A Little Lesson on Aperture and Depth of Field

These days, I am helping with an online mentorship where we teach some beginners about the technical foundations of photography (aperture, shutter speed, ISO, that kind of stuff) and how to get their cameras out of Auto mode. Each week, to let the students exercise their newly acquired knowledge we give out an assignment that involves taking some photos.

This week, the topic of the lesson is the use of flash. While reviewing some of the submitted photos, I noticed that some people were taking photos with flash at apertures as small as f/22. I explained why that is rarely a good idea and asked why they were trying to achieve by using such a small aperture. A conversation ensued, and somebody asked the following question:

People are usually looking for more depth of field, no?

I took the time to explain why maximum depth of field is not an absolute goal that must be achieved at any cost. Then I thought my answer would make for a good blog post, so I copied it here, slightly edited, for the benefit of all my readers. Here’s hoping someone will find it useful.

This also made me think that sometimes we focus too much (pun not intended) on the “how” and not enough on the “why”. It is good to know how to select a certain aperture, but it is more important to know when to use one aperture rather than another one.

Robert de Niro, by Steve McCurry

Robert de Niro, by Steve McCurry

My answer: Yes and no. As with all things, it depends.

This is not my photo, of course. I wish I was Steve McCurry and could get to take a portrait of Robert De Niro. Maybe one day.

Steve McCurry is a master and masters don’t do anything at random. He knew exactly how he wanted this picture to look. He probably envisioned this picture weeks or months in advance.

He wanted to make what is called a contextual portrait: a portrait of someone in a meaningful context. In this case, the context is a movie theater. We can easily see it, but it’s not so sharp that it takes attention away from the main subject, Robert De Niro.

It is also not so blurry that it becomes an indefinite wash and we are left with a portrait that has no context at all.

I don’t know what aperture McCurry used for this portrait, but I can tell you that it was not f/22 (too much DoF) and not f/1.4 (too little DoF). Indeed, if you watch this video there is some behind-the-scenes footage of this shoot and, at some point, you can hear McCurry say: “And then I’m gonna try one at 4.” obviously meaning f/4.

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