[Rosegold]

Hi all,

I noticed something on a shot of a blackbird I took the other day, is it chromatic abberation? And if yes, what is that and how do you avoid it?

It's a discoloured area in the grass, bottom left. I've saved the un-edited file as a jpg and re-sized and set to 72ppi to upload here.

It was overcast off an on, but I thought it was bright enough. I was using my Sigma APO 80-400mm F4.5-5.6 EX DG and not thinking beyond getting a decent shot before my arm dropped off!

Exif Info

Capture Date: 2007-05-09 15:17:34
Exposure Mode: P - Program AE
Exposure Compensation: 0
ISO Setting: 100
White Balance Setting: Auto
Flash: Off
Shutter Speed: 1/125s
Aperture Value: F5.6
Metering Mode: 8 Segment Metering
Focus Setting: AF-S - Single Auto Mode
Focal Length: 400 mm (80-400)
Resolution: High
Drive Mode: Continuous Shooting
Camera: SIGMA SD14 01002406
Firmware version: SD14 1.02
Image Unique ID: 30313030323430360EE64146560BB00B
Saved X3F Settings
Exposure: +0.0
Contrast: +0.0
Shadow: +0.0
Highlight: +0.0
Saturation: +0.0
Sharpness: +0.0
X3F Fill Light: +0.0
Color Adjustment: 0

Thanks

[Dabhand16]

Chromatic abberation is found in high contrast areas like where the edges of buildings, trees etc have edges that meet the sky. The outlines will have a blue/violet fringe that is usually an indication of poor lens quality or coating, but the effect varies depending on the individual conditions and angles of the light.

The discoloured area in your image is most certainly not CA. If this discolouration does not appear in any of your other shots, you can rule out anything to do with the camera, and it is most likely brown grass that you did not notice at the time you took the shot.

Looking at it closely, or as closely as my old eyes will allow, the brown area does appear to have a shape, but it seems there are white-ish areas on either side, so perhaps it is just a quirk of that shot.

I guess this picture was taken in the same place as the other one in the gallery, but just a little to the LHS of that one, and there is no discolouration in that shot, so I would not let it worry you.

[Rosegold]

Thanks for the info and comments Dabhand, I was a bit worried about it as the bird seems to be looking at it and it's a bit distracting, maybe it's a sprite I really like this shot otherwise, so cropped it to upload to my personal gallery.

[Markulous]

Here's an example of CA - not too bad here but visible as a green offset tinge to the left and red to the right. My kit lens - usually found @ max focal length and at the edges, especially corners


Your shot looks more like lens flare, or a flare artefact (maybe something reflective just out of shot?). I suppose it's possible that it's caused by an optical fault in the lens (light bouncing inside lens off a glass fault) but I'd have to say extremely unlikely. Worth checking a couple of other shots - same focal length (400mm) and aperture (F5.6). There again, it may be sprites........ or, more likely, pixies!

[Soupdragon]

The other alternative would be an insect or the likes flew through the optical path fairly close to you.
Because anything that close would be completely out of focus and you are not seeing this on other shots, my money is on the ignorant bug!

[Soupdragon]

Another possibility would be that the black bird has also spotted the brown anomaly and is too investigating it.

[Markulous]

Ahh, good thinking, Soupy! Foreign object between (even on the lens) much more likely! Your money is safe, I reckon!

[Rosegold]

Thanks guys, I now know what to look for if I'm worried about Chromatic Abberation. Mark the visual example was helpful. I don't think the lens is at fault as I've taken loads of shots at 400 and it's not come up before, so I'm going with either the lens flare/artifact theory or the pixies *lol* I had something similar happen with my 12-24mm I think when phaffing about taking shots of my street, but I've deleted them now so can't check. I appreciate the help!

[Hacker]

Are you sure a dog hasn't pee'd on your grass?

[Rosegold]

Well, with Murphy anything is possible!

[Dabhand16]

Originally Posted by Rosegold

Well, with Murphy anything is possible!

Yes, but what about the dog?

[orangepeel]

Originally Posted by Dabhand16

Chromatic abberation is found in high contrast areas like where the edges of buildings, trees etc have edges that meet the sky. The outlines will have a blue/violet fringe that is usually an indication of poor lens quality or coating, but the effect varies depending on the individual conditions and angles of the light.

that's not actually quite right. the thing you're describing is purple fringing. Visible in high contrast areas as you say but is actually caused by light overflowing from one sensor pit to adjacent ones. In this case it's the body and not the lens that has the issue. Although you are right in that different conditions can effect it in different ways.

CA is caused by lenses not focussing the different wavelengths of light to the same plane.

You can correct CA quite easilly but with purple fringing the original data is lost so the best you can do is desaturate" the purpleness.