Depth Of Field For Dummies

I'm a bit thick when it comes to explaining the technical side of Depth Of Field but I'm going to give it a go anyway...

Depth of Field (DOF) is an element of photography that amateur camcorder users rarely consider. It's a shame considering that as setting the DOF correctly on a camcorder for each shot can drastically alter the tone and feel of the footage.

DOF is the area within your image that a subject could freely move about whilst remaining in focus. If you were to imagine a football game and you were standing by the net of one team looking across the pitch at all the players spread around, if all the players were in focus then this would be a very large Depth Of Field. Taking the opposite approach, if you were still standing in the same position but only the players within 20-30 feet of you were in focus then you would have a smaller/shallower DOF.

DOF is determined by three factors: The distance at which the subject is in relation to the camera lens, the lens aperture/iris and the lens angle.

Subject Distance

Whatever you might be filming, be it the local wildlife, your child's first steps or even the neighbours dog taking a dump on the driveway, the distance at which the subject is from the camera affects DOF. If your subject is very close to the camera then you will instantly have a shallow/small depth of field because your camcorder can't see anything else. However, the further away the subject is the wider the depth of field will be and the more things that will come into focus depending on the status of the two other elements of DOF.

Lens Aperture/Iris

Not all camcorders allow you to manually control the aperture/iris but the better ones do. The more light you allow into the camera through the iris, the shallower the depth of field you will have and likewise the opposite is true. The light reaching the camera through the iris is measured in F-Stops such as F1.4, F2.0, F2.8, F4.0 etc. The bigger the number, the less light that is getting through the iris.

Big, fast sporting events would be filmed with a larger F-stop to allow less light in through the iris ensuring much of your shot remains in focus (large DOF). It's get's a tad confusing doesn't it and I'm leaving out most the technical crap!

Lens Angle

The lens angle or focal length is the amount of information your camcorder can see. Most people have heard of a wide-angle lens and the effect it will have on an image. They are ideal for large, panoramic vistas or for small, confined spaces where you need to cram more stuff into your image without moving your camcorder back. Depending on the angle at which your own camcorder lens is set, this will effect the DOF. The larger and wider the angle, the larger the DOF. The narrower your lens angle, the shallower DOF.

So why not just have a large DOF and be done with the focus knob?

You could do this and probably would do this if you were filming a sporting event or such. However, for the true artist DOF will be far more important. Setting it correctly will allow you to ensure that your subject is the centre of attention rather than some ghastly background or foreground object hogging the limelight. Take these three pictures for example (which I stole from this site)

	Shallow DOF Notice the wine glass is nicely in focus but everything else is blurry. The booze looks mighty tempting.
	Shallow DOF Still a relatively shallow Depth of Field but the wine bottle is the focus of our attention. Both background and foreground are out of focus.
	Large DOF For this shot, most objects are in focus (steadily going out of focus towards the wall at the back). Glass, cork and bottle are all in focus (although not razor sharp). This shot probably explains DOF the best as you can imagine if you moved any object around it would still be in focus whereas if you did it in the above two shots, your subject will quickly lose focus.

Picking A Setting

It really is down to you, the Director, Cinematographer, Director of Photography or whatever you want to call yourself as to what DOF to have for each shot. Just remember, your subject should really be the only thing in focus to avoid it getting lost with everything else in shot.

Hollywood movies have that dreamy-look about them and it is partly down to DOF. Take a look at any mainstream movie, in any scene you will find nicely focused subjects and blurry everything else. This way the audience never takes their eyes off what YOU want them to see. If you don't set the DOF correctly, eyes may begin to wander around.

Please consider this guide as only an introduction to DOF with the basics that you need. If you need more info, please see below but warning, these sites may blow your head off with info!

Additional Reading