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Author Topic: Schneider digitar: is this some sort of chromatic abberation?  (Read 2587 times)

torger

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When I have made photos with out of focus backgrounds that have saturated colors in them with my 90 and 120mm schneider digitar lenses I seems to get colored bands/borders/outlines, like yellow in the attached picture.

I'm not sure what this is caused by. I suspected the raw converter, but I tried two including capture one and the same problem. There is no clipping in the raw file either.

Since I've only seen it when something is out of focus I'm suspecting that there is some chromatic abberation effect of the digitar standard lens designs (very simple designs). Normally I don't shoot with OOF backgrounds with these lenses of course, but with people in the frame or macro it happens.

Is anyone familiar with this problem or can make a guess what it is?
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torger

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Re: Schneider digitar: is this some sort of chromatic abberation?
« Reply #2 on: July 16, 2012, 07:09:09 AM »

Oh, I was probably not clear enough what the picture shows :-) It's a part of rainbow so those colors should be there, the problem is the bleak curvy light yellow band curling around in the crop (quite hard to see, requires good screen). I've already applied color cast correction.

The reason there's a rainbow in there is that the problem only seems to occur (become visible at least) when there's saturated colors in out of focus background

Here's another example, probably a bit clearer. Look at the out of focus features especially, there some red and greenish outlines around the violet out of focus flowers.
« Last Edit: July 16, 2012, 07:13:17 AM by torger »
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ced

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Re: Schneider digitar: is this some sort of chromatic abberation?
« Reply #3 on: July 16, 2012, 08:25:09 AM »

Downloaded your flower pic and try as I may can't find what you describe I think with a 90 & 120 it would be unlikely to get this kind of issue you describe wider lenses maybe.
Maybe those good lenses nabbed the borealis for you in the "rainbow pic"...
Try a neutral grey background and inspect if the problem is clearer.
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torger

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Re: Schneider digitar: is this some sort of chromatic abberation?
« Reply #4 on: July 16, 2012, 08:45:16 AM »

Once more :-), this time with an arrow pointing at the phenomenom.

I have other macro shots when this does not occur, it only seens to happens around saturated colors.

Large format digital lenses of the type Schneider digitar does is very simple designs and work great for the typical use case - whole scene sharp - but I was thinking that maybe there's some disadvantage of this design when there are oof backgrounds.

I can't remember I've seen this kind of phenomenom with my DSLR lenses, but then to safely check this statement I just went through a number of images and actually found the same phenomenom although in a smaller extent in one of my images shot with a Canon 50mm lens (which happens to be of similar design as the Schneider lenses though).

My guess is that it is some sort of longitudinal chromatic abberation that goes haywire around contrasty edges of saturated colors, and I just have to live with it or find some tool to clean it up. But it also might be some color space clipping problem so I just wanted to check if someone else is familiar with this, or if I have some issue with my post-processing toolchain
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theguywitha645d

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Re: Schneider digitar: is this some sort of chromatic abberation?
« Reply #5 on: July 16, 2012, 10:41:05 AM »

It is simply the rendering of the oof area--AKA Bokeh. It is quite common and increasing contrast in your image will emphasize it. This can be a factor of the spherical aberration in the system. There is not a lot you can do.
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EricWHiss

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Re: Schneider digitar: is this some sort of chromatic abberation?
« Reply #6 on: July 16, 2012, 01:55:10 PM »

Axial CA can be seen as green purple outlines in the out of focus regions near the areas in focus.   That said, I'm not sure this is what you are seeing and may just be bokeh as the above poster suggested.  Try shooting something thin and dark like a telephone or power wire over a white surface - just out of focus both in foreground and background and see what you get?
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BernieKohl

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Re: Schneider digitar: is this some sort of chromatic abberation?
« Reply #7 on: July 17, 2012, 04:15:52 AM »

I think what you are seeing there is probably colors canceling each other out in the out of focus area. The SK APO Digitars should not have any noticeable longitudinal or lateral chromatic aberrations.
« Last Edit: July 17, 2012, 04:21:14 AM by BernieKohl »
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ced

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Re: Schneider digitar: is this some sort of chromatic abberation?
« Reply #8 on: July 17, 2012, 12:19:06 PM »

Honestly I think you have a fixation on this phenomena it can be a difficult transition of one colour to another and can be exaggerated by the profiles display included.
As said before those lenses are not causing the problem.
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torger

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Re: Schneider digitar: is this some sort of chromatic abberation?
« Reply #9 on: August 21, 2012, 03:30:47 AM »

Okay, I eventually found the problem for this and it is a bit embarrassing *blush* -- I was not using my own computer and the screen I was using at the time had some specific color issues which causes some particular colors (greenish-blue, bright yellow, magenta) to be very much exaggerated leading to clear banding artifacts. So I was very surprised that noone really saw the to me very obvious color issues :-)

Now when I look at my pictures on my calibrated screen there is no problem... arrghhh! Sorry to have wasted your time guys!

Lesson learnt: never trust a screen which has not been calibrated.

There is some special problem with that screen though, because I've looked at several uncalibrated screens too and only that specific one I was using show this problem... that an uncalibrated screen can have a tint or some black crushing I knew, but this with a few individual colors being very much off while the rest is okay is new to me.
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Rob C

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Re: Schneider digitar: is this some sort of chromatic abberation?
« Reply #10 on: August 21, 2012, 03:56:34 AM »

Well, I'm delighted you found the cause because I was seriously concerned about my eyes, which I already know have a problem  - one - at least; I was afraid I discovered yet another!

Whew!

Rob C
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