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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 08 May 2011 (Sunday) 19:21
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Banding issue in sky and light fall off.

 
sanfairyanne
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May 08, 2011 19:21 |  #1

I took the attached shot with a 5DII 24-105L lens, at F4 105mm. I kick myself for shooting at F4, it was a mistake when I inadvertently switched from manual to aperture priority. It was way below zero up here so I can forgive myself for making this mistake. I took the shot on RAW and the picture you´re looking at was converted to Jpeg via ACR.

Firstly there´s dreadful banding in the sky, a problem I´ve had with a number of recent shots taken with that lens, at different apertures.

I´ve some ideas what may be causing it but I´d like to hear other folks opinion.

Also why am I getting such bad light fall off at the corners. I thought the 5DII corrects for this with its CORRECT FOR PERIPHERAL ILLUMINATION.

Unfortunately I am traveling in South America without a computer (internet cafe here). I´m hoping my lens isn´t faulty because the 24-105 gets the most use and I am only part way through my travels.

Many thanks.


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jaycky
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May 08, 2011 19:25 |  #2

Is this straight out of the camera?
I have never had this out of the camera but have had it after you push PP...


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Sdiver2489
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May 08, 2011 19:41 |  #3

are you talking about the circular color banding? Looks like too much compression to me


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xarqi
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May 08, 2011 19:53 |  #4

I doubt if the problem is with your lens as I can't imagine how a lens could cause these symptoms.

I'm not familiar with the peripheral lighting correction, but it could be something that applies only to in-camera processed jpeg images, and so would not be included in the raw file, other than possibly as a flag to say it had been selected.

I agree with the comment above, that the banding looks like a compression artefact, or perhaps, an issue with bit depth. Posting the raw file somewhere may allow us to investigate better.




  
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sanfairyanne
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May 08, 2011 20:05 as a reply to  @ xarqi's post |  #5

The banding is immediately noticeable on the LCD screen on the camera, if that helps.

It was suggested that the problem was to do with bit depth, something as a beginner I´m pretty vague about. I was led to believe their may be too many shades of blue in the sky for an 8 bit depth to cope with. If this is the case it seems a bit poor to me that I can´t take pictures of the sky with a $2800 camera.




  
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sanfairyanne
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May 08, 2011 20:08 |  #6

Xarqi sorry I can´t upload the RAW file, I´m on modem speed here in southern Patagonia.




  
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xarqi
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May 08, 2011 20:39 |  #7

The preview on the LCD is a jpeg produced in the camera, so it doesn't necessarily truly reflect the raw data.

Stay tuned - I expect someone who knows far more than me about this will be along soon. Meanwhile, just keep shooting raw, and you'll have the best chance of fixing any problems.




  
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sanfairyanne
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May 08, 2011 22:26 |  #8

Xarqi,

I kind of figured it must be the case that the camera throws out a Jpeg repro´for the LCD screen. For me it´s weird that this problem seems to have only recently materialised. I can´t think of anything I might have inadvertantly set on the camera that would cause this. It´s nearly 1.00am now, I´m going to get back on line in the morning.
Please if anyone has any advice I would really appreciate it.




  
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Bendel
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May 08, 2011 22:57 |  #9

I've also had circular banding in the sky with a 5Dc and a 24-105. It appears in raw file as well.


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sanfairyanne
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May 09, 2011 06:32 as a reply to  @ Bendel's post |  #10

Ok I´m not alone, I´m just trying to keep this thread alive, so if anyone has anything to say now´s the time.




  
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Monito
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May 09, 2011 06:37 |  #11

It's due to underexposure. At low bit levels, there are fewer gradations available. One channel is very low and the other two are black in that sky.

For example, from 8 to 16 there are 8 gradations. From 64 to 128 there are 64 gradations. That's a huge difference.

It's yet another reason to EttR: Expose to the Right.


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Monito
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May 09, 2011 06:40 |  #12

EttR: Expose to the Right on the HistoBlinkyMeter. Push the exposure to the right but make sure it doesn't mound up there and make sure that no important highlights are blinking. Then in post processing push the tones back down to where they should be aesthetically.

The benefits are much less noise in the shadows and less banding in deep blue skies.

If you have more exposure on the sensor, the other channels start registering tones to make the overall tonal value in blue sky lighter. When there are variations in multiple channels and higher bit levels in the primary channel, then there is much less or non-existent banding.


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Keyan
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May 09, 2011 08:17 |  #13

The RAW file will NOT have the vignetting corrected by the CORRECT FOR PERIPHERAL ILLUMINATION option, so if you just take a RAW file and then convert it straight into jpeg the light falloff will still be there. You need correct RAW files in post. I believe DPP can do it, as can DxO or Lightroom.


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melcat
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May 09, 2011 08:22 |  #14

Monito wrote in post #12374798 (external link)
It's due to underexposure. At low bit levels, there are fewer gradations available. One channel is very low and the other two are black in that sky.

For example, from 8 to 16 there are 8 gradations. From 64 to 128 there are 64 gradations. That's a huge difference.

You appear to have the idea that a raw file is 8 bits per channel. That is not the case - it is 12 or 14, depending on the camera, probably 14 for the 7D. That's why you *can* get away with correcting slight underexposure when converting from raw.

Most likely these images will be OK when properly postprocessed at home.

Of course the camera is designed to produce acceptable results when shooting low key images.




  
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sanfairyanne
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May 09, 2011 09:17 as a reply to  @ melcat's post |  #15

I hear what is being said, expose to the right just before highlight clipping so you have detail but nothing blown out. Then pull back in post.

I´m looking at another shot where I´ve bracketed three times. I think only the under-exposed image is showing banding.

Just taken a few test shots, under-exposing the sky and no banding, typically it only happens when you´ve spent a dozen nights sleeping in minus 10c waiting and waiting for a shot.




  
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Banding issue in sky and light fall off.
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