Chromatic lens aberration

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Chromatic lens aberration

Postby Kellogs on Fri Jun 30, 2006 4:17 pm

This is a subject I know very little about………….. so I’m hoping there are a few experts out there to help

Here is an example of what I am experiencing with my 70-200VR. As you can see this image has been cropped quite a bit.

How common is this and should I be concerned (especially because the lens is only 2 months old)

Image
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Postby pharmer on Fri Jun 30, 2006 4:27 pm

Thats pretty bad - I get less than that on my $150 70-300 Tamron zoom :)

Wouldn't expect that on a 70-200 VR - doesn't look like a very high contrast scene, what f-stop? wide open?
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Postby Kellogs on Fri Jun 30, 2006 4:30 pm

I Know!!!! That's what is worrying me!!!

D200 f3.2 @ 1/500 sec.
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Postby pharmer on Fri Jun 30, 2006 4:34 pm

Kellogs wrote:I Know!!!! That's what is worrying me!!!

D200 f3.2 @ 1/500 sec.


Maybe a combination of factors, very bright scene, high contrast, high saturation mode on the D200, ISO500 and a wide aperature

I recommend not using high saturation above ISO400 - it creates colour noise because some of the colours are out of spec/gammut (over saturated)

D200 produces very vivid colours even at normal or moderate
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Postby gstark on Fri Jun 30, 2006 4:36 pm

That's nothing to do with the lens.

It's an artefact known as purple fringing (I wonder why? :) ) and it generally happens in areas of excepionally high contrast. Typically you will see a blown area adjacent to a darker section of the image - exactly as your image presents.

The cure is to alter your technique so as to reduce the likliehood of this happenning. Use fill flash to increase the amount of light going onto the subject, and then adjust your exposure accordingly. The net effect of this is that you will be reducing the contrast range that your sensor has to cope with, thus helping to aleviate the problem.
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Postby Raskill on Fri Jun 30, 2006 4:46 pm

Yoink!

That was one of the reasons I got rid of my Sigma 70-200 F/2.8.

Quite a few cars with high contrast decals/colour schemes exhibited this. I figured it was the lens and got rid of it. I later thought perhaps the cheap filter I was using didn't help either.

I think it has something to do with the lens not properly focussing all the wavelengths of light onto the sensor correctly. Or some such nerdy thing. Either way, I wouldn't have expected it from a 70-200 VR :shock:
Last edited by Raskill on Fri Jun 30, 2006 4:47 pm, edited 1 time in total.
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Postby gstark on Fri Jun 30, 2006 4:46 pm

Have a look here and here.
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Postby MCWB on Fri Jun 30, 2006 4:49 pm

As Gary says, this effect happens on very high contrast boundaries. In the above picture, the arm is completely blown (255,255,255) and right next to it is a very dark area (down to 40,40,40). You will usually see more of this with higher resolution sensors (like the D200) and more when you're close to wide-open, but you can easily get rid of it in your RAW converter of choice, or PS. :)
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Postby gooseberry on Fri Jun 30, 2006 4:52 pm

What filter (brand and type) are you using in front of your lens ?

Also, as pharmer mentioned, you are using ISO 500, on a D200 with high saturation and your highlights have blown. If you look closely, you can see local blooming which is causing small amounts of the type-1 (short) banding.
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Postby gstark on Fri Jun 30, 2006 5:02 pm

MCWB wrote:As Gary says, this effect happens on very high contrast boundaries. In the above picture, the arm is completely blown (255,255,255) and right next to it is a very dark area (down to 40,40,40).


This is worse even than just badly blown - it's way off the scale! Have a look at the white block adjacent to the elbow - that's a nasty piece of overexposure there, and I would really be looking at ways to narrow the contrast range as my first port of call in addressing the problem with this issue.

With this great a level of overexposure, I'd be adjusting technique before even thinking about a flaw in the equipment. If the image was correctly exposed (or moreso) and this problem continued to exist, then I'd start looking at the equipment, but not based upon the evidence presented in this image.
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Postby gooseberry on Fri Jun 30, 2006 5:04 pm

gstark wrote:This is worse even than just badly blown - it's way off the scale! Have a look at the white block adjacent to the elbow - that's a nasty piece of overexposure there, and I would really be looking at ways to narrow the contrast range as my first port of call in addressing the problem with this issue.

With this great a level of overexposure, I'd be adjusting technique before even thinking about a flaw in the equipment. If the image was correctly exposed (or moreso) and this problem continued to exist, then I'd start looking at the equipment, but not based upon the evidence presented in this image.


Yep, it would seem that the highlights are blown by about 3 to 4 stops, that is how much you have to blow the highlights to start to get the type 1 banding.
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Postby pharmer on Fri Jun 30, 2006 5:04 pm

Raskill wrote:Yoink!

That was one of the reasons I got rid of my Sigma 70-200 F/2.8.



This lense is no worse than the Nikon with CA issues - the only lenses I've been able to get CA on are ultra cheap plastic zooms (70-300) and the Tokina 12-24.

You have to overexpose in very contrasty condidtons to get CA
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Postby johnd on Fri Jun 30, 2006 5:25 pm

pharmer wrote:
Kellogs wrote:I Know!!!! That's what is worrying me!!!

D200 f3.2 @ 1/500 sec.


Maybe a combination of factors, very bright scene, high contrast, high saturation mode on the D200, ISO500 and a wide aperature


I don't think Kelly mentioned ISO500. She did mention 1/500 sec exposure time. But I agree, very high contrast with blown highlights will do it. And as someone has already mentioned, your raw converter should be able to help (assuming shooting in raw).

Cheers
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Postby pharmer on Fri Jun 30, 2006 5:26 pm

johnd wrote:
pharmer wrote:
Kellogs wrote:I Know!!!! That's what is worrying me!!!

D200 f3.2 @ 1/500 sec.


Maybe a combination of factors, very bright scene, high contrast, high saturation mode on the D200, ISO500 and a wide aperature


I don't think Kelly mentioned ISO500. She did mention 1/500 sec exposure time. But I agree, very high contrast with blown highlights will do it. And as someone has already mentioned, your raw converter should be able to help (assuming shooting in raw).

Cheers
John


Its in the EXIF data :)
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Postby nito on Fri Jun 30, 2006 7:11 pm

I dont know what you guys are talking about. Its obviously the glow of the bride on her wedding day. :D

Kellogs, I like your wedding pictures on your HP. :D
Last edited by nito on Sat Jul 01, 2006 10:28 am, edited 1 time in total.
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Postby birddog114 on Fri Jun 30, 2006 7:17 pm

Johnd,
Sorry, I have to say this: Kellogs is a boy.

Kellogs,

I'm with all other previously posters as Gary, Pharmer, gooseberry & MCWB.
Relax and try something difference or with difference setup.
Yes, I spotted small amount of the type-1 banding too.
______________________________________

Or ditch the D200 and lust the D2Xs :lol:
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Postby Kellogs on Fri Jun 30, 2006 8:29 pm

Sorry to say Birddog but last time I looked i was female!!!!
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Postby birddog114 on Fri Jun 30, 2006 8:31 pm

Kellogs wrote:Sorry to say Birddog but last time I looked i was female!!!!


OMG! You have inverted!!!!! :shock:
:lol: :lol: :lol: :lol:
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Postby wendellt on Fri Jun 30, 2006 9:58 pm

what gary said is absolutely right

but you can minimise it by upping your f stop

on my 28-70 at 2.8 any high contrast areas produce fringing

but if i stop the lens down to f4 it reduces it
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Postby Kellogs on Fri Jun 30, 2006 10:09 pm

Thanks everyone for all your great advice. Looks like I won't have to throw the 70-200VR lens out afterall!!!
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Postby Steffen on Fri Jun 30, 2006 10:28 pm

nito wrote:I dont know what you guys are talking about. Its obviously the glow of the bride on her wedding day. :D


Nah, this is what happens when you eat fish from the harbour... :shock:

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Postby Matt. K on Sat Jul 01, 2006 12:07 am

Kellogs
Could you please post the entire image so I can see the extent of the CA in relation to the image size?
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Postby nito on Sat Jul 01, 2006 10:27 am

birddog114 wrote:
Kellogs wrote:Sorry to say Birddog but last time I looked i was female!!!!


OMG! You have inverted!!!!! :shock:
:lol: :lol: :lol: :lol:


Actually birddog, its the other way around. We were all inverted, but some became expansive instead. :shock:
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Postby Big Red on Sat Jul 01, 2006 12:01 pm

nito wrote:
birddog114 wrote:
Kellogs wrote:Sorry to say Birddog but last time I looked i was female!!!!


OMG! You have inverted!!!!! :shock:
:lol: :lol: :lol: :lol:


Actually birddog, its the other way around. We were all inverted, but some became expansive instead. :shock:


you have put an Image in my mind of a production line and a bike pump ...
ewww :shock:
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Postby Kellogs on Sat Jul 01, 2006 1:39 pm

Here it is.................

Please ignore the composition and resolution. It’s an image I wasn’t planning on keeping.

Thanks again everyone!!!
:)
Image
Last edited by Kellogs on Sat Jul 01, 2006 2:40 pm, edited 1 time in total.
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Postby Manta on Sat Jul 01, 2006 1:45 pm

Kellogs wrote:Thanks everyone for all your great advice. Looks like I won't have to throw the 70-200VR lens out afterall!!!


Of course you have to throw it out! Just let me know when and where... :twisted:

Looks like you've got some good advice here Kellogs - I'm sure it will help in the future.
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Postby MCWB on Sat Jul 01, 2006 3:19 pm

Kelly,

Just a quick Hue/Sat adjustment, magenta saturation turned right down, and blues and reds down a bit.

Image
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Postby Matt. K on Sat Jul 01, 2006 4:25 pm

Looking at that image I doubt that there is anything wrong with the lens...providing the image is soft because of a slow shutter speed. CA looks normal for that type of harsh lighting and was probably made worse by the slight amount of camera or subject movement. Relax!
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