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Old 12-01-2016, 11:34 AM
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Rigel003 (Graeme)
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Join Date: May 2006
Location: Adelaide, South Australia
Posts: 1,038
Thanks for the helpful responses. I guess the bottom line is that the actual diameter of the filter thread on the outside lens is in fact always larger than the real aperture (diameter) of the lens and this explains why the figures don't work out as expected. Yes Patrick. Good Point. I'm clearly not going to be able to use step down rings to get the 70 mm down to f4.
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