I have found that vertical banding is terribly apparent in CR2 RAW files from high-end Canon SLRs at the artifical "lowest" ISO setting of ISO 50 - especially if you do any sort of post processing. I am a believer in the concept of using the "digital darkroom" to finisih my images, having leared the art of photography 20 years ago from my father in an actual wet darkroom. I shoot in the field with Photoshop in mind - in terms of dodging and burning and highlighting certain areas of my images, while simultaneously muting others in an attempt to capture the viewer's eye and lead it through the image to areas I want to emphasize.
With today'smodern equipment, we have tools available to us that photogaphers even ten year ago would salivate over. With great power comes great responsibility - and in the case of using the digital darkroom - one must be aware of the consequences of camera settings and how their imapct on your images can be multiplied by your post-processing approach.
Let's look at an example of a photograph I made at my home on Lana`i, Hawai`i at the Kaumalapau small boat harbor one evening in November 2012 (above).
Muted high clouds were pervasive on this day, so I knew before I even took my camera out of the bag that I would probably be seeking a combination of wave action on the tide bench along with moody clouds above the horizon in the far-ground to try to create an image that captured the atmosphere along the coastline. To expand my dynamic range, I used a soft 0.6 stop graduated ND filter from Lee Filters.
At first glance on a screen, you might think the above image was a success. But what happens when we take a look at the area in the red box at 100%?
Horrible vertical banding! Let's dissct the technical details and examine how I got to the finished product from the RAW file, and then ascertain where the banding cmoes from and how to avoid it.
This image was shot at ISO 50, f/13, 0.8 seconds, with a Canon 5D Mark III body and a 16-35mm f/2.8 L II lens. For post processing, I edited the RAW file in Lightroom, then in Photoshop I converted it to monochrome with NIK Software's Silver EFX Pro 2 plugin.
For development settings in LR I used the following in the first step:
In Photoshop, I used two different layers of SilverEfx Pro 2, one for the sky and one for the foreground. Some might say this is HDR; I would disagreee since I am starting off and staying with one "negative" file to get to my end result. To me this technique is a modern equivalent of dodging and burning, and one that I frequently employ to finish images (but not for images that I submit to National Geographic - they still insist processing the same file twice and blending any aspect of it with itself - color, exposure - sharpeness - is unacceptable).
In short - I pushed this image, but not to a level that is uncommon. And - banding! So what could possibly be the problem? Turns out I blew it when I made the exposure by using the artifical ISO setting is ISO 50. The lowest setting on a Canon sSLR is ISO 100. The "low" setting is actually fake, and produces - yup, you guessed it - pronounced banding. Couple the ISO 50 with a) high-grade optics, b)realtively narrow aperture, and c) moderate post processing with emphasis on contrast and structure and banding will rain down from above and ruin the skies in your photographs.
So beware - avoid the "in-between" ISO settings and stick to the native ones (100, 200, 400, 800, 1600, 3200).
Areas in images with low contrast gradations such as clouds / sky will show pronounced banding.