Kenko Extension Tubes Min. Focus Distance Test

Started Mar 23, 2013 | Discussions thread
Michael T
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Re: Kenko Extension Tubes Min. Focus Distance Test
In reply to rrr_hhh, Mar 23, 2013

rrr_hhh wrote:

Thanks for this test, very interesting. I have just ordered a set of those tubes from a China dealer, but I will have to wait for about two weeks before I get it.

Do you think that one could use the 75mm with the ose tubes to reproduce 24x36mm slides ? Since the reproduction factor is approximately 0.5 I hope so !

I haven't tried that but from my test target, I guess it roughly cover about 36mm width edge to edge.

Using the formula explained there above the purple flower, I have computed that the 26mm extension should result in a magnification of 0.45, which you are more or less confirming (the original magnification of the lens, plus the length of the tubes divided by the focal length of the lens, aka 0.1+26/75).

Yes, I calculate the same way, so should be 0.45

Any remarks concerning IQ when using the two rings together ? Any corners vignetting ? Any adverse effect on the sharpness of that lens ? And how many F stops are you loosing ?

I don't see any deteriorate of IQ, sharpness and vignetting.  But I am not doing pixel peeping so may be I do not see any problem.

I have not do any accurate measurement, but from my limited usage time so far, f lose roughly 1.5 stops all together, this includes lose due to the tubes and lose due to closer focusing distance block the light.

Michael

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