[house]

Spent half an hour shooting charts with some of my comparable, mostly vintage, lenses. The results largely match my experience from just shooting the lenses but the curves can clarify some behaviour. I've used the free mtfmapper software that was used to calibrate the Perseverance rover cameras. I've shot an A1 size chart to minimize error. MTF mapper download | SourceForge.net

Do note that these are only relevant to my particular copies of the lenses and K-1. I have made effort to avoid mistakes but it is a home setup not a proper lab.

Pdf files and the various charts can be downloaded here https://filebin.net/squipa562ph8p2qu this link will expire eventually.

I'm not focussing on wide open as that's not my main use case.

SMC Pentax-FA 50mm f1.4 vs SMC Pentax 55mm f1.8 vs SMC Pentax-DA 50mm f1.8
Interestingly the K 1.8/55mm behaves very well. The FA 1.4/50 curves look a bit odd so I wonder about misfocus. The DA shows clear signs of being optimized for apsc.



The K 1.8/55 has better CA performance than the FA 1.4/50. Note the 4 vs 1.5 in the colour key.


HD Pentax-FA 35mm f2.0 vs SMC Pentax-DA 35mm f2.4 AL
Here the DA cleans up a little bit better when stopped down.



SMC Pentax 28mm f.35 SHIFT vs SMC Pentax (K) 28mm f3.5 vs Vivitar (Komine) 28mm f2.8 MC Close Focus Wide Angle
Here the K3.5/28 shines and the 3.5/28 shift reveals why it has such peculiar performance.



F11 CA comparisons between the two K 28mm. Note that the shift graph goes to -8!


SMC Pentax-D FA 100mm 2.8 macro wr vs SMC Pentax-M 100mm f2.8 vs SMC Pentax (K) 135mm f3.5
I've previously made side by side photos that revealed much the same as below. The macro suffers from a lot more CA as well. The M 100mm is a great performer that is rarely talked about. for non macro it beats the dfa100 macro.




F8 CA comparison. Note numbers in the key, the colours aren't directly comparable. The macro has *a lot* worse CA, not that the graph goes to 4.

---

Last edited by house; 02-13-2022 at 08:49 AM.

[ProfessorBuzz]

This must have been a ton of work. Any way to get a readable version of the graphs? I tried zooming, but the legends and numbers can't be read.

[house]

This must have been a ton of work. Any way to get a readable version of the graphs? I tried zooming, but the legends and numbers can't be read.

It's not really a ton of work. You just open a buch of files and the software creates lots of info. I have 3d grid mtf's and CA graphs as well. Just from one click. The software helps with aligning the camera as well by giving you precise pitch, yaw, rotate error.

I have pdf's but not sure where to upload yet.

The curves are 10, 30, 50 line pairs red,blue,green respectively. The forum software scaled the images down unfortunately.

---------- Post added 02-13-22 at 06:27 AM ----------

This must have been a ton of work. Any way to get a readable version of the graphs? I tried zooming, but the legends and numbers can't be read.

I added a link to pdf downloads in the first post.

[c.a.m]

Edit: damn that medium density fiber board headline... can't fix it...

LOL. I've been doing some projects around the house. When I first read the heading, I wondered why someone on PF is comparing construction lumber.

Thanks for posting your results. Your findings about the Pentax-M 100/2.8 are interesting. I have always been happy with my sample of this lens.

- Craig

[UncleVanya]

Edit: damn that medium density fiber board headline... can't fix it...

Go advanced in the editor.

[ProfessorBuzz]

I added a link to pdf downloads in the first post.

Thanks for the PDFs.

What's the S vs M in the line legend? I'm just learning how to interpret these graphs.

[house]

Thanks for the PDFs.

What's the S vs M in the line legend? I'm just learning how to interpret these graphs.

Sagittal and Meridional. Meridional values are read along lines that go like spokes in a wheel. Sagittal are read like concentric rings. (my simple explanation) Here are some resources at various levels.
Lens Rentals | Blog
How To Read An MTF Chart

Detailed
Lenspire

When the Sagittal (solid lines) separate from the Meridional (dashed lines) you have astigmatism. See the 28mm shift above. The lens is sharp for verticals but soft for horisontals, sort of as it actually depends on where in the frame we're looking.

[whojammyflip]

This is great. Its interesting to see the performance of the 55/1.8, the 28/3.5 and the 100/2.8. They all display flat curves as they get stopped down, with the uncertainty bands tightening up.

I tested a boat load of lenses about 3 years ago using MTF Mapper:
MTF Mapper - PentaxForums.com