17-40L Purple Fringing

[TWM]

Well I just took my new 20D and my 17-40 F4 L out this afternoon and took a lot of photos. I surely was disappointed. I know that I have to practice and a lot of the poor results, I think I know how to work on. The one that bothers me the most is that there is purple fringing (I think that's the term) on a lot of the tree branches that are taken with the sky behind. I wouldn't think that should be a problem with this "L" lense. Attached is one of the photos and another of only the branches. Please advise

Thanks Tom:)

[fetching]

why is that top photo so pixelated?

[Cadwell]

The sky looks over exposed. Just as likely to be sensor "blooming" than CA and quite possibly not a lens problem at all. Retry the shot with exposure correct for the sky and see what you get.

[lancea]

I noticed the same thing on my first "day out" with my lens when I took some shots of a ridge. On my PC, when I zoomed-in on the trees that were against the sky at the upper edge of the shot I saw purple fringing too. It has appeared in similar situations where the edge of a building is against the sky, so perhaps just an extreme situation.

[Redbird_xo]

Stopping down to a smaller aperture might help to reduce CA to certain extent. Of course, digital sensor is bound to have some degree of CA problem.

[griff2]

I noticed this fringing with my 17-40, however I don't think its that bad - compared to the kit 18-55, for instance.

[Tom W]

Any lens can be coaxed into either CA or purple fringing if the exposure is very high for that part of the image, and the contrast is very high between the adjacent surfaces. As suggested, expose for the sky and see what the fringing looks like.

The 17-40 is generally a very clean performer.

BTW, the top image appears to have been oversharpened quite a bit.

[TWM]

Thanks for the input. I'll reshoot and set what happens. Neither photo was sharpened at all. It was taken raw and then processed for exposure, brightness etc. but no sharpening. It's an 8 MP raw picture converted into a 96k jpeg.

Tom

[Tom W]

It was probably the conversion process that did it. Convert to a higher-quality (medium-high to high) and save it that way. Then open it and resize it to a useable pixel size such as 750X500. The software really mashes things up when it reduces that drastically.

[TWM]

I sent this before but it got lost. If it turns up again,forgive me. After all the recent talk about the 70-300 DO IS, I ordered one from BuyDig this morning.
I know some people say it isn't sharp enough at 300mm but I generlly can't tell the difference between different lenses. I like the photos that have been posted here with that lens so I think I will be happy with it. Iwas going to buy the 70-200 F/4L, But I decided it was too long and too white. Now I suppose I should sell my 28-135 IS. I bought a 20D, 4 lens, tripod and 580ex about a month ago before I knew what I needed or wanted ( same thing I guess)
I'm glad that I pay the bills or my wife would know what these things cost. D I V O R C E.

Tom M:lol: