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Old 02-09-2009, 12:07 AM
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Starkler (Geoff)
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Join Date: Sep 2004
Location: Melbourne
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A few design parameters you need to decide on or find out are:

focuser max and min height
Tube diameter
Desired focal plane height from focuser top (Is this scope for visual or photography?)
size of fully illuminated field ( for secondary sizing)

The wider the tube and higher the focuser, the bigger the secondary is required.

The software David linked to is the standard and works well.
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