Dynamic range

slat · Jan 12, 2019

Will a camera with better dynamic range allow you to use a lower ISO? If you were taking shots at night which would be better to have, higher dynamic range or high ISO?

Overread · Jan 12, 2019

I think you're mixing up a few terms.

Dynamic range. If you look at a scene, any scene, there are dark and bright spots of that scene. The difference in stops of light between the brightest and darkest spots is the dynamic range of that scene. How dark or bright they are doesn't matter so much as the difference between the darkest and lightest spots.
Therefore the greater the dynamic range of the camera the greater the variety of scenes it can work in whilst recording usable light.

High ISO. This is essentially boosting the digital signal in the camera which makes it appear more sensitive to light - ergo you get a brighter result at higher ISOs. Higher useable ISOs means more capacity to work in darker conditions with your camera.

It should be noted that on most cameras, raising the ISO often has an impact on the Dynamic range and it will often reduce a bit at higher ISO values.

In general both are desirable features to have and both are useful in many situations so its hard to really make a call on if either one is superior to the other in general. However if you're working at night then higher usable ISO values are a very big benefit and in that case it would be the superior choice.

NOTE Sony ISO Invariance sensors change things somewhat, though I'm honestly not well versed in using them to give a proper commentary on them. This will mostly affect sony cameras and select newer Nikon cameras.

slat · Jan 12, 2019

Thanks for the response. I understand the relationship better now. If you were shooting a scene at night and a camera didn't have a good dynamic range maybe you would have to shoot at ISO 3200. If you had a camera with good dynamic range would you be able to shoot it at say ISO 1600 and get similar results?

480sparky · Jan 12, 2019

Dynamic range isn't equal to exposure. You can have a full, sun-lit beach scene with a 10-stop dynamic range, or a street setting under pole lighting with 10 stops of dynamic range.

ISO of a given camera can affect how much of that dynamic range it can capture. It may be good enough to shoot at ISO 100 and get those 10 stops recorded without blown-out highlights and/or totally black shadows, but crank it up to ISO 6400 and it may only capture 6 or 7 stops of DR.

slat · Jan 12, 2019

So dynamic range kind of gives you more color range in a given scene where ISO is just going to give you the ability to shoot at higher f stops in low light?

480sparky · Jan 12, 2019

Dynamic range doesn't affect color. It's merely the mathematical difference between the brightest and the darkest portions of a scene.

If you have a scene that has, say, an 8-stop DR, you could adjust your settings to expose the brightest part of the scene to be rendered 'correct' in the final image. Adjust your camera to increase the exposure 8 stops, and it will render the darkest part the same 'correct' exposure.

480sparky · Jan 12, 2019

Let's try this: Here's a scene. It has a lot of dynamic range to it. I'm just going to toss numbers out since I don't know what, exactly, the true numbers were since I took this 3 years ago. But let's just use this as an example.

Let's say you want to photograph this scene, and want to know what the dynamic range is in it. You pull out a spot meter (or, if your camera has that feature, you set the internal meter to SPOT). You scan the scene for what you think is the darkest portion of it. You aim your meter at where the blue circle is and you come up with an exposure of ISO 100, f/8 at 1/2 second.

Now you look for the brightest part (the red circle). You meter it, and come up with ISO 100, f/8 at 1/500 second.

I used ISO 100 and f/8 for both exposure to simplify the math. Starting at 1/2 sec, if you decrease exposure by 1 stop, you have 1/4 sec. 2 stops = 1/8. 3 stops at 1/15. 4 stops at 1/30. Five stops for 1/60, six stops for 1/125, seven stops at 1/250 and 8 stops at 1/500, which is the shutter speed for the brightest portion of the scene.

The dynamic range of the scene would then be 8 stops. If you took two images, one at ISO 100 f/8 1/2 sec and another at ISO 100 f/8 1/500 sec, the first exposure would render the area in blue the same brightness as the red area would be in the second shot.