Why is chromatic aberration purple?

Evelyna42 · 10-12-2019, 05:12 AM

Just a silly question that I'm wondering about at the moment. Why is chromatic aberration purple? Well, usually purple anyway. I guess I'm interested in the mechanics of it and can't seem to locate an answer. I understand why chromatic aberrations occur thanks to this article: https://www.photographytalk.com/chromatic-aberration-and-how-to-fix-it-in-photoshop-or-lightroom but it doesn't explain why they're purple.

Just wondering...not a crisis

VisualEcho · 10-12-2019, 08:41 AM

That's a good question. But in my experience CA is not only purple, it's magenta, orange, green, and cyan. I'm a shallow DOF whore, and pretty much all I use is 1.4 to 2.2, so I have to deal with CA a lot, and it's definitely different colors.

I believe the reason is that light has a spectrum of colors that when mixed properly aren't always able to seen, and it's literally the bending of this light by the lens (like a prism in sunlight) that causes the colors to split apart. It's a sharp bend, a sharp contrast, so the colors are sharp. At least that's what I've understood over the years.

I'll also say that my 200/2 is my favorite lens, I shoot it exclusively at f2 has almost no CA, which is fantastic. Really, it blows every other lens away in that regard, and in most others.

overcoil · 10-12-2019, 11:20 AM

Purple Fringing is probably the term you should use to research the phenomena.

10-12-2019, 05:12 AM	#1
Evelyna42 New Member 8 Rep 6 Posts Drives: BMW i8 Join Date: Sep 2019 Location: US iTrader: (0)	Why is chromatic aberration purple? Just a silly question that I'm wondering about at the moment. Why is chromatic aberration purple? Well, usually purple anyway. I guess I'm interested in the mechanics of it and can't seem to locate an answer. I understand why chromatic aberrations occur thanks to this article: https://www.photographytalk.com/chromatic-aberration-and-how-to-fix-it-in-photoshop-or-lightroom but it doesn't explain why they're purple. Just wondering...not a crisis
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10-12-2019, 08:41 AM	#2
VisualEcho Banned 6659 Rep 4,143 Posts Drives: '18 M2 6MT Join Date: Sep 2019 Location: Missouri iTrader: (1) Garage List 2018 BMW M2 [10.00]	That's a good question. But in my experience CA is not only purple, it's magenta, orange, green, and cyan. I'm a shallow DOF whore, and pretty much all I use is 1.4 to 2.2, so I have to deal with CA a lot, and it's definitely different colors. I believe the reason is that light has a spectrum of colors that when mixed properly aren't always able to seen, and it's literally the bending of this light by the lens (like a prism in sunlight) that causes the colors to split apart. It's a sharp bend, a sharp contrast, so the colors are sharp. At least that's what I've understood over the years. I'll also say that my 200/2 is my favorite lens, I shoot it exclusively at f2 has almost no CA, which is fantastic. Really, it blows every other lens away in that regard, and in most others.
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10-12-2019, 11:20 AM	#3
overcoil Major General 3121 Rep 5,582 Posts Drives: M235i 6spd Join Date: Dec 2013 Location: Mid-Atlantic iTrader: (0)	Purple Fringing is probably the term you should use to research the phenomena. Last edited by overcoil; 10-26-2019 at 06:45 AM..
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