chromatic aberration

I have just been hunting my local churchyard for lichen this pm with my 50mm 1.4., eagerly downloaded to develop my raws and was intially well pleased with results, however when going closer in as you can see from detail I have cropped for illustration there is a halo effect on top left, is this what you call CA that I have heard about but not actually noticed in my images myself?
Is it present in ALL lenses?
Is it more evident in wide open apertures?
Is there not a lot one can do about it?



1/250s @ f2.8 100iso 50mm

cropped detail:




Lilly

Chromatic abberation shows up typically as purple fringing and is a reult of the three colours of light not all focusing in exactly the same spot. There are also effects from oblique light at the edge of the CCD causing light spillage and diffraction effects that amount to the same thing.

Digital lenses should be better in this respect, and many of them are. Likewise, APO (apochromatic) lenses are corrected for all light colours, not just two as in an achromatic lens. Of course there are degrees of how well these vcorrections are made, and some cheaper APO lenses may not be particularly good.

The effect you have here, which is quite difficult to see on my monitor, seems to be more of a halo and it looks like a sharpening artefact. It is really difficult to be sure without being able to examine the file properly.

Did you sharpen this a little too much. Some RAW converters automatically sharpen by default and if you have sharpened as well it may have been too much.

CA is present to some degree in many lenses, especially older ones designed for film. It can be corrected for in software. It is worse in high contrast areas, such as branches against the sky.

Hope that helps!

Not sure about chromatic abberation, that first sentence is definetely a grammatic abberation.

I can't see anything other than a slight loss of sharpness in the fine detail. When did you last clean your monitor? Does the affect show up in print?

Was the lens clean? In this weather, moving back and forth between cold and warm environments can put a thin film of condensation on the lens which would affect sharpness.

Difficult to say if that really is CA. What does the lower right corner look like? Round the little whiteish speck you should see the same (CA is worse in the corners than in the center) if it really is CA.
I would also think that what I see in your crop is not CA but some other halo effect. I haven't got a clue, though, what it might be. CA should be less broad, for a fixed focal length lens only a few pixels.
(It's easier to correct fixed focal length lenses for CA than zooms and the longer the lens the easier it should get. My "worst" lens in respect to CA is the 10-17 fisheye, i.e. very wide angle and zoom. However, SilkyPix does a pretty good job in correcting CA.)

Prieni

One of the clearest explanations of CA I've come across is at:

http://www.vanwalree.com/optics/chromatic.html

I'd never understood the difference between axial and transverse CA before, nor why CA sometimes manifests as fringing, and at others as separated colour bands.

Looks either slightly out of focus, or it might be motion blur. Were you using a tripod? If you did, was SR on or off?

Well, I sharpened only in CS2 at end of PP and only at 100%, I was using a monopod with SR on, def. not motion blur.
Preini, here is the detail of the white spot you mentioned, just seems to be a little cyan fringing, but not as bad as previous detail or maybe you will disagree?



I agree it does seem to be more of a halo effect, perhaps because of the light background contrasting sharply with the stone.
So, maybe it is not CA but just a mix of circumstances when I took the shot.
I was just curious to see if any of you could immediately recognise this annoying imperfection and whether I could avoid it in the future.

thanks Lilly

Lilly,
I can't see the latest detail. But from your description it seems that what you see in that latter detail is chromatic abberation, so the effect in the upper right corner must be something else...

Prieni

Sorry about that, moment of madness, I must have emptied the files out of the Bucket!

I have since been researching this further and John may be correct in suggesting this may be the problem, I quote Scott Kelby re: sharpening

" the more you use it, the more discerning you'll become about it (you basically becoming a sharpening snob), and at some point, you'll apply some heavy sharpening to an image and notice little color halos. you'll grow to hate these halos, and you'll go out of your way to avoid them. In fact, you'll go as far as to use this next sharpening technique, which is fairly popular with pros shooting digital (at least with the sharpening-snob crowd)".........Luminosity Sharpening..............

guess what I shall be doing this evening!
Lilly

Lilly,

Mattmatic has some great sharpening tutorials on his website