When Choosing a Camera, How do You Find its Dynamic Range?
Dynamic range is one of the most important considerations for choosing a camera in the digital age. If you are not familiar with dynamic range, it is the range of tones that your camera can capture between pure white and pure black. The wider the range the better.
Dynamic range is particularly important to the outdoor photographer because you are almost always trying to capture a wide disparity of tones. An obvious example is a typical landscape, where you face a sky that is much brighter than the foreground. You need a camera that can handle the wide disparity in tones without causing the sky in your picture to “blow out” (turn pure white) or the foreground to turn pure black. As such, dynamic range is a really important consideration when initially choosing a camera.
Nevertheless, if you look through the specifications of any camera, you will not find a defined dynamic range. It would be nice if all camera specs had a line that looked something like this:
Dynamic range: 10.2 stops
But they don’t. In fact, as the remainder of this article will show, the whole subject is kind of a mess.
No Simple Test for Measuring Dynamic Range
As important as dynamic range is, you would think that manufacturers would test all these cameras in some systematic way and tell you how wide the dynamic range is for each model. There ought to be a consistent scale. It seems like they could just take a picture of something with a wide disparity in tones, and then (a) see how dark the tones got before turning pure black, and (b) see how light of tones that camera was able to capture before they turned pure white. They could just measure the difference in f-stops and voila we would have a simple scale for measuring dynamic range.
Turns out, it isn’t that simple.
Some who review cameras have actually tried to create a scale or at least compare different cameras (you will see a couple of them later in this article). The results are wildly inconsistent though. The problem with creating a simple scale to measure dynamic range is with the dark tones. When a camera is attempting to capture really dark tones, the real enemy isn’t having the tones turn completely black. Rather, the enemy is noise. At some point, the noise just takes over and the dark tones become unusable. Therefore, the bottom end of the dynamic range scale isn’t defined by “pure black” but “usable black.” That leads to a lot of uncertainty over when the blacks become unusable.
The measurement of dynamic range gets harder still. For example:
- the dynamic range of a camera is different at different ISO levels. As you increase the ISO level of your camera, the dynamic range actually decreases. This is partially a function of the increased noise at higher ISOs mentioned above.
- The type of file also makes a difference. A Raw file will generally have a larger dynamic range than a JPEG.
- The dynamic range is also affected by different camera settings. For example, many cameras have a dynamic range expansion feature (Canon calls this Auto Lighting Optimizer and Nikon calls theirs Active D-Lighting), which will improve the dynamic range slightly when enabled. In-camera sharpening will also decrease the dynamic range of the picture.
Accordingly, there is no scale accepted by everyone for measuring dynamic range.
Are there other measurements we can look to to compare the dynamic range of various cameras? Sort of.
How Dynamic Range Works in Your Camera
First let’s take a look at how dynamic range works in the camera. That will help show you what you should be looking at to determine how wide a dynamic range a camera will have.
The digital sensor of a camera is divided up into tiny photosites that collect light. The photosites create pixels in your picture. Each photosite is essentially a bucket that collects light photons. If the bucket is empty, the pixel is black. As you add light photons, the bucket starts to fill up. When the bucket is full, the pixel is completely white. Adding more light photons once the bucket is full won’t change anything, since it is already pure white.
The idea is to have a large bucket to hold a lot of light photons. The more your bucket can hold, the greater the distance between black (empty) and white (full). Therefore, the dynamic range is increased.
How do you have a larger bucket? By having larger pixels.
How do you have larger pixels? By having a larger image sensor. A smaller sensor can have less pixels to keep the pixels large, but then you might run into resolution problems.
What We’ve Learned So Far
Let’s stop here and consider what we can take away from the discussion so far. There are actually a few important things here. While we don’t have a test or a number that defines dynamic range for us, we now know what defines the bottom end and the top end of the scale:
- The bottom (black) end of the camera’s dynamic range is defined by the amount of noise generated by the sensor. Therefore, the low-light performance of the camera will be what you should look to in determining this point.
- The top (white) end of the camera’s dynamic range is defined by pixel size. Since this is determined by the size of the sensor, you will want to look at sensor size to determine this point.
That leaves us with low-light performance determining the low (dark) end of the range, and sensor size determining the high (bright) end of the range.
When buying a camera and thinking about dynamic range, these are two things you are already probably considering. If you are looking to gauge the dynamic range of a camera though, these are two items to check right away.
More Criteria for Measuring Dynamic Range
The dynamic range of a digital camera is also determined by the bit-depth of your camera. Each pixel has a certain number of bits. The more the better. Think of each bit as a switch, and the more switches you have, the more color options are available in each pixel. That means you can have more tones of various colors.
Jpegs are generally 8-bit files, and Raw files can be up to 16-bits. Because the measurements involved are logarithmic, the difference between an 8-bit file and a 12-bit file is enormous. For more information about the differences in bit-depth, check out this article. For now, the point is that you should check the bit-depth of the camera you are considering purchasing.
In practice, the bit-depth will probably not result in any changes in your camera-buying decision. Almost all DSLRs have bit-depths of 14. Mirrorless cameras with APS-C or full-frame sensors are also generally 14-bit. Some Micro 4/3 cameras are 12-bit though.
Comparisons of Dynamic Range
There are 2 different companies that have conducted comprehensive tests of the dynamic range of the digital cameras on the market. They are called DxO Mark and Digital Photography Review (DP Review). Neither is perfect, and both lead to some pretty significant questions (which we will get to later). In any event, the remainder of this article will be the results of these sets of testing. Let’s check them out now.
DxO Mark Comparisons
First, here are the results of the dynamic range testing done by DxO Mark (I will discuss the results below):
From the results of DxO Mark it appears, as we might expect given the discussion above, that a larger sensor gets you a larger dynamic range. Cameras with Micro-4/3 sensors averaged about 12.5 stops of dynamic range. Cameras with APS-C sized sensors averaged 12.9 stops (an increase of just under 1/2 a stop), and full-frame cameras averaged 13.25 stops (another increase of under 1/2 a stop). This is hardly a dramatic change, but it is definitely worth considering.
There is also a mild correlation between the price of the camera and the dynamic range. In general, the more you pay, the higher the dynamic range. That is also to be expected.
There is a significant potential problem with the DxO Mark data though, and that is how it treats different manufacturers. DxO Mark consistently scores Nikons really high, and rates Canons really low. You can see that in this chart, but it is even more glaring when you look closer at the DxO Mark data. Consider:
- In its dynamic range scoring, DxO Mark places Nikon cameras as 7 of the top 10 cameras tested (including the top 5). DxO Mark has Nikon cameras in 20 of the top 50 spots. How many Canon cameras does DxO Mark have in its top 50? Answer: 0. That’s right, not one of the top 50 cameras. DxO Mark has point-and-shoots and discontinued models rated much higher than even professional level Canon cameras.
- In its overall scoring of camera sensors (which also considers low-light performance and color in addition to dynamic range), DxO Mark has Nikons in 6 of the top 10 spots, and also as 15 of the top 30. How many Canons in the top 30? Again, zero.
Call me a Canon apologist if you want, but this just doesn’t make any sense. Could Nikon have an advangage over Canon in this regard? Sure. But do I find it plausible that Nikon sensors completely dominate Canons and nobody else has noticed or written about it? No I do not.
Don’t get me wrong. I do not think DxO Mark is out to get Canon, or is engaged in some conspiracy. But I do think there is something inherent in their tests that biases in favor of some manufacturers and against others. I do not know anything about the specifics of their tests, but the results, as between camera manufacturer, are wildly inconsistent with everything I’ve ever experienced or heard about these cameras. Further, as shown below, these results are also not consistent with other testing that has been done.
DP Review Comparisons
There other group that conducts tests of dynamic ranges of digital cameras is DP Review. Here is a chart with their results (I will discuss the results below):
A couple of notes on the DP Review chart above before I discuss the results:
- DP Review does not actually create an overall chart showing all the models of camera they have tested. Rather, this chart is something I pieced together by looking at graphs on DP Review’s website.
- You might have noticed that all the latest models of digital cameras are not on the DP Review chart. For example, you will not see the Nikon D810, Sony A7II, or Canon 7D mark ii. Although DP Review has tested over 100 cameras to date, it seems to take them a while to perform these tests, such that many of the most recently-released cameras have not been tested.
The DP Review results generally show the dynamic ranges of current digital cameras clustered around 9. Half of the cameras shown above have a dynamic range within 1/2 stop of 9. All of them have dynamic ranges between 8 and 10.
The testing done by DP Review does not show improvement in the dynamic range of digital cameras with larger sensors. If anything, the cameras with the smaller sensors tend to have higher dynamic ranges. That is directly contrary to the testing from DxO Mark.
In addition, DP Review does not score Nikon significantly higher than Canon. If anything, Canons fare better than Nikons in the DP Review testing.
Comparing the Testing Results
So where does that leave us? In a bit of a jumbled mess, obviously. Here is a comparison of the testing results done by DxO Mark and DP Review:
- There is no consensus as to the actual dynamic range of most digital cameras. DxO Mark puts most cameras between 12 and 15 stops; while DP Review only shows dynamic ranges of 8 – 10 stops.
- There is no consensus as to the impact of a larger digital sensor. In theory, this should have a big impact. DxO Mark shows such an impact. The testing by DP Review, however, does not.
- There is no clear correlation between price and dynamic range. While DxO mark shows a mild correlation between price and dynamic range, DP Review actually shows a mild inverse correlation.
- The impact of the camera manufacturer is unclear as well. As mentioned above, DxO Mark shows Nikons significantly outperforming Canons. DP Review actually seems to rate the Canons a little higher than the Nikons. Both have Sony doing reasonably well.
Dynamic range, while important, is a tricky thing to get your arms around. Without a uniform standard or spec from the manufacturers, it is difficult to compare models. Further, because of the inherent fuzziness in the results, even when you see testing results they are subject to being questioned. As the testing by DxO Mark and DP Review shows, there is just not a consistent scale, and neither is there any consistency between the testing.
Hopefully the information above helps you compare specific models you might be considering. If the model you are considering buying is not on my charts, you can still look to other factors to gauge how the camera should perform. Start by choosing the sensor size you want, then review any low-light performance tests, and make sure the bit-depth is in line with other models (generally 14 as I write this). But remember that dynamic range is one consideration of many, and move on to the other aspects that are important to you.