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07-02-2012, 01:50 AM   #1
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Cromatic Aberration- who is at fault, camera or lens?

I know a lot of lens have this problem. But how much can be put on the lens and how much on the camera?

This question came to mind when the k-30 is supposedly designed to reduce CA.

07-02-2012, 02:56 AM   #2
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Isn't the K-30 supposed to reduce CA in the AF sensor block? This causes shifts in focus due to different lighting conditions (like indoors incandesant light).

Apart from that CA is a function of the lens itself. However the body can influence how much the CA shows up - due to sensor pixel size (smaller pixel size show more pixels of any CA present).
07-02-2012, 04:36 AM   #3
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Chromatic Aberration or CA or purple fringing is a problem related to light as it passes through the lens glass. Essentially the light breaks apart in to its various colors (the light as it passes through the lens elements is bent differently depending upon its color makeup - think of light passing through a prism into the light spectrum of colors - same effect), and these colors are focused at different distances as they hit the sensor. Some of the colors are focused in front of the sensor, others perfectly on the sensor and some focused behind the sensor. Hence an image suffering from CA appears to have its colors somewhat misaligned. The solution is to add glass that addresses this breaking apart (referred to as dispersion) of the light (of its various frequencies - i.e., colors). That is where apochromatic lens design and low dispersion glass (and other low dispersion materials such as fluoride) come in to play. All of this adds to the cost of the lens.To answer the question, I do not see how the camera design itself can correct this. The normal approach is both through the design of the lens and/or post processing.

07-02-2012, 05:49 AM   #4
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QuoteOriginally posted by Culture Quote
This question came to mind when the k-30 is supposedly designed to reduce CA.
In body JPG compression will quite often apply a number of processes to the image before saving it, one being CA reduction. Maybe this is what you're thinking of.

07-02-2012, 06:32 AM   #5
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QuoteOriginally posted by Culture Quote

This question came to mind when the k-30 is supposedly designed to reduce CA.
Like said i think you mean the AF system, that now has special elements that reduce CA just like some lenses have.

Anyway CA is always lens related but some can make it more visible then other, think for example about AA filter on the sensor that's different but the difference shouldnt be world changing if you even see it.
07-02-2012, 10:12 PM   #6
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OK. Because my Tamron AF 70-300mm F/4-5.6 Di LD Macro is giving me headaches with CA.

I have a couple of times seen CA with my M50, but the shot was on a high contrast subject on a sunny day. So I just wanted to ask to be sure.
07-03-2012, 05:32 AM   #7
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If you want to know more.

Chromatic aberrations
07-04-2012, 12:00 AM   #8
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QuoteOriginally posted by Anvh Quote
If you want to know more.

Chromatic aberrations

Thanks.

07-04-2012, 03:31 PM   #9
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QuoteOriginally posted by Culture Quote
OK. Because my Tamron AF 70-300mm F/4-5.6 Di LD Macro is giving me headaches with CA.

I have a couple of times seen CA with my M50, but the shot was on a high contrast subject on a sunny day. So I just wanted to ask to be sure.
That lens is a CA machine! Actually I think the lens is pretty sharp but CA is so bad that most of the shots looks a bit blurry just because of the undefined "colorful" edges.
07-05-2012, 06:15 AM   #10
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Refractive lenses always have chromatic aberration. As mentioned above, it is possible to minimize it with careful glass selection. However, it never totally goes away--it just becomes more or less acceptable. The only way to truly (and easily) eliminate CA is to use mirrors instead of glass.
07-05-2012, 07:08 AM   #11
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Since CA is far more pronounced on digital cameras, It's possible that some changes in sensor design could minimize it. I can never remember hearing much mentioned about it back in the film days. The route the camera and lens manufacturers have taken is to taken is to sell new "made for digital" lenses. A lot of editing software easily removes it so it's easy to come to the conclusion that the camera manufacturers could do the same thing in their JPEG processing but why would they? They are in the business of making and selling lenses as well as cameras. I suspect that most of their profits come from lens sales as the camera body market is cutthroat. Stopping down just about eliminates it. One thing I have noticed is that adding a TC makes it worse. I have put my Pentax A converter on lenses that normally have little to no CA and had quite a bit with the TC added.
07-05-2012, 07:16 AM   #12
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Teleconverters add distance from the lens to the sensor. I assume that since CA is the different wavelengths of light being split by a glass element, adding distance to the sensor will increase the effective distances between the wavelengths of light as they hit the sensor.

I'm not sure that CA is "far more pronounced" on digital cameras. That is more likely purple fringing or sensor bloom... they did make apochromatic lenses back in the film days.
07-05-2012, 09:32 AM   #13
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It's easier to look closely at a digital image then film and also digital does capture more details when we compare colour film with RGB sensor, black and white is a different story but with that we don't really see CA.

Here they also show CA with film (last photo), so it isn't a digital thing.
Chromatic aberrations

QuoteQuote:
Purple fringing: lens or sensor?

Chromatic aberration, and purple fringing in particular, have received considerable attention with the advent of digital cameras. Indeed, although chromatic aberrations can be noticed on film, they do look more intense on CCD or CMOS images. On the one hand the digital photographer is only a few mouse clicks away from a full screen display, and few lenses stand image inspection at high magnification. On the other hand it is possible that digital imaging somehow renders the color fringes due to chromatic aberration more distinct. One of the proposed mechanisms is an enhanced spectral sensitivity in the (ultra)violet and (infra)red regimes, where lenses tend to be poorly corrected for chromatic aberration. Purple fringing is often blamed on sensor bloom, which is odd as blooming is a quite different phenomenon. In fact, there are as many arguments against sensor bloom as there are in favor of chromatic aberration to account for purple fringing. The examples shown on the present page are all demonstrably due to the lens and not to the sensor. Sensor bloom has no known color preference, and if it had, it would not change its colors upon defocusing a lens or upon swapping lenses. The list of arguments is long.
07-05-2012, 05:55 PM   #14
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Yes, CA is definitely not limited to digital. For B&W film, it obviously wouldn't be noticeable per se, but would increase the total amount of aberration, adding to whatever "monochromatic" aberrations are present as part of the geometry. For color film, the dye layers added a slight built in correction since each layer was at a different focal plane. Same is true for the Foveon detector.
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