DOF at its best! Questions.......

AMOMENT · Oct 9, 2011

I have a question about DOF. I understand the concept of it and how aperture/focal length/position of yourself in relation to the subject all factors in. However, I do not understand how to calculate my DOF. I know there are calculators for this which is all well and good except for that once the numbers are calculated I'm not really sure how to interpret them. What is exactly a good DEP number or bad? I know there really is no "bad" number but perhaps someone can give me an example of how specific DOF calculations would present itself in a given photo. I mostly photograph people. They are usually natural and not posed shots and alot of times are of children who are constantly changing posititions. I tend not to do action pics so I rarely use shutter priority. For some reason I do not get the quality of picture that I like using that priority.
Any suggestions for how to shoot and calculate DOF when your subject is not in a constant location? I currently have the Nikon d3100 and the 18-55 mm f-stop 4.8 lens that it came with as well as a 50mm f/ 1.8. What type of lens should I be looking to get if I plan on adding to my collection but still photographing the same genre? Thanks!

cgipson1 · Oct 9, 2011

Try this... pretty self explanatory.... if you need more, ask...

Online Depth of Field Calculator

Derrel · Oct 9, 2011

I am assuming you want shallow DOF shots, with the kids in good focus, and then the backgrounds defocused. Without going into a lot of detail, I would say that what you are looking for are wide-aperture lenses, also referred to as "fast-aperture" lenses. The easiest way to calculate Depth of Field is to use a camera that has a depth of field preview button, and to press the button, and to visually "see" what the background looks like. That takes about 1/5 of a second to do. ANother fast way is to use lenses that have DOF scales engraved on the lens barrel, on a camera with the appropriate capture format for the lens design, meaning FX format on MOST Nikon lenses. Most DX Nikkors have no DOF scale, or a very skimpy, useless one. The third method, which takes about 3-4 seconds is to actually shoot an image, and then review it on the camera's LCD. THe last of the three methods is probably the easiest for the new photographer to use, and it works pretty well.

The problem is focusing errors, and inadequate Depth of Field can easily ruin a photo, especially if it has 2 or 3 kids in it; at even slightly different distances, with focal lengths in the 50-100mm range, if the lens is set to a wide aperture like f/2.8, at closer distances of let's say 15 feet or closer, DOF is very skimpy. There really is no "DEP number", as you referred to it....I'm not sure what you meant by DEP number.

I have done a fair bit of candid kid photography, and I would say the way to approach it is to pick an f/stop that will give "some" depth of field....not the most-extreme amount, so stay away from using f/numbers like f/11 or f/16 unless you WANT to have deep DOF that extends far behind the kids. With the 18-55 kit zoom, a good "safe" f/stop would be f/5.6. THat usually gives a pretty good shutter speed, across most lighting levels. In the evenings, when the light level is LOWER, you WILL need to elevate the ISO value to 640 or 800 however, or put up with blurred movement on the kids' hands and legs and whatever is moving. As you have found, Shutter priority is fairly useless for family photography, unless you are doing slow-speed panning shots, where you really WANT a SPECIFIC SPEED to make motion effects appear "just so". LIke, for example, a kid pulling a red wagon--try panning in shutter priority at 1/5 second....it looks just about right most of the time, from a side-view and 10-20 feet away. If you wish to show a child's hair blowing in the wind, and have a tripod or VR lens, Shutter priority at say 1/15 or 1/8 second can be good.