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What makes digital cameras more prone to suffer from chromatic aberration than film cameras?

I've read this at many websites, but the explanations differ, from what I think less credible explantions like "the digital cameras high resolution makes it more prominent" to more credible-sounding ones involving colour filters in front of the sensor creating another source of aberration in addition the what the lens has already produced.

Is there any truth in the statement in the first place, and if so why is that the case?

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Provide a source, else this sounds like a silly myth. It's the lens that causes chromatic abberation, not the sensor. There are some issues due to the Bayer matrix, but I wouldn't call those "chromatic abberations". Chromatic abberations are caused when the lens focuses different wavelengths of light differently. –  Olin Lathrop Feb 24 at 22:43
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I can't provide the exact sources where I originally read about it (It was a while ago), but a quick search for it gave loads of similar results: 1 2 3 4. It may very well be a myth as I wrote in the question, but if so it's widespread –  Hugo Feb 24 at 23:08
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maybe because film camera photos were mostly viewed at 15x10cm light reflecting prints in cosy light, where the viewer had the big picture in mind, while virtually all digital photos are anally inspected closely for errors at 100% "crop" on 15-25inch light emitting monitors or 30-50 inch TVs? –  Michael Nielsen Feb 25 at 20:44

3 Answers 3

up vote 3 down vote accepted

Obviously, chromatic aberration is created by the lens, and the amount of CA is the same.

However, film as a medium and the sensor respond a bit differently. True perpendicular light is handled in a similar way in both, but angled light meets a different surface when using film and when using a CMOS sensor.

CMOS sensors have tiny lenses over the color filter (see here), and it is pretty hard to provide a uniform group velocity inside a small lens for all kind of light wavelengths, so these create an angle-dependent and wavelength-dependent response to arriving light. (Consider white light going through a prism - same effect).

A film has much less sensitivity to incident angle. So you will just photograph the CA.

On the other hand, R, G and B coming from an angle will see different sensor sensitivities (each is different) than RGB coming perpendicular to the sensor. So that will show up as color shift or color change, making CA worse.

Well, this is the explanation I can think of for your question.

(And a good test would be to use directed white light on a CMOS sensor, and make photos starting from perpendicular and then tilting it more and more. I would expect a bit of color shift. But do not try this at home :-) ).

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There is also the rather thick (~1mm or so) antialiasing/UV/IR filter glass that sits directly in front of the sensor. In the corners of the sensor, incoming light will hit at an acute angle (unless the lens is telecentric) and this can do nasty things to the colours. Especially on say some Leica M-mount wideangle lenses where a small-diameter rear element is deeply recessed into the, well, not the "mirror house" but the corresponding cavity in the camera, close to the film plane. This doesn't happen with film. Microlenses can only do so much to overcome this. –  Staale S Feb 25 at 18:57

this due to way color are extracted from sensor. Only few digital camera truely see in color (the old sigma foveon is one of them in large "public" SLR). The sensor only see intensity of light so "black and white" and a front grid with colored filter is used to, later in the process, try to define teh original color. (see bayer's grid and their evolution) (sample of bayer application) Due to this interpretation, some situation give the wrong color as deduction. This happend often at the egde of sharp surface.

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Can you please elaborate and or provide some sources to why this results in colour fringing? If this is the reason it seems to be unrelated to chromatic aberration. –  Hugo Feb 25 at 9:05
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Also note that the way the Bayer sensor works is closer to the way the human eye works than Foveon! By this standard, humans don't see in color either! –  mattdm Feb 25 at 9:18
    
I recommand this article that explain how it append phaseoneimageprofessor.wordpress.com/tag/bayer-pattern (not reinventing the wheel). You could also look at wiki pedia for foveon that partially explain also (advantage of foveon on this issue) en.wikipedia.org/wiki/Foveon_X3_sensor. @mattdm, right eye work more like bayer but dispersion of eye unit sensor are different than a "regular" bayer grid, also each base unit capture different information where bayer/sensor capture the same filtered so aberation is not handle the same way by the brain. –  NeronLeVelu Feb 25 at 10:43
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This explains how a Bayer sensor can cause a certain class of color errors, but I wouldn't call those errors chromatic abberation as was asked in the question. –  Olin Lathrop Feb 25 at 14:49

I don't think any of the possible reasons you have read are wrong, as such. Certainly, the majority of the reasons in the links you provided seem plausable enough causes of a small amount of chromatic abberation.

Things like wonky lens elements and other manufacturing issues aside, the sheer complexity of modern lenses compared to those in the days of film and the addition of micro-lenses on the sensor will all contribut to the colour fringing you see. Increased resolution, as daft as it sounds, does highlight imperfections in many lenses, and frankly I don't think it's possible to study a print anywhere nearly as close as you can with a large screen at 100% zoom.

As nice as it would be to say that there is a specific reason why film is better than digital in this regard, it seems that it's actually a combination of many smaller factors.

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You are wrong. Expectations got nothing to deal with it. Chromatic aberrations ARE more pronounced on digital than film. It can be measured. One of such attempts was made by genotypewriter: secure.flickr.com/photos/genotypewriter/6147351879 - result being quite obvious: Film wins when it comes to CA. –  MarcinWolny Feb 26 at 9:06
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Altered my answer to remove my last comment. On my phone so I'll read the links later - in the mean time I'll take your word for it. :-P –  Thomas Bisset Feb 26 at 9:55

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