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09-29-2012, 11:29 AM   #1
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wide open lens sharpness

are there any of the older pentax lenses , the K series or M or even A , in the 28mm to 85 mm range, that are actually sharp wide open? and which ones would they be ? thanks.

09-29-2012, 12:18 PM   #2
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QuoteOriginally posted by glinda Quote
are there any of the older pentax lenses , the K series or M or even A , in the 28mm to 85 mm range, that are actually sharp wide open? and which ones would they be ? thanks.
The M40 is sharp wide open, at f/2.8.
09-29-2012, 04:42 PM   #3
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I've had great results with the M 28mm f/3.5 wide open (and stopped down). It's got some serious 3D sharpness mojo going on.

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09-29-2012, 04:47 PM   #4
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M50/1.7, A50/1.7, and K55/1.8 are all sharp wide-open - and even sharper stopped down.

09-29-2012, 06:01 PM   #5
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QuoteOriginally posted by glinda Quote
are there any of the older pentax lenses , the K series or M or even A , in the 28mm to 85 mm range, that are actually sharp wide open? and which ones would they be ? thanks.
28mm to 85mm is a huge, huge range. I'm curious what application you have where you would be interested in the sharpness of such a wide range of lenses. Maybe if you explain further you'll receive better suggestions.

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09-29-2012, 07:54 PM   #6
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The K55/2 might be a candidate, because the difference between it and the K55/1.8 is a ring which permanently restricts the lens to f2. So it's technically wide open and slightly stopped down all at the same time.

Macro prime lenses should fit your description. They are designed to be well-corrected at all apertures, even wide open. Of course that means only f2.8 at best.

Lenses gets better stopped down. If you really need super sharpness at wide apertures, start out with a lens that's faster than you need, then stop it down. For example, I compared my Sigma 28mm f1.8 to a Pentax-M 28mm f3.5 mentioned above. At f2.8, the Sigma is sharper than the Pentax at f4. They look about the same at f5.6. Then the Pentax gets sharper at f8.
09-29-2012, 08:50 PM - 1 Like   #7
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Sharp is a relative term. Almost all lenses are sharper stopped down than wide open. The questipn os, how sharp do you need? And how wide oen do you need? Unless you are planning on making wall sized enlarge ents, chances are the zone of the picture that is actually in focus will be more than sharp enough for practical purposes with most primes.
09-30-2012, 07:01 AM   #8
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thanks, just thinking that using the Av setting on the camera with an older lens that is sharp wide open would be one way to have an almost automatic lens, most if not all , lenses i've tried seem to be only sharp after a few f settings closed down. then that negates the Av setting on the camera really. can use M obviously though. thanks again.

10-01-2012, 10:33 PM   #9
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Well, shooting wide open makes sense only if you really want paper-think DOF, thats a mh bigger issue than any small reduction in sharpness. Since you posted in the beginner's forum, I wonder if perhaps you are mistaking shallow DOF for softness?
10-02-2012, 04:45 AM   #10
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Take this with a grain of salt, but here are some test results from older Pentax lenses:

http://www.takinami.com/yoshihiko/photo/lens_test/index.html

The 50/1.7 formula (either the M or A version) does indeed have good sharpness even at the edges when wide open. Other notables (according to these tests) are the K28/3.5 and K35/3.5, both of which have a reputation for sharpness. He didn't test the older macros but given that they are a) macros and b) slow, I'd expect these to be sharper still.
10-02-2012, 09:01 AM   #11
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QuoteOriginally posted by baro-nite Quote
Take this with a grain of salt, but here are some test results from older Pentax lenses:

http://www.takinami.com/yoshihiko/photo/lens_test/index.html

The 50/1.7 formula (either the M or A version) does indeed have good sharpness even at the edges when wide open. Other notables (according to these tests) are the K28/3.5 and K35/3.5, both of which have a reputation for sharpness. He didn't test the older macros but given that they are a) macros and b) slow, I'd expect these to be sharper still.

Why with a grain of salt? You are perhaps too modest Sir! Or do you have reason to discount Takinami's data?

Dave in Iowa
10-02-2012, 09:11 AM   #12
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QuoteOriginally posted by newarts Quote
Or do you have reason to discount Takinami's data?
I don't doubt that he did his testing rigorously, only that any test regime has limitations. The usual caveat I've seen about this particular set of tests (a well-known set) is that some lenses get artificially high or low marks because of how contrast affects the test.
10-02-2012, 10:27 AM   #13
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QuoteOriginally posted by baro-nite Quote
I don't doubt that he did his testing rigorously, only that any test regime has limitations. The usual caveat I've seen about this particular set of tests (a well-known set) is that some lenses get artificially high or low marks because of how contrast affects the test.
There is also sample variation, the one you buy might not be as good as the one he tested or you might get a better one.
10-02-2012, 01:07 PM   #14
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this is a pretty interesting site one of you have referred me to- http://www.takinami.com/yoshihiko/ph...est/index.html
however, what are the various numbers representing? such as 62 at f 2 , etc ? thanks
10-02-2012, 01:57 PM   #15
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Explained here: http://www.takinami.com/yoshihiko/photo/lens_test/procedure.html

Each column of numbers is the resolution for a given aperture (f2, etc.) The top number in a column is the resolution at the center (higher = better). Going down the column, the measurement points move away from the center to the edges. The last number is the corner resolution.

Last edited by baro-nite; 10-02-2012 at 04:50 PM. Reason: typo
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