depth of field

Babzy referred to the increased 'blurriness' in some of the pictures I've been taking with my new lens. Depth of field is, technically, directly related to the size of the aperture opening. The wider the aperture opening, the less time it takes for enough light to hit the film or panel for a picture to be taken. If a picture is taken with the aperture wide open, there is less time for the image to burn, and the result is a shortened depth of field. When a picture is taken and everything is the foreground is in focus the same amount as the stuff way in the background, it means the aperture is set to 'infinity' and everything will be 'in focus.' Point and shoot cameras are focused at infinity.

Below are 4 sets of pictures to give you a visual reference.

In this set, the first one was taken at f1.4 and the second at f2.0. You can clearly see how much more of the picture is "in focus." Although there are a multitude of creative reasons for wanting to use a wide aperture/narrow depth of field, on a technical level one of the best up sides of a wide aperture (small f-stop) is that you can take a picture faster, with less available light. The down side using this technique is that you have to be very conscious of where the focal plane or 'sweet spot' is, which requires some practice, especially if you are shooting moving objects.


The dirty little secret on depth-of-field is that if all you've got is a point-and-shoot digital, you can ~sort of~ create the illusion of depth of field with even the most basic of photo editing software using what they usually call the 'soft focus,' a feature that allows you to select a portion of the picture to be kept in focus while the rest of it has a filter applied to give it a blur. The second two pictures illustrate the before and after of applying soft focus using Picasa, a free download you can find here.

If you are going to use digital photo editing to mess with your point-and-shoot pictures for things like depth of field, it's a good idea to experiment with the angles you shoot so that when you apply the filter you get the most 'realistic' effect. The next pictures here demonstrate what I would consider a 'bad' Picasa edit job on a point-and-shoot image. The one above is sort of taken from the top, and your brain would expect it to be blurrier down the column, whereas a picture taken from the side like this, your brain knows that unless your lens had a fingerprint on it, there's no reason for just the top of the cake to be in focus. Be conscious of the plane you are shooting from, and you will have no problems.


This last set further illustrates depth-of-field employed strictly for creative purposes by showing the same pile of sand dollars photographed from different planes using my digital SLR camera with my beloved new lens.