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Old 20-10-2013, 11:49 AM
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RickS (Rick)
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Join Date: Apr 2010
Location: Brisbane
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Steve,

One good way to find out your true focal length is with plate solving. The focal length specs for most scopes are a rough approximation.

The effects of an AO or filters should be negligible (these should be designed to have zero power) but flatteners, reducers and barlows will certainly have a significant effect.

You'll find a formula for the CFZ and a calculator here:
http://www.wilmslowastro.com/software/formulae.htm

The CFZ is dependent on wavelength (which is why CCDAP gives you different values).

Cheers,
Rick.
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