Chromatic Aberration with the Tokina 10-17mm??

Hi boys and girls, I need a little help here.

I'm playing in the pool with my new Sea & Sea MDX40D with the Canon 40D, trying out lens and port combinations. Basically just getting a feel for what the system will do. I loaded up the Tokina 10-17mm and the NX fisheye dome port with no extension. I don't have a nice color chart like Stephen so I put a chipping net (who has time for golf anyway) in the pool thinking I'd use the strands of rope to learn something about DOF. The first image was shot at F/8.0 1/160 sec. strobes at 1/10 power. A bright sunny day in the desert. ISO 200 with the lens @ 10mm. Afternoon sun from the left of frame. No changes from as shot. There is some blue fringing showing up around the white letters. The second image is a 200% crop from the lower left in camera RAW then sized in CS3.

So my questions are; Is this a text book example of chromatic aberration (CA)? Is this normal in big domes? Is it due to the lens being to far forward in the port or .....?

Clearly the black with white lettering is a high contrast worst case scenario. In real life will this show up? I keep thinking about blue fringed Manta silhouettes.

The next question is, what can I do with technique to lessen the effect? The third image is a 200% crop from a different shot, F/22 1/200 sec with the lens at 17mm. Most of the light coming from the strobes @ 1/4 power. Strobes were positioned about 1/2 m to each side, angled out slightly. I noticed less CA and that it's lower on the letters. Do you think this is due to the light coming from the strobes instead of the sun or is it due to the lens being zoomed to 17mm?

If I'm stuck with the CA just due to my port/lens setup, is there anything I can do about it in post processing? Is there a really good question I'm too dumb to ask?

Really appreciate any thoughts,

Steve

Steve,

I believe this purple fringing is a "feature" of the lens (and other fisheye lenses) that occurs in high-contrast areas.. you won't see this in every shot, just ones with very high-contrast transition points.

Its not your port/lens setup.

These purple fringes are usually harder to remove in photoshop than standard lateral chromatic abberations.

I haven't had luck removing ones from this lens in CS2 but maybe others have...

maybe others will also chime in with their thoughts.

hope this helps

Scott

I find it's not that bad but you will get it topside as well with some high contrast areas.

If you have CS3, the CA corrections in the RAW converter can take some of it out...

edit: and Steve, can't you get some pretty U. of Arizona students to pose for you in the pool instead of the chipping net?

Steve, can't you get some pretty U. of Arizona students to pose for you in the pool instead of the chipping net?

Thanks guys I'm feeling better. Yeah Mike, my son goes to the Uof A so we are contantly having the young ladies over. The problem is it's so warm in AZ ... they don't wear suits, so I can't post them.

Steve

If you have CS3, the CA corrections in the RAW converter can take some of it out

Steve

There are two types of CA, lateral and axial (or longitudinal). The CA sliders in ACR, Lightroom etc, are used for removing lateral CA. Purple fringing is the result of axial CA and the controls for removing lateral CA may not always be effective.

Here's a photoshop technique for removing purple fringing:

http://www.great-landscape-photography.com...e-fringing.html

There are two types of CA, lateral and axial (or longitudinal). The CA sliders in ACR, Lightroom etc, are used for removing lateral CA. Purple fringing is the result of axial CA and the controls for removing lateral CA may not always be effective.

 

Here's a photoshop technique for removing purple fringing:

 

http://www.great-landscape-photography.com...e-fringing.html

Steve

gudge, thanks for the link, I haven't had luck with the CA sliders in ADR on the purple fringing, it seem to change it, but not improve it.

scott

Fringing is often a "localised" problem within an image, often affecting and most obvious in monochrome areas. If the ACR tools don't fix it, I do the following which is quick and simple.

Open the image

Make 2 Duplicate layers (so you have 3 altogether)

Turn off the visibility of the top layer

Select the middle layer

Bring up Adjustments>hue/saturation palette and reduce saturation of either magenta or blue or both until the fringing in the affected area looses its colour.

Select and make visible the top layer

With a soft-edged eraser, erase the top layer in the area of the fringing.

Flatten and Save.

Done.

I haven't had any experience trying to correct CA, but I did stumble across this link several months ago and seems to be appropriate to the conversation.

http://www.camerasunderwater.info/optics/lenscorrect.html

Cheers