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Old Sep 9, 2009, 9:16 AM   #1
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Default Purple Fringing with 85/1.8D on D90

I'm using a Nikon D90 with an 85mm f/1.8D to shoot indoor equestrian action. The images all have areas of high contrast (black saddle, white saddle pad, black boots, chrome stirrups, etc.) and I'm getting a lot of purple fringing.

The 85mm f/1.8D is the only lens I've got so far, so I don't have anything to compare it too. It seems to happen at both f/1.8 and at f/2.0. (Stopping down much further defeats the purpose of having a large aperture lens.)

I used Auto WB (at f/1.8) and a Preset WB (at f/2.0), and the results seem to be slightly better with the Preset (at f/2.0), but the lighting varies (mercury vapor + sunlight) so the images have a variety of color casts depending on the location of the subject within the arena. Naturally, the PF happens in sunlight, not under the mercury vapor lights.

Attached is a 100% crop.

The results are several orders of magnitude better than I've gotten with my KM5D and Minolta 135/2.8 or Sigma 90/2.8 Macro, but I was hoping for less PF.

Any ideas?
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Old Sep 9, 2009, 9:30 AM   #2
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So, did you buy a D90? How do you like it so far?

The D300 has automatic correction of CA built in. It seems to work quite well. Although it's not listed as a feature, users seem to think the D90 has CA Correction, too (which makes your results puzzling).

Some of that could be blooming, too. The white behind the riders boot is overexposed (most of that section is showing up as "blown" when I look at it with an editor, yet I see no blocked shadows). So, the overexposure may be contributing to the problem. You may want to try dialing in a bit of negative exposure compensation so that you're exposing a bit darker and see if that helps the problem. If you're using any filters, I'd remove them (as that could be causing a bit of optical degradation).
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Old Sep 9, 2009, 9:52 AM   #3
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More suggestions:

You said your son has a D300, right? You may want to try that lens with both cameras and see if the D300 corrects it automatically for you, and if so, consider returning the D90 for a D300 instead (although I have seen D90 users claim it's got CA correction, I'd try it yourself to find out, since Nikon does not show that feature for the D90)

You may also want to try shooting in raw and using Capture NX 2 to process the images and see if it can automatically correct it for you.
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Old Sep 9, 2009, 10:59 AM   #4
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The D90 does correct CA, same as the D300. But only with JPegs. It cannot be turned on - or off. Shooting NEFs will require VeiwNX (release 1.4.1) or Capture NX to take this out of the raw files.

This looks at LOT worse than the worse case I have ever seen from my 16-18 3.5-5.6 VR.

Garry
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Old Sep 9, 2009, 11:04 AM   #5
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That's what I've seen some users claim (the D90 also corrects for it). But, you wouldn't know it by looking at that image. ;-)
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Old Sep 9, 2009, 11:12 AM   #6
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Quote:
Originally Posted by JimC View Post
More suggestions:

You said your son has a D300, right? You may want to try that lens with both cameras and see if the D300 corrects it automatically for you, and if so, consider returning the D90 for a D300 instead (although I have seen D90 users claim it's got CA correction, I'd try it yourself to find out, since Nikon does not show that feature for the D90)

You may also want to try shooting in raw and using Capture NX 2 to process the images and see if it can automatically correct it for you.
I was under the impression the D90 does have lateral CA correction but have found conflicting opinions to the actual truth. I do know the D300 and D5k have it, so I would assume the D90 does too. Shooting in RAW, whether or not the correction is applied may depend on your method of conversion. I know nikon's software gives you the option to remove it if you want. When shooting jpeg, the correction should already be cooked in.

On a side note, although i don't have the 85 f1.4, I've noticed considerable CA issues with older (non AFS lenses). My 50 f1.8 shows pretty bad CA under certain situations. With newer lenses, it's not as bad an issue, and my d300 does a good job of eliminating CA. I haven't shot my d5k enough to make a call on how well it does at correcting the flaw.

Also, TC, welcom to the dark side
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Old Sep 9, 2009, 11:53 AM   #7
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I saw a thread not long ago on another forum debating it. Apparently, a D90 user got a response from Nikon that said the D90 did not have it. Yet, other users insisted it did (saying that they saw CA in raw images that were not present in jpeg images when using a specific raw converter (but, I don't recall all of the details about it).

That's why I'd try it with both cameras in the same conditions and compare the output to find out for myself (especially given the amount of PF in that D90 image).

The closest thing to PF I've seen from a D300 is this photo in Steve's D300 review samples (taken with the 18-200mm VR lens). Note the faint outline around the bird's head. Dial up warning (this is a link to a full size original):

http://www.steves-digicams.com/2008_...s/dsc_6855.jpg
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Old Sep 9, 2009, 2:30 PM   #8
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Quote:
Originally Posted by JimC View Post
So, did you buy a D90? How do you like it so far?
It is very nice. I'm getting used to the position of the ON/OFF switch, and I miss the LCD display turning off automatically when I put my eye to the eyepiece, but otherwise it's a big improvement over what I'd been using. (Duh!)

Quote:
Originally Posted by JimC View Post
The D300 has automatic correction of CA built in. It seems to work quite well. Although it's not listed as a feature, users seem to think the D90 has CA Correction, too (which makes your results puzzling).
I can't find anything that confirms or denies the feature in the D90 or the D300 for that matter.

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Originally Posted by JimC View Post
Some of that could be blooming, too. The white behind the riders boot is overexposed (most of that section is showing up as "blown" when I look at it with an editor, yet I see no blocked shadows). So, the overexposure may be contributing to the problem. You may want to try dialing in a bit of negative exposure compensation so that you're exposing a bit darker and see if that helps the problem. If you're using any filters, I'd remove them (as that could be causing a bit of optical degradation).
Blooming is something I hadn't thought of. That saddle pad sure is WHITE!

That 700x525 crop is is a small part of the 4288x2848 image, which looks spectacular, and I'm definately picking nits, but I was a little disappointed when I first saw it at f/1.8. I'm handling one problem (?) at a time, and this one seems to have escaped my efforts thus far.
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Old Sep 9, 2009, 2:39 PM   #9
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I'd expose a stop darker and see if that helps (since none of the darker areas were underexposed enough to lose any detail in that crop, yet the white areas were overexposed). I see where you were using Center Weighted Metering, which is probably going to be more consistent. So, I'd try dialing in -1 EV with Exposure Compensation (which would have the added benefit of faster shutter speeds for a given ISO speed/aperture/lighting) and see what you get. Then tweak from there.
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Old Sep 9, 2009, 2:43 PM   #10
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Quote:
Originally Posted by JimC View Post
More suggestions:

You said your son has a D300, right? You may want to try that lens with both cameras and see if the D300 corrects it automatically for you, and if so, consider returning the D90 for a D300 instead (although I have seen D90 users claim it's got CA correction, I'd try it yourself to find out, since Nikon does not show that feature for the D90)
The D300 costs twice what I paid for the D90. For that much money, I'll put up with a little PF.

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You may also want to try shooting in raw and using Capture NX 2 to process the images and see if it can automatically correct it for you.
I shoot JPEG continuous. I'm already slowing things down with the High ISO NR option. At ISO 800, I can get away without NR, but above that, the noise is apparent in OOF wood grain and solid panels. Above 1400, it shows up in fur. I turned on High ISO NR and it looks good up to 1600 (the highest ISO I've seen so far.)
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