Exposure Increments


Today’s Question: My camera (Olympus OMD EM1) has settings for both 1/2 and 1/3 F-Stops. It also has settings for full (1 stop) and 1/3 ISO. What is the best combination of settings to use?

Tim’s Quick Answer: The decisions here primarily relate to a choice between more precise control over exposure versus a more streamlined workflow for adjusting exposure settings. Although I’m a self-confessed control freak, I prefer to use half-stop increments for exposure settings and full-stop increments for ISO.

More Detail: Let’s first consider the overall exposure settings, meaning the increments for setting the lens aperture (f-stop) and shutter speed. With most cameras you can choose between one-half stop increments and one-third stop increments.

Opting for one-third stop increments obviously provides you with greater precision in setting your exposure. I would argue that for most photographic situations, that precision doesn’t provide a significant advantage. After all, the incremental benefit in being able to shift exposure in one-third stop increments is only about one-sixth of a stop.

In other words, in the worst case scenario your exposure would be off by about one-sixth of a stop if you used one-half stop increments instead of one-third stop increments. For many (if not most) typical photographic scenarios, an exposure “error” of one-sixth of a stop won’t create any insurmountable problems for the photo.

That said, there are certainly situations where greater precision can be helpful. For example, with a scene that contains extreme contrast, having the ability to adjust exposure in one-third stop increments could help maximize the amount of detail in the extreme highlights or shadows, by virtue of being able to set the exposure with greater precision.

When it comes to the ISO setting, I think it is worth keeping in mind that the primary impact of the ISO setting is noise. Raising the ISO enables you to achieve a faster shutter speed, for example, but at the cost of additional noise in the final image.

Having the ability to adjust ISO in half-stop increments helps ensure you can adjust the overall exposure settings while minimizing the increased noise in your captures. I personally prefer the efficiency of being able to adjust exposure more quickly when it is necessary by adjusting the ISO setting in full-stop increments.

To be sure, raising the ISO setting by a half-stop more than is really necessary for a particular scenario will generally result in more noise in the photo than you could have otherwise expected. I tend to be somewhat conservative with increases in the ISO setting in any event, so to me this isn’t a serious concern. In addition, most newer cameras provide rather good performance when raising the ISO setting to moderately high values.

So, I prefer to use one-half stop increments for my exposure settings, and full-stop increments for my ISO setting. But there are certainly many photographers who prefer greater precision for these adjustments, and I certainly appreciate that perspective. In other words, this largely comes down to a personal decision for each photographer, choosing a balance between precision and the potential speed of exposure setting adjustments.