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01-19-2009, 08:49 AM   #1
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Pretty in Pink.. and Green?

I was shooting brackets and this popped up rather consistently throughout. The camera is new to me. In fact it is a refurbished K10D that I was giving a test run on. Unfortunately my primary is out for service so I couldn't baseline this against another camera.

It happens most in overexposed photos, but also seems to occur in small areas of overexposure in uncompensated frames as well. The RAW file have it as well as the JPEGs.

Any Clue as to what this is? Has anyone experienced this?

Lens is a Tamron 28-75mm f/2.8. I've shot a lot of brackets with it and never experienced this. I'll try another lens if I can reproduce this on the Tamron.

Thanks for any help you might be able to give.

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01-19-2009, 10:53 AM   #2
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You are shooting a back lit subject, which will point up every flaw in your lens. The things you see in red and green are Chromatic Aberration - the lens does not focus the colours all at the same point. A lens works like a complicated prism, and actually spreads the frequencies.

There are lenses that do not do this as much as others. They have some very expensive pieces of glass in the formula that greatly reduce the spread of the colours. These are marked with letters and a much higher price tag.

The CA can be reduced somewhat by stopping the lens down. I own a Pentax M 400/5.6 which has a bad CA with red fringes showing up in back lit subjects - example is the mule deer doe in my Flickr M 400 set. I find that stopping down as little as one stop to f/8 the aberrations are greatly reduced.

Most post processing programmes have tools that reduce the effort to remove the CA and Purple Fringe (sensor based aberrations).

By the way, those CAs are much worse than my M 400/5.6 when I do the same thing. I don't get the green side at all, only the red.
01-19-2009, 03:29 PM   #3
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Reminds me why I never buy Tamron lenses...
01-19-2009, 03:36 PM   #4
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I think this is much more than the lens. it might contribute some of the colour shifts but this is extreme. Those are huge blotches of colour in a small web shot. I think the sensor has a serious issue. Can't say what but send that one back IMO.

01-19-2009, 03:45 PM   #5
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Yeah, I know... I just can't let the chance slip to knock the competition
01-19-2009, 03:49 PM   #6
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QuoteOriginally posted by Peter Zack Quote
I think this is much more than the lens. it might contribute some of the colour shifts but this is extreme. Those are huge blotches of colour in a small web shot. I think the sensor has a serious issue. Can't say what but send that one back IMO.
i'd have to tend to agree with this..
01-19-2009, 04:28 PM   #7
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QuoteOriginally posted by Peter Zack Quote
I think this is much more than the lens. it might contribute some of the colour shifts but this is extreme. Those are huge blotches of colour in a small web shot. I think the sensor has a serious issue. Can't say what but send that one back IMO.
I have to disagree, Peter. The artifacts are only in the areas with severe backlighting. The twigs against the snow at the bottom show no CA. Purple is generally sensor results. It may be that the particular lens is a very bad copy, but those are lens sourced CA.
01-19-2009, 04:43 PM   #8
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CR you may be correct. I can't recall seeing anything this glaringly bad though. I'd like to see the full sized image if possible. Maybe some test shots with another lens. I'm not defending the lens. My Tamron 28-75mm crapped out and isn't worth fixing. But it was never this bad for the 1 1/2 years I used it before the failure.

01-19-2009, 05:14 PM   #9
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Yellow

I've had the Yellow channel blown out and it produces some odd results when I put it thought AdobeRAW. However I understand it is a problem with some old AMD processors.

I'm not sure if this is related, I just can't see a lens being that bad on its own.
01-19-2009, 06:12 PM   #10
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Honestly, I've never seen anything this crazy with my other body and this lens and I have taken backlit shots a lot. I think I'd have noticed this kind of thing before. I've had CA before but never like this. Unfortunately the other body is in the shop for a cleaning.

This copy of the Tamron was actually serviced by Tamron a short while back and it is very, very sharp and seems dead on. I've posted many pics with it. Never seen anything approaching this with it.

Like Peter said, the CA is just too big. Oh, and I'm using Intel here.

The full size version is available at the following link. Right click it and save as:

http://seaaingray.zenfolio.com/img/v6/p1036790138.jpg

Here's a larger size to view. Photo taken at f/6.7 1/20th, 50mm.



Seaain

Last edited by woof; 01-19-2009 at 07:50 PM.
01-19-2009, 07:51 PM   #11
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That's insane. If it's just CA it's by far and away the worst I have ever seen.
01-20-2009, 09:31 AM   #12
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Another thought comes to mind - did you have a filter on the lens when you took the image? If so, try the same shot in the same lighting without it. One never knows. The entire bright area appears to be almost directly into the sun with thinner cloud. The brighter the background the more pronounced the CA, I have personally noticed. My back yard faces an acreage and is oriented due South.

I almost had a panic attack when I saw the CA from my 400 until I figured out that shooting wide open into the sun was not the best orientation for the lens. The sample shot with CA is on my Flickr site here SMCP=M 400/5.6 wide open.
Flickr Photo Download: K10D Mule Deer Doe 400_5.6-11

This is the original upload - a full size jpeg. Please note that the background is simply brightly lit snow, not brightly lit cloud. If I spot a more comparable shot from my back of the house, I'll stick it up here. I expect the CA to be enormous in that situation.
01-20-2009, 05:53 PM   #13
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QuoteOriginally posted by Canada_Rockies Quote
Another thought comes to mind - did you have a filter on the lens when you took the image?
Initially yes. However, the picture shown is the test shot after I removed it.

Good thinking - THANK YOU. I appreciate your thinking about this. I ** really ** do.

As I previously said, the other body is now in the shop. While not the same exact shooting conditions, but the weekend before I sent the other body in I shot a whole bunch of basically backlit shots of trees with ice and got nothing even resembling this. Same lens. No CAs at all.

Either way I cannot prove this. The bad one was shot at f/6.5 all my others from the other shoot are significantly stopped down from there.

Given the time of day of the offending lighting conditions, I'll just have to wait until this weekend and take a bag 'o lenses out to my driveway and reproduce this against several lenses to see the results. If it is sensor based I'd expect to see it over and over no matter what lens. If not, I'd expect less or even no CAs from some of the lenses. Best I can do without a baseline known and trusted camera.

Eventually I can also test this against my known good and well trusted K10D... once it is back in. That will be a while, but we'll have some pretty diagnostic stuff this weekend. The offending shot was taken at 50mm, so it'll be easy to reproduce with a variety of lenses.

Thanks again. I'll update this when I get more data.

Seaain
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01-20-2009, 06:00 PM   #14
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QuoteQuote:
Lens is a Tamron 28-75mm f/2.8.
This lens is renowned throughout the land as being either REALLY good or REALLY bad. You may just have a bad copy.
01-20-2009, 07:02 PM   #15
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QuoteOriginally posted by woof Quote
Either way I cannot prove this. The bad one was shot at f/6.5 all my others from the other shoot are significantly stopped down from there.

Thanks again. I'll update this when I get more data.

Seaain
woof!
I have noticed that stopping my offending lens down definitely can reduce the CAs - my biggest offender is the oft mentioned M 400/5.6 - and a stop of two makes a world of difference. I look forward to your results this weekend.
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