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Old Mar 3, 2006, 1:19 PM   #1
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Well I was doing some close up shots of some flowers, and as you can see in the upper right, what would be the best way to reduce on the CA that is present? Given it was windy as ever, and i had to wait almost a minute for the flower to remain still, I dont think it is motion blur. Any suggestions? Thanks!

John
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Old Mar 3, 2006, 1:49 PM   #2
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imo; looks like 'purple fringing', not CA
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Old Mar 3, 2006, 2:56 PM   #3
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Unless you were trying for a depth of field that shallow, you could see if stopping down the aperture a bit might help (sometimes it does).

You were shooting with the aperture wide open at f/2.7. So, using Av (Aperture Priority Mode) and selecting a smaller aperture (higher f/stop number) may help a little bit with some models (and you'd have more depth of field that way, too).

Also, your lens has more distortion at it's widest setting (and you were at it's widest zoom setting for this shot). That can also impact fringing to some degree.

Steve noted in his review of your model that it did tend to have some fringing at high contrast areas with highlights throughout it's focal and aperture range. However, he noted the S1 IS fringing improved as focal lengths got longer.

I don't know if you can zoom in any in Macro mode or not with your camera and shoot from further away. If so, I'd give it a try so that you've got less distortion from the lens.

But, virtually any digital camera can get a bit of fringing in high contrast areas, particularly if they're overexposed any. Dialing back the exposure brightness may help some, too (using a -EV setting with exposure compensation then brightening up the image later in software).

I've seen many theories on what causes this problem (ccd blooming where electrons spill over into adjacent photosites, lens aberrations, coatings, etc.).

Lens design/quality/distortion can impact it, as well as things like the microlens design in the sensor. Each photosite has a small pillow shaped microlens over it, which can cause light to defract in a way as to cause fringing, according to a Senior Kodak engineer who commented on it a few years back (and that's only one cause).

I wouldn't worry about it too much, as it's barely noticeable at all to an untrained eye, and you can correct fringing using software tools, too.

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Old Mar 3, 2006, 3:02 PM   #4
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P.S.

Of course, the best way to avoid it is not to take photos with that much contrast (white against black with strong differences in brightness, etc.). :-)

But, that may not always be practical. So, you either try to reduce it via technique/camera settings, or correct it later if it becomes objectionable at the viewing/print sizes needed.

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Old Mar 3, 2006, 3:07 PM   #5
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I do know that I was using the super macro mode, which has a focusing distance of even 0cm. I had tried getting some shots with a longer focal length, but as noted before, without holding the flowers in some way, it was about near impossible to get them to stay still. Yea, I was also trying for shallow DOF, and also just trying to get some really good shots with lots of detail.

I am also looking at the Canon 500D close up lens for maybe more assistance when doing shots like these. As the super macro mode, you cannot zoom at all, it stays at the shortest focal length of 6mm (36mm equiv). But I will try stopping down the aperature a little, see if it helps, as I was able to have 1/1200 shutter speed.

Thanks for both of your suggestions and comments.

John
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Old Mar 11, 2006, 5:58 PM   #6
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If you shoot RAW, some raw processors have built-in CA correction functions (Silkypix is one).

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Old Mar 21, 2006, 12:30 PM   #7
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In this instance, it looks like real chromatic aberration rather than imager-based blooming to me. I only notice it in the upper right corner but not around the other edges of the flower. If it is only occasionally objectionable, I would correct the problem in software. In this instance, the background is almost black. Thus I would take a color sample from a nearby point on the flower and paint over the edge in "color" mode. This will change the hue and color saturation of the edge to resemble the nearby flower without altering the brightness.
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