Trying to understand Sigma FP-Color Shading correction

[Chris DC]

Hi All:

I finally got some sun around home and tried out my newly acquired Sigma FP with my old Leica M39 LTM lenses made back in the 1950's; the 3.5cm. F3.5 Summaron and the 9cm Leica Elmar M39 lens.

Overall I am pleased with the results. Both lenses give interesting looking images and are plenty sharp in the center. The Summaron 3.5cm shows significant purple coloring especially in blue skies around the extreme left and right edges of the frame. I took a picture of a white wall and set a custom color shading setting for this lens. I needed to add(?) some red and some blue to get the white wall to be monotone but the correction is not perfect.



Then when shooting with the lens (3.5cm Summaron) I choose this custom color shading profile. In my view it is only marginally better. I suppose I'll have to play around more with settings. I wish the manual was more detailed in this feature.

Here are some shots with the Summaron and the 9cm Elmar. The Elmar has no edge color problems.






Lots of purple edges on the 3.5cm Summaron




Less purple edging when the sky is less blue




Less purple edging when stopped down too.




This is a white wall after selecting the custom color shading profile-Not perfect!

And here's the 9cm Elmar's performance:




9cm Elmar-A little vignetting but no color shift.




9cm Elmar does well on distance landscape shots.

Overall I am having fun and that was the point of this acquisition. The camera is neat and the EVF is very helpful.

I can say that the dust on the sensor is annoying and something I am not used to seeing. I've been an Olympus mFT for nearly 20 years and never once had to clean dust off my sensors. Oh well.



Anyhow, if anyone can chime in and explain the right way to use the color shading feature on the Sigma FP I will be grateful.



CDC

 

[David Kieltyka]

You might want to post this in the L Mount forum too. There's at least one FP owner who posts there regularly.

-Dave-

 

[Antone]

Or better yet, the Sigma forum.

 

[Chris DC]

I did post in the Sigma forum also.



CDC

 

[Travis Butler]

I did post in the Sigma forum also.

Wish I had some suggestions, but that's one thing I haven't played with; I prefer doing all the color work in post, where I've got full control over it.

 

[ProfHankD]

I needed to add(?) some red and some blue to get the white wall to be monotone but the correction is not perfect.

It never will be perfect. The color shading comes from dispersion in the microlenses; even if the main ray is directed to the sensel, different wavelengths aren't quite. The more the entry angle to the sensor differs from perpendicular, the worse this problem is. Thus, the shading is partly dependent on the mix of wavelengths in the scene (some of which are lost, but correcting by adding them in is wrong if they weren't in the scene to be lost) and partly dependent on things like focus distance (which changes entry angles).

I can say that the dust on the sensor is annoying and something I am not used to seeing. I've been an Olympus mFT for nearly 20 years and never once had to clean dust off my sensors. Oh well.

Benefit of the thick cover glass on MFT: it softens dust images by making a bigger, less-focused, shadow that spreads over more of MFT's smaller pixels. Their cover glass also causes CA, etc. Dust is annoying, but thinner cover glass is still a win...

Anyhow, if anyone can chime in and explain the right way to use the color shading feature on the Sigma FP I will be grateful.

Any simple model will be easy to apply, but somewhat wrong. You can't really correct for having various wavelengths miss the sensels, you can only make credible guesses as to what might have been present but wasn't recorded.

This is one reason I generally stay away from rangefinder lenses, cost being the other.

BTW, the smaller sensor size of MFT also means fewer strongly angled rays, so that helps avoid color shifts off axis. You can play that game too: shoot in APS-C crop mode. ;-)

 

[Chris DC]

Hi Travis:

I am enjoying the FP and love the ability to go small with the bare camera or add the viewfinder and handgrip if needed. I also like the ability to customize button settings though I have been spoiled by the shear flexibility and ergonomics of the Olympus EM1x I normally use.

That said, the FP is really fun to use and produces pleasing images.

As regards the vignetting and purple edges in blue skies with the 3.5cm Summaron, I think I will just learn to like the aesthetics. I would like to know a simple Photoshop or lightroom routine to subtract a vignetted red ring from those pictures that need it. I use the vignette slider in Lightroom with no problem but cannot see how to shift color in a similar localized manner. If you have a routine, let me know!

I just did a few more tests of shooting blue skies, and now gray skies, with the Summaron. If I keep the aperture at F8 or above, the vignetting and color shift is mostly absent. This does make sense as I believe the color shift arise from oblique light rays hitting the edges of the sensor.

Here are examples:






3.5cm Summaron-F3.5-No Color Shade correction




3.5cm Summaron-F8-No color Shade Correction

Quite honestly, when I turn on the color shading corrections I see subtle changes but no real improvement.

I suppose the only thing that surprises me is that the color shading feature built into the camera has only a minor effect. I expected to be able to make more of a correction. Maybe it is lens dependent.

Going forward, I will stop down the Summaron when doing landscape photos with sky, which I suppose I ought to be doing anyhow!.



Cheers!



CDC

 

[Chris DC]

Hi Hank:

Thanks for these insights. I do well recall that Leica indicated the need for special microlenses and lens specific correction routines for the M8 and later rangefinders. I also recall Olympus making a big deal about designing their 4/3 lenses to be telecentric and hence rather large.

I have long been using the old, large optically correct Olympus lenses on mFT and I suppose I have just come to expect largely aberration free images.

For now i will stop down the Summaron to F8 for landscape shots that have blue skies

CDC

 

[Travis Butler]

Hi Travis:

I am enjoying the FP and love the ability to go small with the bare camera or add the viewfinder and handgrip if needed. I also like the ability to customize button settings though I have been spoiled by the shear flexibility and ergonomics of the Olympus EM1x I normally use.

Yeah, I get you. My E-M1 II definitely has a better grip, and I really miss the ability to store up to 10 lens name/settings whenever I use another company's camera. OTOH, the small size is what drew me to the fp in the first place, I like the ability to switch out the grip for something else - and it doesn't look like a Big Serious Camera, which lets it pass in some venues that bar professional gear. When I rented the Nikon Z5 and Lumix S5, both of them got rejected by those places, and the E-M1 II has gotten tagged as well.

There's also some inertia involved; once I start using a camera, I tend to keep picking it up unless I've got a reason to pick up a different one.

That said, the FP is really fun to use and produces pleasing images.

Indeed. "Fun to use" really trumps most other metrics for me, as long as the base image quality is good enough; cameras I don't enjoy using don't get used, no matter how good the image quality is.

As regards the vignetting and purple edges in blue skies with the 3.5cm Summaron, I think I will just learn to like the aesthetics. I would like to know a simple Photoshop or lightroom routine to subtract a vignetted red ring from those pictures that need it. I use the vignette slider in Lightroom with no problem but cannot see how to shift color in a similar localized manner. If you have a routine, let me know!

I use On1 Photo Raw as my primary editor, and it doesn't have anything like that either. The best I can think of would be a custom mask with a feathered edge that you could save as a template.

I'm in a somewhat similar situation with my favorite OM 24/2.8; it never vignetted on M4/3, but it can be pretty noticeable on FF. Most of the time, at least I don't mind the look.

I just did a few more tests of shooting blue skies, and now gray skies, with the Summaron. If I keep the aperture at F8 or above, the vignetting and color shift is mostly absent. This does make sense as I believe the color shift arise from oblique light rays hitting the edges of the sensor.

Here are examples:


3.5cm Summaron-F3.5-No Color Shade correction

Yeah, that's definitely noticeable. I admit the colors don't bother me, but I'm a sucker for cobalt blue skies; some of my desert-ish shots in Nevada and Monument Rocks in particular.Quite honestly, when I turn on the color shading corrections I see subtle changes but no real improvement.

I suppose the only thing that surprises me is that the color shading feature built into the camera has only a minor effect. I expected to be able to make more of a correction. Maybe it is lens dependent.

Going forward, I will stop down the Summaron when doing landscape photos with sky, which I suppose I ought to be doing anyhow!.

Well, if you're looking for 35mm... I have to admit, I'm really liking how my OM Zuiko 35/2 performs on the fp, if you can find one for a reasonable price.

--
Flickr at https://www.flickr.com/photos/the_prof67/ Warning: Heavy Learning in progress.

 

[E Dinkla]

Hi Travis:

I am enjoying the FP and love the ability to go small with the bare camera or add the viewfinder and handgrip if needed. I also like the ability to customize button settings though I have been spoiled by the shear flexibility and ergonomics of the Olympus EM1x I normally use.

That said, the FP is really fun to use and produces pleasing images.

As regards the vignetting and purple edges in blue skies with the 3.5cm Summaron, I think I will just learn to like the aesthetics. I would like to know a simple Photoshop or lightroom routine to subtract a vignetted red ring from those pictures that need it. I use the vignette slider in Lightroom with no problem but cannot see how to shift color in a similar localized manner. If you have a routine, let me know!

I just did a few more tests of shooting blue skies, and now gray skies, with the Summaron. If I keep the aperture at F8 or above, the vignetting and color shift is mostly absent. This does make sense as I believe the color shift arise from oblique light rays hitting the edges of the sensor.

Here are examples:


3.5cm Summaron-F3.5-No Color Shade correction


3.5cm Summaron-F8-No color Shade Correction

Quite honestly, when I turn on the color shading corrections I see subtle changes but no real improvement.

I suppose the only thing that surprises me is that the color shading feature built into the camera has only a minor effect. I expected to be able to make more of a correction. Maybe it is lens dependent.

Going forward, I will stop down the Summaron when doing landscape photos with sky, which I suppose I ought to be doing anyhow!.

Cheers!

CDC

You could try it with applications like Cornerfix. Part of the problem is how to get a correct flat field image to use in an application like that. And the vignetting + color shift depends on both aperture and distance setting so you would need more flat field correction images. Not to mention different illumination spectrums encountered indoors and outdoors.

I have used Cornerfix and similar apps or image editor tools in reproduction photography were there are more stable conditions.


Met vriendelijke groet, Ernst
No photographer's gear list is complete without the printer mentioned !

 

[Chris DC]

I have noticed that the old 3.5cm F3.5 Summaron lens has lots of field curvature (I think) on the full frame FP. When I use it on a mFT crop sensor camera the results are quite good. I expect that correcting for the color shift in post-process will not really make this a stellar lens by modern standards.

Thus, I have decided to embrace its quirks and try other, physically bigger, more telecentric, wide angle lenses when I come across them in my travels (thrift stores, estate sales, etc.).

CDC

 

[Chris DC]

Hi Travis:

Thanks for the insights. I have pretty much decided to just embrace the flaws of these old lenses and always be on the look out for others, like the OM35mm F2. I know of a funky camera shop in Columbus, Ohio that has four OM35mm F3.5 macro lenses for a good price. These lenses are small and focus down to 1:2. Something like that might catch my fancy as I already have the OM to L adapter and the OM to mFT adapter allowing use on my Olympus bodies too.

It sounds like you have a collection of old OM lenses and are a path similar to mine but a bit further down the road

Cheers,

CDC

 

[Travis Butler]

Hi Travis:

Thanks for the insights. I have pretty much decided to just embrace the flaws of these old lenses and always be on the look out for others, like the OM35mm F2. I know of a funky camera shop in Columbus, Ohio that has four OM35mm F3.5 macro lenses for a good price. These lenses are small and focus down to 1:2. Something like that might catch my fancy as I already have the OM to L adapter and the OM to mFT adapter allowing use on my Olympus bodies too.

Do you mean 35mm focal length on the f/3.5 macro, or just OM "35mm film" lenses?

I've got the OM 50/3.5 Macro, and it's a very nice lens - also, much smaller than most macro lenses !

How much were they asking for them? Even if it's the 50/3.5, I like it well enough I wouldn't mind a spare copy.

It sounds like you have a collection of old OM lenses and are a path similar to mine but a bit further down the road

I like the OM lenses a lot; small, very nice mechanically. The OM 24/2.8 is one of my favorite lenses, period. I also have the 28/3.5, 28-48/4 (special for being really small, and pretty high quality for a film-era zoom), 35-70/4 (also pretty good quality, though I don't like it as well as the Minolta MD 35-70/3.5 Macro), 35-105 Macro, 50/1.4, 50/1.8, 50/3.5 Macro, 50/2 Macro (a cult classic for a good reason), 85/2, 100/2.8 (another special one - very small for its focal length and great IQ), 135/2.8, 135/3.5, and 200/5.

 

[Chris DC]

I mean the OM 35mm F3.5 macro. They were priced between $70 and$100.



Since I have a great MFT kit I plan to acquire vintage lenses as I serendipitously come across them. Hopefully some will need cleaning and then I will have a reason to take them apart!

CDC

 

[Travis Butler]

I mean the OM 35mm F3.5 macro. They were priced between $70 and$100.

A little expensive, but not too bad... you planning on going back for them? I can definitely recommend 'em.

Since I have a great MFT kit I plan to acquire vintage lenses as I serendipitously come across them. Hopefully some will need cleaning and then I will have a reason to take them apart!

Hah. Good luck with that.

Seriously, OM lenses in my experience are pretty darn robust mechanically, and I've never had one with internal haze/fungus/etc. The only one I've ever had that's been dirty was the 35/2, which was stored without caps and was pretty caked with dust; but it was all external, and cleaned off nicely.