Chroma Blur and Chromatic Aberration

Question

Level 1

6 points

Chroma Blur and Chromatic Aberration

This question isn't about a problem, rather I'm looking for a comfirmation.

According to reviews on my two lenses, they're supposed to suffer badly from CA, yet I can't see any evidence in Aperture. Apparently, the CA in these lenses is easily corrected via software.

Adjusting Chroma Blur doesn't seem to do anything after import to reveal evidence of CA.

Am I right in assuming that Aperture is correcting CA during RAW import and that setting Chroma Blur to zero won't reveal it?

iMAC 24", Mac OS X (10.4.10), 500 GB drive

Posted on Jul 10, 2007 3:43 PM

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Answer 1

Jul 11, 2007 1:49 AM in response to Rusty Rat

Chroma Blur is great to remove color noise in high iso images. It has no effect on chromatic aberration.

Lightroom and ACR have both dedicated sliders to remove chromatic aberration. There is also a tool inside photoshop (filters-distort-lens correction)

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Answer 2

PhotoRob

Level 1

0 points

Jul 11, 2007 4:19 AM in response to Eduardo Calvo

hi eduardo

as i understand your an expert on aperture. perhabs you can help me too.

i know APERTURE quite well but i can't figure out this: how can i change the text layout? i'm looking for a button or so to center the text or have it all on the left or right.

thanks for helping! rob

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Answer 3

jrg_uk

Level 3

720 points

Jul 11, 2007 5:06 AM in response to Rusty Rat

Another thought - sometimes what appears to be chromatic aberrations is actually an artifact of the sensor capture/decoding (see http://wiki.panotools.org/Chromaticaberration#What_it_isnot).

So Aperture may be doing a better job of lessening that effect - otherwise often seen as purple blooming - than whatever the reviewers used when they did their testing.

I'd stick with what you see with your camera, and your lens, rather than worrying about what any random third party reviewers might say.

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Answer 4

Rusty Rat Author

Level 1

6 points

Jul 11, 2007 7:20 AM in response to jrg_uk

Not concerned about it, so much as curious as to why the CA (toward the yellow end) showed so distinctively in the lens test and is absent in my images. If Aperture is handling it automatically, I'm a happy camper. In the lens test, the author mentioned that it was easily fixed via software.

When I checked for CA (actually TCA) I was looking more in the centre of the image. I'll check the corners this evening. Good link, BTW.

Thanks

Peter

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Answer 5

Ian Wood

Level 5

4,350 points

Jul 11, 2007 7:30 AM in response to Rusty Rat

When I checked for CA (actually TCA) I was looking
more in the centre of the image. I'll check the
corners this evening.

CA is, by definition, non-existent in the middle of the image because the lens isn't bending the light much. Definitely compare the extreme corners of an images to see it's effects.

AFAIK, Aperture does no CA correction at all, automatic or not.

Ian

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Answer 6

Rusty Rat Author

Level 1

6 points

Jul 11, 2007 7:47 AM in response to Ian Wood

Yes, the article made that clear -- the centre would be OK but the corners would have problems. Something I used to know, but forgot.

I'll check the corners of a few images for CA this evening.

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Answer 7

Rusty Rat Author

Level 1

6 points

Jul 11, 2007 3:21 PM in response to Rusty Rat

Yup, it's TCA in the lens -- the centre of the images are fine, but there's purple fringing on the high contrast edges in the corners.

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