Tag Archives: depth of field

Be sharp: learning about Depth of Field

Depth of Field (DoF) is one of those terms you see bandied about in photographic circles—a bit like bokeh—but it’s usually assumed you already know what it is and how to do it.

Put in the simplest terms, depth of field is how much of an image is in sharp or nearly sharp focus from your camera’s imaging sensor (or film) to the horizon. There’s plenty of discussion, including useful links and a series of hideously complex-looking tables that help you calculate DoF at the

Dofmaster.com web site. If you’re lucky enough to own a PDA or even one of those shiny Apple iGadgets, then there are also useful downloadable bits of software that will do all the complicated stuff for you. But, I digress—something I tend to do a lot…

Rather than go into all the technical stuff about focal lengths and circles of confusion, which Dofmaster does with alacrity and far, far better than I ever can, I shall concentrate on the practical use of DoF in model photography. As you will see, I take a more laid-back attitude to working it all out, but first, a quick resumé of why DoF is important in this sphere of photography.

The chief aim in taking photos of models is to fool the viewer into believing they are looking at a picture of the real thing. We achieve this by setting the camera at the right angle, and by ensuring that as much of the image as possible is in sharp focus.

Here, then, in a nutshell, is the technique I use to take a photo:

  • Set the camera to Aperture Priority (Av) mode, and switch focusing to manual. Yes, you can use it in full manual mode, but let’s just say I’m happy to let the camera’s sophisticated electronics work out the exposure for me.
  • Get the camera as low down as possible, preferably on a sturdy tripod, in relation to the subject. Remember, we’re aiming for a view that looks as if you’re holding the camera to your eye at head height if you were in the real world, say about 1.6m above the deck.
  • Frame the shot, and manually focus about a third of the way along the subject. It’s also useful to check the nearest and furthest points of the subject will be in focus at this stage.
  • Set the camera’s aperture to ƒ/22, or higher if the lens will do it.
  • Press the aperture preview button (check your camera’s user manual to find it) and have a good squint through the viewfinder to see if it sort of looks like it might actually be in focus where you expect it to be.
  • Nearly forgot to connect the remote release cable! This is important so you aren’t likely to jog the camera when you press the shutter button. You can set the camera to timed release, where you press the shutter and there is a countdown of several seconds before the shutter fires, but the remote cable looks more professional! Camera shake is not much of an issue with shutter speeds of 1/100th of a second or higher, but very likely to be a problem with the shutter open for several seconds – which it most likely will be.
  • Once you’re happy that all is set, stand away from the camera and tripod, and fire the shutter. Depending on how long the exposure turns out to be, make light conversation with those around you, or go for a long lunch. Do not be tempted to move the camera until you hear the shutter close again, or the new image is displayed on the camera screen.

With DSLRs, you can see a preview on the back of the camera, so you have a fair idea if the shot worked or not. This, however, is really only good enough for exposure, so focus checking has to wait for viewing on your computer later.

When I can, I like to take my MacBook Pro with me on a shoot, and tether the camera via USB so the download occurs as soon as the image is being dumped to the CF card. This allows me to view the new shot very quickly to assess for lens flare, straightness and, of course, DoF.

I’ve cooked up some samples to show how changing the aperture changes the depth of the sharply focused area. I apologise they’re not particularly photogenic model shots, but I wanted something reasonably extreme to demonstrate how DoF works. I’ve also thrown in a couple of zoom shots to show why such lenses are not ideal for this kind of work. Remember, several posts back, I said that one of the secrets is to “go wide’.

The first image is telephoto. According to the EXIF data, the focal length was 96mm, 1.6 seconds at ƒ/29. Technically, it’s not a bad photo. A lot is in focus, but it lacks a certain something. The viewpoint appears to be a long way from the subject, making the viewer feel cut off, away from the action.

The second image, on the other hand, places the viewer right in the action. This time the lens is a wide angle, 20mm focal length, with a two-second exposure at ƒ/29.

In the next post, I’ll post a sequence of photos taken from the same vantage point, but using increasingly smaller apertures.