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Author Topic: Correcting geometric distortion on shift lenses -Contax Yashica 35mm PC-distagon  (Read 1301 times)

ryanwicks

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I picked up this lens recently to fill the void between my Canon 24mm TSE and 45mm TSE. It performs brilliantly in regards to sharpness, corner to corner, and colour rendition. However, it does produce noticeable barrel distortion when shifting, getting worse towards the edge of the image circle. How can I correct this uneven barrel distortion in post?
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marc aurel

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I picked up this lens recently to fill the void between my Canon 24mm TSE and 45mm TSE. It performs brilliantly in regards to sharpness, corner to corner, and colour rendition. However, it does produce noticeable barrel distortion when shifting, getting worse towards the edge of the image circle. How can I correct this uneven barrel distortion in post?

The distortion of the PC-Distagon is not simple barrel distiortion but a more complex "moustache" distortion which makes it difficult to correct. But:

Alpa offers a free plugin for photoshop that can correct distortion for a lot of shift lenses. Results for the PC-Distagon 35mm are perfect. You just have to choose the profile and enter numbers for the amount of vertical and horizontal shifts. Can't recommend it enough. Great service from Alpa.
Download here: https://www.alpa.ch/de/artikel/alpa-lens-corrector
« Last Edit: February 06, 2017, 06:06:28 AM by marc aurel »
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ryanwicks

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The distortion of the PC-Distagon is not simple barrel distiortion but a more complex "moustache" distortion which makes it difficult to correct. But:

Alpa offers a free plugin for photoshop that can correct distortion for a lot of shift lenses. Results for the PC-Distagon 35mm are perfect. You just have to choose the profile and enter numbers for the amount of vertical and horizontal shifts. Can't recommend it enough. Great service from Alpa.
Download here: https://www.alpa.ch/de/artikel/alpa-lens-corrector
The distortion of the PC-Distagon is not simple barrel distiortion but a more complex "moustache" distortion which makes it difficult to correct. But:

Alpa offers a free plugin for photoshop that can correct distortion for a lot of shift lenses. Results for the PC-Distagon 35mm are perfect. You just have to choose the profile and enter numbers for the amount of vertical and horizontal shifts. Can't recommend it enough. Great service from Alpa.
Download here: https://www.alpa.ch/de/artikel/alpa-lens-corrector

Thanks. I've looked at this before and can't for the life of me get the plug in installed. I'm on windows 10 and latest version of Photoshop CC. Anyway, I don't think it matters because I should have said, I'm using the 35mm PC-distagon on a Canon 5d and it looks like the Alpa plug-in only works with MF backs?
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marc aurel

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Thanks. I've looked at this before and can't for the life of me get the plug in installed. I'm on windows 10 and latest version of Photoshop CC. Anyway, I don't think it matters because I should have said, I'm using the 35mm PC-distagon on a Canon 5d and it looks like the Alpa plug-in only works with MF backs?

The Alpa plugin DOES work with full frame cameras. They have specific profiles for that. Used it succesfully with my 5DII, 5DIII, A7R, 5DsR.
But I can't help you with your installation problem (I use OSX). Maybe someone else?
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ryanwicks

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The Alpa plugin DOES work with full frame cameras. They have specific profiles for that. Used it succesfully with my 5DII, 5DIII, A7R, 5DsR.
But I can't help you with your installation problem (I use OSX). Maybe someone else?


Great, thanks Marc. I've found some more information that says the plug in only works with the 32-bit version of PS CC on Windows, so I'm downloading that now.
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BartvanderWolf

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Hi,

The general problem with (complex) symmetric distortions is that one needs to center the image on a larger canvas, before applying a generic distortion.

When you also use good panorama stitching software, like PTGUI, it can figure out and correct for very complex distortions automatically by adding a second, shifted, image. Then center on the original region of interest, and crop. This will use high-quality resampling, and can also run on 64-bit Operating systems, which may help if files become large ( >2GB).

Cheers,
Bart
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ryanwicks

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The Alpa plugin DOES work with full frame cameras. They have specific profiles for that. Used it succesfully with my 5DII, 5DIII, A7R, 5DsR.
But I can't help you with your installation problem (I use OSX). Maybe someone else?

I've got the software working but it doesn't look like there are profiles for Canon. Attached is their list of supporting backs.
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marc aurel

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I've got the software working but it doesn't look like there are profiles for Canon. Attached is their list of supporting backs.

Oh. It looks like they have changed their policy. In the former package there were support files for DSLRs too. Now they are gone. Sorry, I did not know that :(
Marc-
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kers

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    • Pieter Kers

In addition to Bart;
If you take a shifted shot, you should also know the optical center to later make a good correction.
You can do that to make an additional unshifted shot as a reference.
the distortion correction has to be applied to the image correctly positioned inside the image circle.
It is one of those things that make shifted lenses a bit less easy to use.
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Pieter Kers
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qwz

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Capture One has a option to manually add a shift value (in mm) and distortion map also shifted.
For barrel you simply use a distortion slider (for instance for Samyang T-S 24 it will be between 23% and 26%, depends on focus distance). For moustache type you have to find a profile within C1-embeded (using a shot of a wall with lines or something) and save all in one preset/style.

For Photoshop you need to extend canvas according to shift amount and use Lens Distortion filter, may be also with some profiles. Handy to record a Actions for all most used shift values.
But C1 way is much-much faster.
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BartvanderWolf

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In addition to Bart;
If you take a shifted shot, you should also know the optical center to later make a good correction.
You can do that to make an additional unshifted shot as a reference.
the distortion correction has to be applied to the image correctly positioned inside the image circle.
It is one of those things that make shifted lenses a bit less easy to use.

Yes, it takes a Pano-stitcher with good controls to achieve good results, like PTGUI Pro offers. For shifted images, using the full (or a partial) image circle, the 'Horizontal shift' and 'Vertical shift' control parameters take care of the shifts. If the shift amount is not known or noted, I then prefer to let PTGUI automatically optimize for the required amount separately, so with the other optimizations disabled. Once the optical distortion parameters are optimized for a given lens, those values can be stored and recalled for later use, without requiring too much additional info.

With 2 images with lots of details (e.g. the facade of a building), using a 50% overlap, most of the optical issues can be corrected. So if one image is the intended scene crop, then the other image is only used to offer optical correction clues.

But having to correct a lot of lens distortion, remains to be a sub-optimal approach.

Cheers,
Bart
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