Introduction

In previous tutorials, we discussed what the optimal shutter speed and aperture setting should be when we are shooting HDR photography. Now, we are going to discuss the optimal ISO setting. In HDR photography, we are combining multiple exposures to create one final HDR image. This process of combining exposures automatically creates certain challenges, one being the overall grain in the final HDR image. When you shoot at your camera’s lowest native ISO, you will still see a little bit of grain in your images. Because of this, always keep your ISO at the lowest native ISO on your camera whenever possible. For Canon users, the lowest native ISO is 100. For Nikon users, the lowest native ISO is around 160. In this article, we will discuss reasons why the optimal ISO setting in HDR photography is the lowest native ISO on your camera. In addition, we will also explain what native ISO means.

What is Native ISO?

Your camera has native ISO settings that are multiples of each other. On a Canon, like the Canon 5D Mark III below, the native ISO settings are 100, and then 200, 400, 800 and 1600.

On a Nikon, like the Nikon D800 below, the native ISO settings are 160, then 320, 640, and so forth.

Anything in between these native ISO settings are digitally enhanced settings. For example, at ISO 250, your Canon will take ISO 200 and digitally boost the overall brightness to create ISO 250. ISO 250 will actually yield more grain than if you were to shoot at ISO 400 and pull it down in post production. When you shoot at in-between values rather than going up to the next native ISO, it will reduce the overall image detail and dynamic range. Therefore, if you need to boost the ISO, always increase to the next native ISO setting.

For best HDR image results, stick with ISO 100 on a Canon or ISO 160 on a Nikon. If you need to boost up the ISO, you can go up to ISO 200 or ISO 400 (Nikon equivalence would be ISO 320 or ISO 640). However, before processing your image, you must first reduce the noise of the base images so that there is not too much noise in the final HDR image. ISO 400 is essentially the peak of yielding professional HDR images because at ISO 400, we have to do a significant amount of noise reduction before we process the images. Remember that when you are doing a bracketed sequence to shoot an HDR image, you are taking multiple images and layering them all on top of each other. This means that if you shot at ISO 400, your final HDR image will not look like it was shot at ISO 400 since you are essentially layering 3 times ISO 400 to create the final HDR image. Instead, your final HDR image may look like it was shot at ISO 1600, ISO 3200, or even ISO 6400. The image will basically be unusable unless we go in first and reduce the noise before we process the image. If you shoot at ISO 800 or ISO 1600, your final HDR image will turn out nowhere near what you want. This brings us to reasons why we need to shoot HDR images at the lowest native ISO setting.

#1: Loss of Detail

The first reason why we need to shoot HDR images at the lowest native ISO setting is pretty simple. When we raise the ISO, we introduce noise and grain into our images. Noise and grain will kill the detail in your image, especially when you need to layer multiple exposures to create that final HDR image.

#2: Reduction in Dynamic Range

When you raise the ISO, this will actually reduce the dynamic range in your images. At ISO 100 on a Canon 5D Mark III, we can capture around 12 stops of dynamic range. However, as ISO increases, the dynamic range is greatly reduced and we will no longer be able to capture the scene at 12 stops of dynamic range. Since we are shooting high dynamic range (HDR) photography, increasing your ISO basically defeats the purpose of shooting HDR images. Therefore, keep your ISO at the lowest possible native ISO setting to maximize detail, color and overall dynamic range in your HDR image.

#3: Limits Single-Shot HDRs

Another reason why you should shoot HDR images at the lowest native ISO setting is because you have even less leeway when shooting a single-shot HDR than when you are shooting a bracketed sequence. With single-shot HDR images, the best result you will get is from ISO 100 because we need to capture the entire tonal range within one single image. At ISO 100 on a Canon or ISO 160 on a Nikon, you are capturing the maximum dynamic range possible within that one single photograph, which is the point of a single-shot HDR. At ISO 200, it starts to limit the overall detail and dynamic range of your single-shot HDR image. At ISO 400, it will be impossible to pull back all the tonal range in your single-shot HDR image because you have lost too much detail to begin with. Therefore, with single-shot HDR images, it is crucial to shoot at the lowest possible native ISO.

Conclusion

Remember that when you increase your ISO, you are not only increasing grain, but also reducing the dynamic range in your HDR image. The whole purpose of shooting HDR photography is to increase dynamic range, so adjusting up the ISO is going to decrease the quality of your HDR images. Whenever possible, keep your ISO at the lowest native value that your camera offers. This will yield the best HDR images because it will preserve the most detail and color. If you are not using a Nikon or Canon, just look in your manual or check online to see what the lowest possible native ISO setting is on your camera. More likely than not, it will be around ISO 100 to ISO 200.