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08-15-2013, 01:25 PM   #1
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resolution of the smc pentax 24 2.8 k lens

I am interested to hear other people's experience in testing this lens. Using the same set up as I would for testing usually, Edmund optics chart, film Tmax 100, good tripod etc, I just recorded 110lp/mm. As a reference, I get 60 to 67 lp/mm out of a Tamron SP 90mm using the same set up. This performance is simply astonishing. Anyone else seen similar with this lens? Its sharper than the Pentax M 28/3.5 I have by this measure.

08-15-2013, 01:54 PM   #2
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"Yoshihiko Takinami - K24/2.8 - very sharp, good color saturation/rendition, scarce distortion"

"
Yoshihiko Takinami - K28/3.5 is quite excellent, though there's . . . noticable light fall-off wide open, . . . I think K28/3.5 is best 28mm lens Pentax ever made because of its resolution, aberrations, color rendition, contrast, etc.[a more complete review from Yoshihiko, 7.16.99 . . .] The . . . K28/3.5 . . . is really excellent in performance, IMHO, and is very comparable in size and weight to M85/2. Yes, it seems a big lens for a usual 28mm lens. Whereas M28/3.5 is also an excellent performer and is comapct in size. Comparing the performances of the two, K28/3.5 is a bit better in point of corner resolution, light fall-off towards the corners, and the correction of spherical aberration and coma, IMHO."

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Yoshihiko Takinami Test Results
08-15-2013, 06:26 PM   #3
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how to mesured them??
08-16-2013, 02:59 AM   #4
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To measure this kind of resolution, you need a sensor which is capable of this, and decent light and a high contrast subject, then you need to be able to take information off the sensor...in this case I was just using TMAX 100, although some of the very high res films are capable of 400lp/mm from Adox. I am then inspecting through a Nikkor 50/2.8n enlarging lens at f4, using a 25x scope. I have been doing this a bit. Tripod stability and a serviced camera are also required, and I use a focussing magnifier. In this case, the distance to the subject was 3m which works out at about 125 focal lengths. The Edmund chart is better than stuff you can print yourself as it has a higher contrast ratio.

I posted this in part because I was surprised that it outresolved the Pentax M 28/3.5 which I had previously thought was immensely sharp.

I had previously seen claims on the web that this Pentax 24 2.8 was very sharp, but I was astonished to actually see the results.

Its amazing what this old technology is capable of.

08-16-2013, 03:31 AM   #5
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I haven't made any precise measurements. But at least I have all the lenses you compare and most of those Yoshihiko measured.
Sure, the K24/2.8 is very sharp, sharper than the M28/3.5, which isn't one of Pentax sharpest lenses. But the K28/3.5, K30/2.8 and K35/3.5 is sharper than the K24/2.8. At least my copies. The K24/2.8 is also supposed to be sharper than the older design of the K24/3.5 (but that's a lens I don't have).
In my experience, the K24/2.8 remain sharp in the center at all apertures if you close it to f5.6. To get sharp corners you need to close to f11.
The K28/3.5 and K35/3.5 are very sharp from center to corners from f5.6. The K30/2.8 already from f4. It is an extraordinary lens in that sense.
The M28/3.5 does OK in the center, but never gets really sharp in the corners. The M28/2.8 is slightly better, but not as the K-generation relatives.
Of all these lenses, would I have to pick one, I would pick the K30, if I would have to pick two, I would pick the K24/2.8 and the K30 (even though the K28/3.5 is sharper than the K24, but given I have the K30, the K28 is too close).

Last edited by Douglas_of_Sweden; 08-16-2013 at 08:56 AM.
08-17-2013, 01:34 PM   #6
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This is interesting, thanks. I will have to seek out the K 28/3.5 now!
08-17-2013, 06:02 PM   #7
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QuoteOriginally posted by whojammyflip Quote
Anyone else seen similar with this lens?
In practical use, as opposed to formal lab testing,
it seems quite sharp in the center,
and does well at closer distances.
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