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DEP

Canon's Little-Understood
Depth-of-Field Exposure Mode
and How to Use it Effectively

High-end Canon SLRs — film-based as well as digital — feature a mode called DEP. (This includes the 1V, Elan 7, EOS-3, 1D and 1Ds. See the section on A-DEP below for more on other Canon cameras). This is short for Depth of Field. It permits you to have the camera automatically select the hyperfocal distance and appropriate aperture for that shot, so that the nearest and farthest objects in the scene are both in focus.

It used to be (back in the early Paleozoic — until about 1985) that lenses had depth of field scales. Setting the hyperfocal distance was simply a matter of focusing the lens so that the scale showed the farthest point and the nearest point desired to be within the scale of a given aperture, and then setting that aperture.

A Leica 35mm Summilux-M lens
focused at 12 feet,
showing depth of field from 6 ft to Infinity at f/11
This is what all lenses used to look like.

The advent of autofocus, and the increased popularity of zooms over prime lenses has lead to the almost total demise of DOF scales on lenses. This makes the manual setting of hyperfocal distance impossible. But Canon has a solution — the DEP mode. Here's how the manual says to use it.

— Set the camera to DEP mode

— Point at either the nearest or farthest object in the scene that you wish to be in focus and lightly press the shutter release

— Next, point the camera at the other extreme and once again half press the release.

— The camera will now autofocus the lens to the hyperfocal distance and will display the aperture that it has selected to achieve optimum depth of field

— Reframe the scene and press the shutter release to take the photograph

The factory method works well, but is not without its problems. The primary of these is that the camera may well set an aperture that is so small that the shutter speed is unusable, especially if the camera is hand-held. Since most photographers trust the camera's "automatic" modes this can lead to disappointing photographs.

Here's a better way that I have found to be appropriate for doing landscape work, especially when the camera is tripod mounted.

— Set the camera to DEP mode

— Point at either the nearest or farthest object in the scene that you wish to be in focus and lightly press the shutter release.

— Next, point the camera at the other extreme and once again half press the release

— The camera will now autofocus the lens to the hyperfocal distance and will display the aperture that it has selected to achieve optimum depth of field

These first three steps are the same as recommended by Canon. But here is where my approach differs from what Canon suggests.

— Turn off autofocus. Be careful not to touch the focus ring of the camera. Leave the focus where the camera has set it

— Make a mental note of the aperture that the camera is proposing to use and now reset the exposure mode to Manual

— If possible manually set the aperture to one stop smaller than that suggested by the camera

— Manually set the shutter speed to the setting needed for the desired exposure. If this falls outside an appropriate range for the subject that you're shooting, and you're shooting with a digital camera, reset the ISO to a higher speed.

— Reframe the shot and take it

There are several advantages to this approach. The first is that you're not under time pressure. The method suggested in the manual is for snapshots. It works, but you'll be much better off working at a slower pace. If you leave the camera alone for too long in fully automatic DEP mode it will lose its settings. Secondly, the aperture that the camera sets is for a Circle of Confusion that may not be appropriate for prints larger than about A4. If you stop down one additional stop you will find that the additional depth of field makes for a much crisper image. (If some of these concepts are unfamiliar to you you may wish to read my tutorial titled Understanding Depth of Field).

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An Example

The photograph below was taken at a focal length of 135mm. I wanted the foreground rocks as well as the distant hoodoo to be in focus. I didn't care if the mountainside in the background was a bit soft, but everything from the foreground to the hoodoo needed to be sharp.

Canon EOS 1Ds with 70-200mm f/2.8L @ 135mm

I selected a point in the lower left foreground as focus point #1 and the top of the hoodoo as point #2. (The order that you do these in doesn't matter). This produced a hyperfocal setting that needed an aperture of f/22. After switching off autofocus and changing to manual exposure mode I set the lens to f/29 to provide a bit of extra depth of field in case I wanted to be able to make a large print. Since the camera was tripod mounted and there was nothing moving in the frame I was able to leave the ISO setting at 100 and let the shutter speed fall where it wanted to.

The next time you need lots of depth of field, give DEP mode a try. Using the technique shown above can remove the guesswork from getting correct depth of field and hyperfocal settings with your Canon camera.

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A-DEP

Unfortunately not all Canon camera have the DEP function. Some do, like the 1V, Elan 7, EOS-3, 1D and 1Ds. Others, like the Rebel, D30, D60 and 10D have a mode called A-DEP.

A-DEP is a simplified mode that measures the nearest and farthest items with a single half-press of the shutter release. Unless you are able to simultaneously position the focus points on the nearest and furthest points desired (something that I find almost impossible to do), it doesn't work very well, and it definitely can't be used with the technique described above.

It would appear the A-DEP is an attempt by Canon to provide a depth of field mode easy enough for beginners to use, but regrettable by being so simple, it becomes almost useless. I'm particularly surprised to see the A-DEP mode on the D60 and 10D, cameras aimed at the more sophisticated user. Shame on Canon for this.

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This tutorial will be featured in an upcoming issue of
The Luminous Landscape Video Journal

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Concepts: Science of photography, Depth of field, Aperture, Circle of confusion, F-number, Camera, Focus, Focal length

Entities: Canon, Confusion, DEP, DEP., Michael Reichmann, SLRs

Tags: cameras, mode, aperture, hyperfocal distance, DEP mode, shutter release, farthest object, canon camera, shutter speed, autofocus, optimum depth, exposure mode, half press, hyperfocal settings, automatic dep mode, High-end Canon SLRs, manual exposure mode, shutter speed fall, appropriate aperture, photograph, digital camera, Luminous Landscape Video, nearest point, farthest point, field mode, simplified mode, DEP function, Summilux-M lens, correct depth, A-DEP mode, field scales, additional depth, total demise, extra depth, farthest items, prime lenses, manual setting, slower pace, mental note, foreground rocks