
ausastronomer (John Bambury)
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Join Date: Mar 2005
Location: Shoalhaven Heads, NSW
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Quote:
Originally Posted by Kirkus View Post
If I'm imaging a planet at prime focus with, let's say a scope with a FL of 750mm, would the image be twice as large using a scope with a focal length of twice that -- 1500mm?
Yes that is correct. A scope at prime focus with a focal length of 1500mm will give double the image scale of a scope having a focal length of 750mm. A 2X barlow in a scope of 750mm focal length will achieve exactly the same result of doubling the image size.

Cheers,
John B
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