What the Hell is Depth of Field?!

Depth of field is a concept often spoken about in photography circles and articles.

There are those laconic comments of “check your depth of field” and “I love how you managed your depth of field.”

But at some point you ask yourself “what the hell is depth of field anyway?” 

People always assume that you know what it means even when you start out in photography.

I studied photography a little in Secondary School but depth of field never came up! It was an art class which used photography and the darkroom as a medium for art, rather than a guide to the technical aspects of photography.

Most of us had some cheap old cameras that we barely knew how to use! So some of the details of photography fell through the cracks. Depth of field was one of them. 

Because I loved playing with my camera, eventually I started to read photography books but I tended to skip the boring stuff and try to find out how they made certain images and how I could make them as well!

So when I made a friend who was older than me and had a lot of experience in photography, it was great to finally have someone to talk to about this stuff!

My friend, Peter Greenstreet (you can check out some of his work here), for a long time specialised in macro photography, with some stunning pictures of dragonflies taken here in the UK 

In conversations with Peter he would mention technical details that I had overlooked, which would then force me to look them up so I could understand what the hell he was talking about! Depth of field was one of those terms. But I struggled with the explanation I found. I just didn’t quite get it.

So I asked Peter, and he explained it how he learnt it and it made sense. But, this was one of those ideas that just would not stick in my brain and it flew straight out of my ear. 

It took me a few years to get the concept stuck in there and for me to actively think about my depth of field when I am shooting an image. Every time I read it in a magazine article or photography book or online, even when it came up in conversation with Peter, I would be looking quizzical and have to ask “what was that again?” 

In truth it is not that complicated but I struggled to connect the idea of it with its name. Why was it called depth of field? To be honest I’m still not sure. I would have called it field of focus personally but that will become apparent when I explain what the hell is Depth of Field!

Time to get Technical - Focus Points

Depth of field is related to your focus point and aperture. In modern DSLR cameras there are many different points in your viewfinder that can be used to auto focus your lens and view. A lot of the pro photographers choose a single point to focus on.

The point that above all else in the image needs to be in focus.

In portrait photography (and wildlife) that point is the eye. If the eye is not in focus then the image is not going to be that good (in general!). 

My Canon 5D mark III, for example, has 61 focus points and the possibility to have a selection of them or a single one in use. I often choose a single point, to try and limit the autofocus searching for something that I don’t want in focus to be in focus. Instead I can simply position the single point on the exact thing that I want in focus and let the autofocus take care of everything else. 

Your focus point is determined by your distance from the subject as well.

In landscape photography you are often shooting at infinity point focus. In other words you are so far away from the subject that your focus point is always in focus. Whereas being closer to the subject means your focus point has to determine your exact distance from the subject.

Your distance from the subject determines your depth of field, more on that below.

Back to Basics - Aperture

Aperture, for those that don’t know, is the size of hole at the end of the lens that connects to the camera. It determines how much light hits the sensor (or if you’re old school: film).

You or the camera can control the size of the opening.

The confusing part is that the lower the number the bigger or wider the opening, so f/2.8 means that aperture is really large and lets in a lot of light, whereas f/22 means the aperture is really small and lets in less light. 

This is why aperture determines your shutter speed. A big opening means a lot of light, which means a very quick shutter is all that’s needed to get an image.

Whereas a small opening means a small amount of light, which means it takes longer to get an image. 

The Relationship - Aperture and Focus Point

Depth of field is the relationship between those two factors: your aperture and focus point. With your focus point you have determined what has to be in focus, now your aperture can help you to pick what else is in focus. Your aperture will determine what is in focus further away or closer to your focus point.

A wide aperture like f/2.8 means that you have a shallow depth of field. This means that it is a very small distance either side of your focus point that is in focus and the rest of the background or foreground will be blurry and out of focus. (Macro photographers love this!)

A small aperture like f/22 means that you have a large depth of field. This means that it is a large distance either side of your focus point that is in focus, so your background and foreground will both be sharp and in focus. (Landscape photographers love this!) 

So a way of thinking about this is that: IF you want everything in focus then use a closed aperture like f/11 to f/22; BUT IF you want only one area in focus and the rest blurry and out of focus use a wide aperture like f/2.8 to f/8. 

The area that is in focus is your depth of field. Where you place your focus point and the size of aperture you choose will determine how much depth of field you will have. However, the other key factor that determines your depth of field is your distance from the subject. 

Put it all together - Focus Point, Distance and Aperture

The focus point is the middle point of your depth of field, the area surrounding it that is in focus is your depth of field, which is determined by your aperture.

If you are standing really close to a subject with a wide aperture (f/2.8) then your image will have a shallower depth of field than if you are standing really far away from your subject with the same aperture.

That’s because your focus point has a larger area naturally in focus when you are standing far away. So being farther away also increases your depth of field regardless of your aperture. In other words, the closer you are the more blurry the surroundings, the farther away the more that is in focus. 

When you are using an aperture of f/2.8 and you are a few centimeters away from your subject, your depth of field is shallow: only a few millimeters, meaning that the majority of the image will be out of focus.

On the other hand, when you are  using an aperture of f/2.8 and are 500 meters away from your subject, your depth of field is larger: a few meters, meaning that a large portion of the image will be in focus. 

So when you are using an aperture of f/22 and you are a few centimeters away from your subject, your depth of field is large: a few centimeters, meaning that the majority of the image will be in focus.

Moreover, when you are using an aperture of f/22 and are 500 meters away from your subject, your depth of field is massive, and the whole image should be in focus.

Quick Tip

On most cameras there will be a button to show you what your depth of field will look like in your view finder. On Canon cameras it is a button to the left of the lens, as you look at the front of the camera, just below the shutter button. It basically closes the aperture for you to show you what your depth of field will look like. 

Conclusion

Depth of field can be a useful artistic tool to choose specific areas that are in or out of focus. I hope you can see why I think it should be called the field of focus rather than depth of field, as it is literally what is in focus.

Your focus point determines what has to be in focus and your aperture determines what surrounding that point is in focus and both are reliant upon your distance from the subject.

The closer to a subject you are means that the area that is in focus is smaller than if you are further away.

Your aperture helps to determine the size of area that is in focus.

If you want a large area out of focus then you need to be close to your subject with a wide aperture.

If you want everything in focus then you need to be far away from your subject with a closed aperture.

The area that is in focus is your depth of field, which I hope you now have an understanding of and can control for yourself. 

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Written by Daniel Long

Daniel Long created DRL Photography as a place to showcase his work as a photographer. Daniel has learnt a lot about photography and wishes to impart this knowledge with you, although the world is an ever changing place and he always says “you can never learn everything.” So as he makes his way, he continues to learn knew techniques, skills and information about photography. He focuses on Landscape and Wildlife photography and Daniel has a special focus on Scotland, his home away from home. As well as writing about photography and taking pictures out in the field, Daniel offers guided photography days so he can share his knowledge and locations in an effort to give his clients the best opportunities possible. Have a browse around this website to see his images, guided experiences and articles about photography. If you have any questions don’t hesitate to get in contact.