Hi, I just wrote:
>I compared the resulting exposure times of the Rubinar and the Tokina AT-X
>150-500mm at 1:5,6 and 500mm. The time was circa 1/10 times longer with the
>Rubinar, which may be a result of the lower light transmission of mirror
>lenses. So the effective aperture is maybe (say) 1:5,7 - 1:5,8.
What I wanted to say, is that the exposure time with the Rubinar was longer
equivalent to 1/10 aperture.
Matthias
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