Is this chromatic aberration?

codrus

Looking at some pictures I took over the weekend, I noticed purple edges to the highlights in some of them. Is this chromatic aberration? I see them in this shot, particularly around the edge of the mirrors:

http://codrus.smugmug.com/gallery/6566164_6yd4E#417936212_zskT

Whereas this shot from a similar angle doesn't show them:

http://codrus.smugmug.com/gallery/6566164_6yd4E#417940508_RN4zP

Both are shot with my 50D, the first with the Canon 50mm f/1.8 II and the second with the EF-S 17-55 f/2.8. Is this just the $80 vs $1K lens price showing through, or is it related to the difference in aperture (both are wide open)?

thanks
--Ian

LiquidAir

Purple fringing is not the same as chromatic aberration, but it is a lens artifact. You were shooting at f/1.8 with the 50 which not going to give you the best quality that lens can deliver. If you are looking for sharpness, try stopping down to f/5.6.

pyry

LiquidAir wrote:

Purple fringing is not the same as chromatic aberration, but it is a lens artifact. You were shooting at f/1.8 with the 50 which not going to give you the best quality that lens can deliver. If you are looking for sharpness, try stopping down to f/5.6.

Depends on what you mean by purple fringing, I think it's usually the lateral kind of chromatic aberration. However, in the particular shot mentioned above with the 50mm, the mirror is surrounded by flare.

In the same shot: take a look at the reflections of the sky on the side of the car. Behind the mirror they are fringed green, and further forward in purple. This is longitudinal CA - the colour of the fringe depends on the highlight being forward or behind the plane of focus.

This is what lateral CA looks like. The fringes either favour one side (or seem to, because the other side is too bright to show it) of a strong contrast or change colour from one side to the other.

And yes, the 17-55 is less prone to any of this than the 50mm.

Tee Why

It looks like CA to me as well.
The lens doesn't have that much but per slrgear's test, looks like there is a bit less of it when you stop down by f4.
Here is a link to the test.
http://www.slrgear.com/reviews/showproduct.php/product/150/cat/all

DPP and LR both have ways to reduce it as well in post processing.

codrus

Thanks folks. I hadn't actually noticed the green fringing in the background before, interesting. I don't really want to stop down and lose the blurred background.

As for postprocessing, I'm using Aperture. Any idea if there's a way to reduce it in there? I haven't seen it mentioned in what I've gone through on it so far (only started using it about a month ago).

thanks,
--Ian