People sometimes ask me what kind of camera they should buy. A short time later, they start asking for explanations of what all the “features” do and their relative importance when choosing a camera.
Ok, so here’s the thing: there are many things to consider when purchasing a camera—resolution, FPS, flash sync speed, etc. One thing I think novice camera buyers fail to fully appreciate is the dynamic range of whatever sensor is housed inside a camera body. What is this dynamic range of which I speak? Allow me to pontificate.
One definition of camera sensor dynamic range is provided on the DxOMark website. They define it as: “the ratio between the highest and lowest gray luminance a sensor can capture. However, the lowest gray luminance makes sense only if it is not drowned by noise, thus this lower boundary is defined as the gray luminance for which the SNR is larger than 1. The dynamic range is a ratio of gray luminance; it has no defined unit per se, but it can be expressed in Ev, or f-stops.”
Right. Got it.
Actually, I think it’s a fine definitional statement. For those of us with only a few functional neurons, however, I humbly offer a simplified alternate explanation. I have little fear in doing this, as I know that readers of internet blogs have traditionally been among the most compassionate and friendly of audiences to ever participate in human interactions. So here we go…
Imagine you’ve got thirteen cats in a line. On the right is a pure black cat, and on the right is a pure white cat, and all the ones in the middle form a spectrum of gradually increasing or decreasing grayness. The number 7 cat is a pure mid-tone grey—how convenient. The dynamic range of your sensor dictates how many of these cats you can capture in a single exposure with reasonable detail.
If, for example, your sensor has a very wide dynamic range, you may be able to capture detail in all of the cats including the fine silky hair of the black cat and the delicate patterns of the white lace on the white collar of the white cat—but you would need a very good sensor indeed for all of those hypothetical cats. More realistically, the cameras I own and operate, for example, can capture most but not all of those cats. Let’s take a wild guess and say 8 or 9 of them with some reasonable amount of detail. Which 8 or 9? Well, the good news is that I get to have a little bit of input into that. I can, for example, decide the black cat isn’t very important and abandon him to the shadows. I can decide that the grey cat is most important and allow both the black and the white cat to get blown out. Get it?
Some examples:
First, the same shot as my last post. Now take a look and identify the darkest and the lightest spots in the photo. Those are clues to the shot’s dynamic range. While taking this shot, I was concerned mostly about how bright the moon was relative to the other important parts of the shot. I wanted a nice shot that showed both the detail in the moon and some detail of the buildings and vegetation. If the moon was too bright, I wouldn’t get it. Turns out I was ok, because the moon had just risen and was still relatively close to the horizon. It wasn’t at full brightness yet, probably due to atmospheric haze. Looking at the histogram of the shot, I realized that I was capturing all of the shot’s dynamic range that I cared about. Go me.
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| Full moon rising over Washington DC skyline; the Lincoln and Washington Monuments; and the U.S. Capitol Building, February 2013 |
Next, same shot, but a few minutes later after the moon had risen and had really brightened (remember, the moon is essentially reflecting full daylight). This (unprocessed) shot is now pushing the dynamic range of my sensor and, therefore, forcing me to make some “artistic choices” about the shot. Abandon the darker shadows and get a nice moon shot? Let the moon get blown out and keep the detail in the bottom half of the frame? Lose all self-respect, bracket it, and run it through HDR software (don’t think I won’t do it either).
So, here’s the moral of the story: When considering the purchase of a new camera, check out the dynamic range and integrate that into your decision. I recommend you check out the DxOMark website which gives their estimates of dynamic range for various sensors. For example, they list 11.3 stops of dynamic range for landscape for a Nikon D3100, but they rate a Nikon D800 at 14.4. Assuming these measurements are accurate, that’s almost three more stops of exposure for your shot.
Yes, more DR will probably cost you more money. No, you don’t need the most DR available to take good photos. Yes, the Nikon D3100 is a great camera and you should be proud to own one. This is just something to think about.
Warning: Engage brain before pressing shutter button.
