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05-10-2018, 11:32 PM   #16
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Big aperture lenses have a long light path and the rays get a bit lost when used much closer than designed. I know that this lens doesn't work as well as a real macro lens for very close work such a scanning negatives. At the distance you are using this might be a factor.

05-11-2018, 01:48 AM - 1 Like   #17
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QuoteOriginally posted by clicksworth Quote
Big aperture lenses have a long light path and the rays get a bit lost when used much closer than designed. I know that this lens doesn't work as well as a real macro lens for very close work such a scanning negatives. At the distance you are using this might be a factor.
I doubt if distance is much of a factor here. In the 1960s I did a lot of close work with the 55mm SuperTak on a set of extension tubes, and got impressive results.
But flatness of field and the mid-field dip in resolution is a factor in faster lenses. The later 50 f1.4 has impressive central sharpness, but it really dips between center and edge, while the 1.8 and later 1.7 are better in this regard.
This can be seen using the lenses on digital in live view for focusing, using focus mag and trying to focus off center. In mid field you can't get as sharp a focus as center, showing itís not field curvature but resolution dip.
05-11-2018, 04:19 AM   #18
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QuoteOriginally posted by stevebrot Quote
Well, I guess you have it pinned down, though your mirrorless camera does have a shutter and rock solid is always relative in the world of tripods, particularly when using the center column as a horizontal arm. Leveling the camera for copy work generally requires a small carpenter's level at the lens front bezel and is a pain without a geared head. Sorry if that sounds snarky, but I have done a fair amount of lens testing and copy work and that sort of thing is a common source of poor results. Assuming the setup is rock solid and true to the subject, three more questions:
  • How sharp and/or contrasty is the sheet music? Is it an original or a photocopy? I was struck by the low contrast.
  • Are you certain your adapter positions the lens at right angles to the sensor. I don't use your tools, but have read multiple reports of adapter issues that include poor alignment.
  • What is the physical condition of the lens? Specifically:
    • Is there evidence of internal fungus, crazed rear or internal elements due to botched cleaning
    • Is there evidence the lens has been subjected to amateur service? (This would include scratches on or around screw heads or bunged screw heads.)
It is quite likely that your lens has a problem traceable to physical damage and/or foreign substance on the optical path. The image of the staple at center (point of focus?) on the f/5.6 example was my first clue. It simply looks yucky. The ST 50/1.8 is a very fine lens and while it a bit of an antique, it is not a macro lens, and has some field curvature, it is still suitable for general copy work. Below is a test image I did with my ST 50/1.8 and a setup similar to yours.*


Pentax K-3, 1/10s, f/5.6, Super-Takumar 50/1.8, in-camera JPEG (highest quality)

The full-resolution JPEG may be downloaded (12.5MB) from: https://farm1.staticflickr.com/953/40211014180_d5c9a7de2f_o_d.jpg

Here is a full-resolution snippet from near the bottom edge of the APS-C frame



I deem the results adequate and much better than what you got from your lens, though if I were working from RAW, I would have applied a little sharpening and correction for the very slight chromatic aberration present towards the edges. If I were to do it over, I might also give it at least an additional 1.0 stops exposure and a tweak to white balance, but I was in a hurry. If it were a copy for my own personal purposes, I would also be at f/8 to defeat whatever field curvature might be lurking.

Since your lens is new to you, I might suggest contacting the seller.


Steve

* Subject (back of computer power supply box) on floor, natural window light, Giottos 9360 tripod with center column configured as horizontal arm, focus using magnified live view.
Hi Steve, thanks for your input! What aperture did you shoot this photo at? Your lens is a really good copy. I am making a separate post with my conclusions.
Alex

---------- Post added 05-11-18 at 04:46 AM ----------

I would like to thank everybody who shared their thoughts on sharpness issue with my lens. To really resolve it one needs a service manual for Takumar lenses to understand the logic of this lens servicing.

On Monday I bought parts Takumar 55 1.8 off ebay for $10 and when it arrived yesterday I tested it and found that its sharpness is way better than my original lens. I thought, OK I am going to take lens element/pack out of this parts Takumar and put it in mine. When I did this and tested my original lens with the new lens pack I realized I am seeing the same out-of-focus pattern as before. I decided that the mounting of the actual lens inside the lens housing and/or incorrect amount of torque of the screws may cause the problem. Moreover I realized that the screws that attach lens pack to the lens body and the screws that attach the focusing ring to the brass helicoid do affect lens sharpness and 'decentering' directly. When I tightened focusing ring screws some more WHILE the lens pack was already attached to the lens body I saw that the image became very sharp all around edges and there was a very soft spot right in the center of the image. Slightly decreasing torque on the focusing ring screws corrected this right away.

So Instead of fixing my original takumar, I harvested whatever parts I needed from it and fixed my parts lens and I am quite satisfied with it. However my lens produces evenly sharp image across the frame only when it is stopped down to f5.6.

Case is closed!

Thanks everybody!
Alex
05-11-2018, 08:11 AM   #19
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QuoteOriginally posted by cameracravings Quote
Hi Steve, thanks for your input! What aperture did you shoot this photo at? Your lens is a really good copy. I am making a separate post with my conclusions.
Alex
As noted in the comment...f/5.6, the same as your test photo. Mine is in EX condition, but excellent performance from the ST 55/1.8 and the successor Pentax-K 55/18 is the norm and was well-known when the lens was new.* Your original lens has problems and probably should be returned had problems and probably could have been returned.


Steve

* I have two and both are excellent performers. The other is an early version probably dating 6-8 years before the one used for the photo.


Last edited by stevebrot; 05-11-2018 at 08:17 AM.
05-11-2018, 04:03 PM   #20
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QuoteOriginally posted by stevebrot Quote
As noted in the comment...f/5.6, the same as your test photo. Mine is in EX condition, but excellent performance from the ST 55/1.8 and the successor Pentax-K 55/18 is the norm and was well-known when the lens was new.* Your original lens has problems and probably should be returned had problems and probably could have been returned.


Steve

* I have two and both are excellent performers. The other is an early version probably dating 6-8 years before the one used for the photo.
Indeed, Steve, your Tak is an excellent performer! And mine turned into an excellent organ donor. And I made myself a perfect 55 1.8 ST out of the two for about $25. This is not a bad price at all given that when buying old lenses one does not really know what he is buying until the lens can be tested.
Cheers
05-11-2018, 05:20 PM   #21
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QuoteOriginally posted by cameracravings Quote
Indeed, Steve, your Tak is an excellent performer! And mine turned into an excellent organ donor. And I made myself a perfect 55 1.8 ST out of the two for about $25. This is not a bad price at all given that when buying old lenses one does not really know what he is buying until the lens can be tested.
Cheers
$25 for the total is good indeed. Enjoy your "new" lens.


Steve
05-12-2018, 04:56 AM - 2 Likes   #22
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I shot this with my 55mm @ f/1.8 on my Canon 80D.

The plane of focus with this lens is quite thin wide open and I found that testing sharpness from the center to the edges is rather difficult wide open, everything needs to be set up, lined up, and just perfect towards an extremely flat surface. (as with all testing with fast lenses). One can sometimes take 5 shots with the same set up and get 5 different results when pixel peeping. The slightest vibration can change the conditions and results of the test shot.

Absolute and extreme sharpness isn't a deal breaker to me with these old lenses as they most often can create some amazing and artistic images....especially this 55mm Tak.
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