70-200 f/2.8L purple fringing

[alex.krebiehl]

Just got my EF 70-200mm f/2.8 today and was doing some test shots outside. This is a crop of some tree branches against the sky. Is this much purple fringing normal?/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.36.66/IMG_5F00_2630-crop.jpg

[wickerprints]

Gaaahhhhh....





That's awful. But you do not say what distance the lens was focused, what aperture you used, and what the lens looks like in the center and in each of the four corners.


If the lens is not focused on the branches, then you will see some axial chromatic aberration wide open, yes. But even this seems excessive.

[alex.krebiehl]

Here is the origional with the cropped section circled (crudely).





Canon 50D 70mm f/2.8 1/200 ISO400 focus distance was roughly 30 feet. idk it was just a random shot at tree branches





/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.36.66/IMG_5F00_2630-full.jpg

[asmodai]

My 70-200 2.8 normally performs extremely well. But ONE TIME, I got some nasty fringing, shooting something a lot like that (overcast, bright, with plant life in front of it. It reduces pretty well with anti-fringing tools.





In the future, just stop down a bit more. It may sound hollow, but if you think about it, you're only going to get these against an overcast bright sky. You'll have the light to stop down, and since the background is a sky, you probably won't notice the larger DOF. Anyway, stopping down just a little should be sufficient.

[Fast Glass]

Over-cast backround with the skyvery brightis one of the worst things you can put a lens through in terms of showing CA.


John.

[Jon Ruyle]

I don't claim to know exactly how much is too much, but John and wikerprints are right- ca is worst wide open and worst in high contrast situations like the one you have here.


On the 70-200mm, CA is also worst at 70mm, according to this photozone review ("http://www.photozone.de/canon-eos/199-canon-ef-70-200mm-f28-usm-l-is-test-report--review?start=1). They describe the lateral ca of the 70-200 IS as "relatively pronounced", though according to them, it should be about one pixel on an 8mp rebel (which is still less than 2 pixels on a 50d). Your picture seems to have more than 2 pixels of purple, but then, you are shooting a bright white background which is tough. If the background is overexposed, one can get even more purple. (I didn't see where the photozone guys state under exactly what conditions they tested 1 pixel of CA)


Again, I don't claim to be able to judge how much CA is too much. But your results- given that you've combined a number of factors to make CA as bad as possible in a lens that does not particularly control CA well- do not surprise me.


I should mention that I do not mean to bash the lens by referencing a review which says it does not control CA well. I own and love the 70-200 f/2.8 IS- it is in fact my favorite lens.

[Fred Doane]

Alex,

Some of the purple fringing can be corrected in Photoshop if you are shooting in RAW format. I'm sure other software can do the same. it may not eliminate all of it but it might be able to correct for some of it. I have the 70-200 L 2.8 (non IS) and love it. I would say like everyone else that the pic you posted is an extreme circumstance. I shoot that lens primarily at 2.8 and have not come across the CA issue as bad as that ever. If you have the RAW image still try processing it using the tools in photoshop and see what you can come up with and post the results for everyone to see.

Fred~

[alex.krebiehl]

If there is an easier (or more effective anyway) way to remove fringing, please let me know. I just loaded it up in Photoshop, selected the Hue/Saturation adjustment on the blue channel, sampled the fringing, then dropped the saturation to -90. Here is the after-adjustment photo and the crop.


/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.36.66/after.jpg





/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.36.66/after-crop.jpg

[DavidEccleston]

If there is an easier (or more effective anyway) way to remove fringing, please let me know.


Not sure how the quality compares, but there is an easier way, if you shot RAW. Open pic in DPP. Go to NR/Lens/ALO tab. At the bottom there is a "Lens aberration correction" section, with a "tune" button. Click that. Check the box for "Chromatic aberration".


If you did shoot RAW, try it and let us know how the results look.