Did a quick test with the OM extension tubes. With the 7mm one, the
maximum focal distance is 32 inches, which makes it roughly equivalent to a
+1.13 diopter close-up lens. For the 14mm the distance was 17 inches, making
it roughly equivalent to a +2.31 diopter close-up.
Given this, an expansion tube that would be equivalent to a +0.5 diopter
close-up would need to have a length of about 3mm, which simply is NOT going to
happen.
>
> I just received my two OM extension tubes in the mail, and tomorrow
>I should be able to post some results. Looking though all of the books
>that I have on nature and close-up photography I was not able to find
>any mention of how to calculate the maximum focal distance for a given
>extension, but I did find an equation to adjust the f-stop for a given
>extension. For 5mm you decrease by 1/3 and for 10mm you decrease by
>2/3. I was already familiar with the shutter speed adjustments between
>close-up lenses and extensions, so this was no great revelation.
>
Chris
When the going gets weird, the weird turn pro
- Hunter S. Thompson
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