Quote:
Originally Posted by Quark
Hi Derek,
I have no idea regarding F ratios - someone once told me how to calculate but I have forgotten.
If you know reply and I will do my homework!!!!!!!!
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Hi Matt,
There is a most helpful article in the Projects & Articles section here on IIS, by Anthony Wesley "How to calculate focal length from plate scale"
http://www.iceinspace.com.au/63-386-0-0-1-0.html
If you do this then by dividing the the calculated focal length by the dia of your aperture you will get the your focal ratio.
Regards
Trevor[/QUOTE]
Thanks Trevor - my focal ratio is 500mm (focal length) / 60mm (diameter) = 8.33. I do use a 2.5 Powermate too!