Chromatic aberration: what it looks like and how to fix it

[gardener]

My embarrassing (and by now ridiculously expensive) search for a good quality compact to replace my much-loved Finepix f31 continues as I wasn't happy with the P6000. Lots of mushy pixels and un-needed bells and whistles but a serious lack of ability to focus on low contrast subjects. The camera is needed to photograph plants and lichen, often in less than ideal conditions.

In despair and desperation I've forked out for the Lumix LX3 and like it much better but I'm getting bright blue fringing on quite a few images - is this what's known as chromatic aberration and if so is there anything I can do about it? (Other than take up knitting again!!! )



Jenny

[Henry Peach]

Some software has CA fixes built in. In Photoshop I deal with it in Camera Raw. you might try googling "fixing chromatic aberration" along with whatever graphics software you are using for lot's of tutorials.

[McQ]

Hi Jenny. That certainly looks like subtle chromatic aberration (CA) to me. CA generally has either a cyan or magenta hue, and increases in size radially outwards from the center of your image. CA is also most pronounced near the border between light and dark subject matter. In your case, the contrast between the lichen and tree trunk is what brought out the CA. However, this contrast is subtle compared to dark branches on a bright sky, for example, which would likely exaggerate the visibility of your chromatic aberration dramatically. Just something to be aware of...

In addition to the CA removal feature in Photoshop's Camera RAW, using a smaller camera aperture can substantially reduce CA if you were previously shooting wide open.

[Colin Southern]

Hi Jenny,

Long time / no hear!

Not sure what to suggest with this - CA can be a way of life with this type of camera. All I can think of is using post-processing to try and reduce it.

Adobe Camera RAW when used with photoshop has a CA reduction tool - best used on RAW images, but it's a pretty expensive solution and still won't get things 100%.

You might have to either go back to knitting or do away with the desire for a compact camera and go the SLR / quality lens way

[txfred]

The optics of a modern camera lens should be free of serious chromatic abberation. Have you contacted the manufacturer? I am in the process of converting from film to digital. The thing I suggest is experimentation. Set up the camera with fixed lighting and methodically record images with changes in settings: ISO, sharpness, etc. There is no way an individual could do a marginal study of a single camera...

[Dave Humphries]

Hi Jenny,

McQ's description of how CA typically exhibits itself is accurate (of course), but I'm not sure what I see fits this unless this was quite a small crop off the edge of a much larger image. It's all a bit (well a lot) one sided for a full image.

Although it's difficult to imagine how such an effect might have arisen otherwise, a faulty camera is one possibility.
Is the full size original available for a better diagnosis?

Regards,

[cav]

I agree.
The image looks like it has CA.
If this is the whole image then the lens is faulty or mis-aligned.
If this is a crop and enlargement then it is difficult to quantify.

The amount of distortion can be reduced by reducing the aperture of a lens.

[gardener]

Thanks for all the replies, and yes it is a very hard crop taken from one corner

Is the full size original available for a better diagnosis?

Below is the original untouched photo but I had to downsize seriously to post. The bit with the CA is bottom centre. Viewed at print size rather than actual pixel size (first image posted) its not really noticeable but its not something I've suffered from before!

[McQ]

Yes, if you look at the top right of the photo, there's even more pronounced red/magenta chromatic aberration near the border with the bright sky. Makes more sense seeing the full photo.

Looking a bit deeper though, I see that you took this shot at f/5.6. Since the Panasonic Lumix LX3 has a range of f/2.0-f/8.0, I don't think I would recommend using a smaller aperture in this case since you will begin to lose resolution due to diffraction. However, I also noticed that you took the shot at a focal length of 5 mm (24 mm equivalent on a 35 mm full frame camera). That is the widest that the Limix LX3 lens can go. At such a wide angle on a zoom lens, you very well might be noticing more CA than you would at similar apertures elsewhere in the zoom range. For a macro type shot such as this one, I don't think it would hurt to compress the perspective a bit and zoom out a little (with the same framing). Just something else to try...

[gardener]

Ah, so does that make it more likely that the problem is me and how I'm using the camera rather than a fault with the camera itself?

[McQ]

The camera is certainly the cause, but all cameras/lenses exhibit some CA -- no matter how high-end a model that camera might be. To be honest, the amount of CA exhibited in your shot really isn't that bad in the scheme of things. If you had tried taking the photo at f/2.0, you'd likely notice that the CA would be several times wider, for example. I think you'll be surprised how effectively CA can be removed in post-processing, as mentioned using Adobe Camera RAW, etc.

That being said, there are definitely cameras out there that do not exhibit as much CA as in your example, but those cameras likely don't share all of the advantages of your model. Size, weight and price are a few that come to mind. Photography equipment is all about trade-offs -- there's no perfect lens or camera for all subjects/conditions...

[William W]

I also noticed that you took the shot at a focal length of 5 mm (24 mm equivalent on a 35 mm full frame camera). That is the widest that the Lumix LX3 lens can go. At such a wide angle on a zoom lens, you very well might be noticing more CA than you would at similar apertures elsewhere in the zoom range. For a macro type shot such as this one, I don't think it would hurt to compress the perspective a bit and zoom out a little (with the same framing). Just something else to try...

I have not looked at the image closely, but have read all the text. IMO this nails the main contributing factor and will be the easiest fix, without changing cameras.

I also agree not to stop the lens down any further.

WW

[William W]

That being said, there are definitely cameras out there that do not exhibit as much CA as in your example, but those cameras likely don't share all of the advantages of your model. Size, weight and price are a few that come to mind. Photography equipment is all about trade-offs -- there's no perfect lens or camera for all subjects/conditions...

Agree, again.

I am hustling to find a beautiful image of a modern, feature-window with steel supports, in a newly renovated City Hotel. I captured it last December with my EF24/F1.4L on a 5D.

The un-retouched image exhibits fantastic CA especially at the edges - worst the corners.

Ah, cannot find it - trust me, the CA is there even with the "L" expense.

WW

[Bill44]

CA is a known problem more or less dependent on the camera and lens. Nikon acknowledge the problem to the extent that they have built CA correction into the D90.

[Dave Humphries]

Hi Jenny,

Thanks for posting the bigger picture, it certainly proves the culprit is CA.

I can't really add anything useful to McQ and WilliamW's advice; i.e. step back a little more from the lichen and zoom in a bit to get the same size framing you have here. Don't overdo it though, or in the dim conditions, with the longer focal length and shutter speed, camera shake may become an issue. I'm guessing that's why you went in close to start with.

Beyond that, you could try some CA correction in PP, which I would imagine is best applied to the whole image before the cropping is done - but I've never done it, so I could be wrong there.

Hope that helps,

[Colin Southern]

Hi Jenny,

I'd be interested to see how much it could be reduced in post-processing. Be happy to run the full-res file through CS3 for you if it helps?

[cav]

Now we can see the whole picture, I can't really add anything useful to McQ and WilliamW's advice either.

[gardener]

Thanks for all the replies - I tried moving back and zooming a little (now that gives a daft mental image ) and that has definitely helped.
I've only got Adobe CS and a PC that can't cope too well with big file sizes so for the moment I'll probably have to give Raw a miss and concentrate on overcoming camera shake and improving focus.

Thanks for the offer of running it through CS3 Colin, but as I can't afford to get a copy myself it would be a bit of a wind-up at the moment to see what could be done if I only had the money!