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I have a Canon 700d with a supported lens (24mm EF-S)

Peripheral illumination is ON in the camera menu, but chromatic abberation fix is OFF. Why is that?

Why would I ever want it off?

Or to put it in another way, how do I know when to turn it on or off? Am I supposed to shoot a photo, look at the LCD, decide that the correction is needed, enable it and then shoot again?

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I have a 650D and I am pretty sure the 700D would have a similar issue I have noticed with enabling jpeg correction. Basically, if you shoot just raw you will get a burst of 6 pictures before you experience any slow down. If you switch to shooting jpeg+raw you get different results based on the correction you have turned on. With both off you can take 3 pictures in a burst before you get a slow down. However, if you have correction for chromatic aberration AND peripheral illumination on your burst drops down to 2 pictures before you will experience any slow down. If you have peripheral illumination on OR chromatic aberration correction on you can take a burst of 3 pictures before you experience any slow down. I decided I like having a larger burst. If you are using software like photoshop or Lightroom there is a good chance you can correct both in post-processing.

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Vignetting correct is virtually lossless and quite predictable. So one can easily reverse it and there is little to no possible side-effect. That is why it is on by default.

Chromatic aberration removal on the other hand involves automatic detection and then replacement of suspected aberrations by colors from adjacent pixels. No only can it cause loss of details but the process is also not reversible. That is why it is off by default.

For completeness, there is one more correction which is available on some cameras and must be off by default. That is distortion correction. This is the worse kind of correction to do automatically because it affects framing. When barrel or pincushion distortion is corrected, part of the image gets cropped and you can easily end up with the edge of something or someone clipped even if you saw in the viewfinder. In those cases it would be best to do manually some correction but not do it fully to preserve the image.

Most times you can do those corrections later in software which is the safe thing to do. One would do it in the camera to save time but at the risk of some occasional mis-corrections.

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  • CA is not fringing. CA can be removed by scaling of the colour channels, which doesn't seem very dangerous. – ths Sep 7 '15 at 15:41
  • Actually, they are taken as one. Canon's page says Chromatic aberration, or color fringing, a common pitfall of digital photography where all colors are not focused through the lens at the exact point on the camera's sensor, can be corrected at the time of shooting with the Lens Aberration. The location of aberrations is therefore scene-dependent. – Itai Sep 7 '15 at 16:22
  • Scene dependent? Really? I can see how it might be focusing distance dependent but I always thought that after that it is indeed just a matter of a very slight difference in magnification for the different color channels. Admittedly scaling an image up and down by a certain factor will involve interpolation and thus resolution loss on the order of at most a pixel. Is that really so bad? – Floris Sep 7 '15 at 16:30
  • I don't see where the "therefore" follows from the quote, on the contrary, it can be removed because it isn't scene dependent. The fringing described in the answer is purple fringing, which is a completely different effect. – ths Sep 7 '15 at 16:52
  • No, it is scene-dependent because pixels are illuminated from light at different depths which have different angles of incidence which is what causes depth-of-field. In order to undo chromatic aberrations you have to know where each light ray comes from to know by how much colors diverge at each pixel. For fringing, it occurs in areas of high contrast, which should be obvious that is scene dependent too. – Itai Sep 7 '15 at 19:24

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