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12-10-2008, 03:52 PM   #1
Pentaxian
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Which sharp lens on extension tubes?

Regarding these charts ---

pentax M f1.7 50mm photo - steve flynn photos at pbase.com

pentax M f2 50mm photo - steve flynn photos at pbase.com
--- can someone confirm that the dashed lines show the contrast?

First I assumed the solid lines to show the contrast but that would have made the M 50/2 a better performer at f/4 than the M 50/1.7.

What do the solid lines show? Regarding these, the M 50/1.7 has a pretty pronounced "depression" in the region that corresponds to the corners of an APS-C image circle.

A quick way to compare two charts is to place two browser windows on top of each other, align the chart axes and then keep flipping between the browser windows using the keyboard.

Interestingly, the Rikenon 50/1.7 seems to be very close (and sometimes better) than the M 50/1.7

The Pentax A 50/1.7 seems to be slightly sharper than the M 50/1.7 (Measured Resolution Numbers). Is that true in the real world as well?

I'm interested in a sharp lens to be used with (Auto K-mount) extension rings. I've read that the 50/1.4's are not ideal for this because of their field curvature. But perhaps this doesn't matter except for copy applications (flat subjects)?

12-10-2008, 07:56 PM   #2
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What are you going to use it for? I use my M 1.7 together with extension tubes for cataloguing fishing flies. Absolute sharpness may not be critical for me but I think the result is good enough. The first photo is an example of a fly and the second I think you will recognise.





Try to borrow a setup before you decide. These photos are quite old and taken with the ist*DL

Cheers
Eddie
12-10-2008, 09:07 PM   #3
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This is from a full frame Pentax 6x7 negative shot with the M50/2.
Personally, I don't think it's going to matter much which lens you choose.

12-14-2008, 06:55 PM   #4
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Original Poster
QuoteOriginally posted by mingdie Quote
What are you going to use it for?
Nothing specific. Just close up shots in general.
The subject <-> lens distance will probably be too short to do bugs.


QuoteOriginally posted by mingdie Quote
I use my M 1.7 together with extension tubes for cataloguing fishing flies.
Nice shot. Looks very sharp (even oversharpened?) to me.
I tried to go fishing a couple of times in NZ but without any luck so far.

QuoteOriginally posted by Wheatfield Quote
This is from a full frame Pentax 6x7 negative shot with the M50/2.
Looks very good as well.

QuoteOriginally posted by Wheatfield Quote
Personally, I don't think it's going to matter much which lens you choose.
Why is that? Shouldn't it matter how sharp and contrasty a lens is?

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