UV and Circ. Polarizers can cut down on Purple Fringing CA?

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Mar 18, 2011
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New York City
I hate CA. I know you can remove it in Lightroom but sometimes, its not all removable without it affecting overall image quality in certain situations.

It's an eye sore for me and can ruin a photo to my eyes.

I know that you can avoid it by not shooting in harsh light with strong contrast areas and by stepping down the lens.

However, sometimes I want to shoot in harsh contrast and sometimes I want the DoF effect of a wide open aperture.

I've been reading however that UV filters such as the haze 2A and perhaps even circular polarizers might mitigate this effect. Is this true, bs, nobody really knows?
 
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I have never used a UV filter, and consider them 100% snake oil. I almost always use a CP, as I'm usually shooting cars, and have never found it to cure CA.

The best tool I have found to deal with CA is Nikon's Capture NX2, I use it exclusively for CA removal, as Photoshop and Lightroom simply don't cut it.
 
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Decided to go out and do my own test to find out for myself...

Camera is a Sony A850 shooting Adobe RGB cRAW with auto white balance and DR level 3. Everything else set to standard or normal. I'm using a brand new Sony Zeiss ZA 85mm F1.4 without the hood to make it easier to quickly change filters.

All shots were taken seconds within each other although not on a tripod.

I took two shots one at F1.4 an one at F2 in aperture priority mode. No post editing was done besides cropping.

I used the Hoya UV HMC Super UV(0) filter which is made in Japan. I also used the Carl Zeiss Sony Circular Polarizer T*. Both were 72mm. I picked this UV filter because it won #1 in UV blocking according to Lenstip. When adjusting the polarizer, I did so until the sky looked darkest.

I misfocused on the circular polarizer shots however for the type of test here, it seems to make minimal difference.


Here is the scene:
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Here it is without any filters cropped first at F1.4 and then at F2.

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Here it is with the Hoya HMC UV Filter at F1.4 and F2.


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Here it is with the Sony Zeiss T* Circular Polarizer at F1.4 and F2.


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Combined view at F1.4

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Combined view at F2

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Conclusion:

None of the filters seem to make an appreciable difference in reduction or changing the nature of the chromatic aberration.

On the positive, the filters don't seem to increase in an appreciable manner within the margin of error for this test any chromatic aberration.

Keep in mind, sharpness wasn't the test, the test was for filters affecting PF. Focus was a bit sloppy.
 
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Joined
Aug 25, 2009
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Missouri
Ah, I understand now. I wonder, my 200/2 has almost no CA, is that because I'm shooting at f2, the lens construction itself, or because of the longer focal length?
 
Joined
Feb 1, 2011
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Boston
Chromatic Abberation is caused by dispersion in the glass. White light consists of the entire rainbow. However, the index of refraction of the glass is different for each color -- therefore the each color is "lensed" or affected differently by each lens element. We often see blue fringing or red fringing because they are at the edge of the visible light spectrum. Lenses for our dslrs are designed so that they are balanced for the rainbow.
Does my explanation make sense?
I would not expect a CP to fix CA. Flat optical elements (such as UV haze filters or CPs) should not change the CA you see. If you get a cheap non-achromat "close-up filter", it should make the CA worse.

Hope this helps.
 

Growltiger

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Apr 26, 2008
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When using a Nikon camera, this is a good reason to either take JPGs or use Nikon View NX2 or Nikon Capture NX2. In fact for me it is the most compelling reason to process photos in this way.

In all three cases the CA is automatically removed. Both versions of NX2 describes it as "Auto lateral color aberration", and it works like magic.

If you use the Adobe products for RAW processing you can remove it, but it requires manual adjustment.

(I really can't see why adding a filter would help.)
 
Joined
Jan 15, 2008
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CA is more or less present due to lens construction. Some desings produce more, some less.
The faster a lens, the more CA will exist. This CA can be corrected to certain degrees. The more CA is corrected, the harsher oof areas/boke will be.
Are you sure you are not mixing up longitudinal chromatic aberration (purple/green fringing) with spherical aberration?

Longitudinal chromatic aberration (purple fringing) does not affect the quality of boke (nor does lateral CA). Chromatic aberration can be "fixed" in lens design by using apochromatic glass.

Spherical aberration is a major ingredient for creamy smooth boke, and it does not cause CA or bring CA with it. SA can be "fixed" with aspherical elements, but Zeiss (and Leica too) use aspherics much less than Canon/Nikon, because their philosophy is to produce smooth boke and that signature spherical aberration "glow."

Typically spherical aberration is "good" for portrait lenses, but chromatic aberration is bad for all lenses.
 
Joined
Mar 18, 2011
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As far as CA goes, it's unavoidable in any lens design that is fast and sharp with acceptable bokeh. For the subject at hand, that was completely uncorrected in LR, I'm sure its pretty acceptable with some correction.

For those wondering about the performance of this lens, the following were post processed but not much if any effort was spent removing any CA... I do think I need to play with the AF fine tuning of this lens though if I am going to use it at F1.4 frequently.

The most noticeable CA to me is by the top of the lamp post and some surrounding the tree.

The following were shot wide open at F1.4

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_DSC1593.jpg by jaetography, on Flickr

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_DSC1580.jpg by jaetography, on Flickr

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_DSC1597.jpg by jaetography, on Flickr

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_DSC1696.jpg by jaetography, on Flickr


The following at F2:

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_DSC1684.jpg by jaetography, on Flickr

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_DSC1702.jpg by jaetography, on Flickr

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_DSC1701.jpg by jaetography, on Flickr


The following at F2.8:


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_DSC1726.jpg by jaetography, on Flickr

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_DSC1687.jpg by jaetography, on Flickr

View attachment 906866
_DSC1690.jpg by jaetography, on Flickr

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_DSC1585.jpg by jaetography, on Flickr

And one handheld HDR.

View attachment 906872
_DSC1631_2_3.jpg by jaetography, on Flickr
 
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