5D mk2 - Low ISO banding and how to avoid it
If you read online forums you may have heard that the Canon 5D Mk2 has a major flaw: low ISO banding. I'd read about the "problem", but nevertheless went ahead and bought one.
Several weeks in, I thought I'd share one of the examples where this has popped up, along with a summary of how to avoid it.
Bangkok by Night 5D mk2 + 17-40mm lens - read the full blog post for more info, but only if you're interested in camera-tech issues!
The main image in this post has minor pattern noise ("banding") in the sky areas. It was the third in a series of 3 shots - the first 2 were clearly underexposed and by the third I thought I'd gotten it about right, but was still off by about 1 stop so its been lifted slightly in post processing. If you look closely at the area of sky at 100% you can see noise arranged in a grid-like pattern (100% below).
The point of this blog isn't to complain about banding - more to identify when and why it happens, and how to avoid it. If you can't really see much of a problem in the 100% crops, don't worry too much - its there, and more evident when looking at a larger surface, but still not anything that should cause major alarm.
What is low ISO "Banding"
The image bellow illustrates the "problem" far more clearly than an example of a "real life" image (such as the main blog image). In this case its a photo that's underexposed by about 6 stops (ie. instead of a 2 second exposure, its a 1/30sec exposure, here caused by switching to live-view while in video shooting mode which automatically over-rides a long exposure setting in manual exposure mode). This seems to be the sort of range that many of the online posts complaining about the problem are taken in. If you look at the image without adjustments (below) you can barely seen an outline of skyscrapers.
Clearly if this type of situation comes into your definition of "problem" then there isn't a camera that will meet your needs. Push any image this far and you'll end up seeing a lot of noise - whether its blotchy noise or uniform pattern noise, it isn't going to be pretty. What is more surprising to me is how much detail is actually hidden in the shadows.
Causes of pattern banding
In ordinary shooting situations, there are times when noticeable banding can occur. These are usually where there is a scene with bright highlights and dark shadows. Even then however, the problem is really only evident when dark shadows are pulled to reveal detail, and even there you often really need to be looking to notice any banding.
Short of Canon admitting that banding actually exists, the actual cause will remain a matter for speculation. The most likely explanation appears to be the arrangement of circuitry results in heat building up in a patterned way. If this is the cause, it's reasonable to deduct that the banding will be more problematic when a sensor heats up through prolonged use such as in video or from long exposures.
From my observations so far (based on using the camera normally for about 3500 exposures) the factors that contribute to banding are generally those that contribute to additional noise in general:
- Severe Underexposure
- Lifting areas of dark shadows
- Prolonged use for video or long exposures, particularly in hot climates
To sum up: Yes, banding exists in the 5D mk2, however exposing properly and avoiding drastic adjustments in images means that the occurence is more of theoretical interest than a day-to-day problem.
The image below is the exposure immediately preceding the main blog image. The full image shows the brightness as captured, whereas the second crop shows what the "problem" area looks like with exposure adjusted by 1 stop.
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