Why Dynamic Range Matters and What to Look For
/Over the decades that I have been a photographer, the amount of dynamic range delivered to us by our tools has increased pretty significantly. Dynamic range is the number of variants, using 1 stop as the metric between blackest blacks and whitest whites. While analogous to the Zone System, they are not the same thing.
Film
When I started photography, I was shooting film. At the time it was predominantly black and white film for prints, colour film for transparencies, and where prints were to be the general output, colour film for prints.
Working with films like Ilford FP4, Kodak Pan-X, Ilford HP4 and HP5 and Kodak Tri-X and exposing and processing them for their defacto ASA, that we now all call ISO, if I did my job well, I could get as much as six stops of dynamic range. Kodachrome underexposed by ⅓ of a stop, could deliver 6 stops, Ektachrome about 5 stops, and Kodacolor about 5 stops. Fujicolor was the same, Agfa a bit less. When I shot weddings, I only shot Kodak Vericolor first II then III because while it did not give me more dynamic range, it was designed to optimize its dynamic range in the whites, lights and pastels.
Working either in my own darkroom or with a good printing house, I could deliver very usable and pleasing prints. Developed my black and white film and prints myself, but found it more convenient to send out the C-41 colour print and E-6 transparency film for development and when making prints. Kodachrome’s K-12 and K-14 processes were Kodak proprietary and any good printing house could make nice prints from Kodachrome transparencies. I did print from transparencies a bit using the CIBAchrome process, but I did not do it enough to be competent or cost effective.
Why all this history? Because the world for many decades was quite happy with 6 stops of dynamic range and thousands of images went into great periodicals and onto gallery walls that only delivered that level of dynamic range. This was so, even though scientists had determined that the human eye/brain combination could resolve over 20 stops of dynamic range. For what it’s worth, that count is still not defined, depending on the expert quoted, it’s somewhere between 20 and 24 stops of range.
Digital
When the first digital sensors were delivered, thank you Kodak, they could do about four stops of dynamic range. So long as sensors used the CCD design model, they did not get much better than 6 stops, about equivalent to common film stocks.
When the internal design of sensors changed to CMOS, the ground shifted and we started to see sensors capable of more dynamic range. Today, we find sensors capable of delivering up to 14 stops of dynamic range, which is absolutely wonderful, but this development evolution changed some other things.
Impact on the Zone System
For serious professionals living and working in the construct of the Zone System, there were now sensors that offered greater dynamic range than the original 10 Zones, necessitating changes in the Zone System to be completely balanced with high dynamic range sensors.
The Life and Death of HDR (High Dynamic Range)
Many photographers will remember the excitement of the design of HDR. One would take multiple exposures at different exposure values, some under, some over, and at least one on target and then use software to combine the images. The algorithms would take the best highlights, the best midtowns and the best shadow elements and combine them into a single image. The original software needed lots of images, with educators recommending 7 or 9 images and a minimum of 5. Cameras were introduced with automatic bracketing functions where you could select the exposure change between images and the number of images to be taken. Most cameras offered a range from 2 stops under to 2 stops over. but some would go as wide as 3 stops under to 3 stops over.
There was a lot of recommendation about making more images at smaller intervals, but there was no real difference whether you used ⅓ or ½ or even full stop intervals for the middle tones. The camera sensors easily handled a one stop variance. Where HDR did help was at the edges. If we look at the +3 -3 option, we could ostensibly extend the dynamic range up to 12 stops which was at the time of normal six stop dynamic range was a huge option. At the time, there were also many templates for the HDR software and many photographers hated the contrasty crunchy look of that kind of HDR after everyone and their cat did it.
As sensor dynamic range increased, the need for HDR diminished, or at least the use of the process did and most HDR software has moved exactly nowhere in the last five years. If your sensor natively offers 12 stops of dynamic range and the image looks awesome, and the software has not changed, why go to the hassle for questionable results of an 18 stop dynamic range image. Some folks still do HDR, but for many, it’s been left in a ditch at the side of the road.
Current State
When your camera sensor has 12 or more stops of dynamic range, you now need to take into account how you will see it. Consider a common computer display that does sRGB at 100%. That is an 8 bit space, so your 12 stops have to fit into 256 levels. Moreover, sensors are non linear, meaning there are more bits in the whites than in the blacks. Can you actually see the difference between 8 stops and 12 stops of dynamic range on an sRGB display? The scientific answer and the emotional answer are frequently different.
We have thus seen the development of displays capable of handling the RGB colour space which is 16 bits and has 65536 levels in which to represent your 12 stops of dynamic range. Better definitely and yes you can see a big difference in the subtle changes. However, we also have to remember that our common sensors at best deliver only 14 bit deep images, and some cameras even allow down stepping to 12 and even 8 bit RAW files. JPEGs are always 8 bit and their massively lossy compression doesn't even get them into the distant car lot at the ball park itself
So a tip follows; If you shoot in JPEG any bit depth over 8, screen colour support beyond sRGB and any dynamic range beyond eight stops in the sensor goes completely unused. Moreover, standard JPEG discards well over 90% of your image data on first file write. You may as well use crayons.
Megapixel Relationship
I recently had an online conversation with a very nice fellow who was wondering why professional photographers tended towards cameras with lower megapixel counts than the higher count sensors. He was under the impression that more megapixels meant more dynamic range. I was sorry to burst that balloon, but let’s be clear. Dynamic range and megapixel count are completely unrelated. There are reasons to choose high megapixel sensors and reasons not to do so, but dynamic range has nothing to do with that.
I do however, encourage discovery of the dynamic range of the sensor in any camera that you consider and buy the greatest dynamic range that fits your use cases and your budget. You don’t have to use all of it, but you cannot add more after the fact (remember that HDR software has been in a static state for years)
Conclusions
My premise is that you enjoy photography and want to make the best images that you can. No camera makes the image, you do, and for the most part, a tool used well is always preferable to a fancier more expensive tool not used to maximize it. in my experience and opinion, the dynamic range of the sensor is a primary driver of camera choice as its functional brightness range. I want a sensor with lots of dynamic range that works in incredibly low light and incredibly bright light. Megapixel count isn’t in my A list of priorities. It’s on the B list because I make large prints. If I did not make large prints or only viewed images on a display of any kind, the megapixel count would not matter one iota.
Thanks as always for reading. If you shop with B&H Photo Video, please use the link on my site as it pays me a small commission and costs you nothing extra. Please feel free to post comments or questions. Until next time, peace.