Thursday, November 4, 2010

Digital Photography- Depth Of Field and Aperture

This entry refers to what is possibly my favorite tech gadget- my Fujifilm Finepix S-700. After the loss of my first digital camera in late 2008, I finally entered Wal-Mart about a year ago to purchase a cheapy point-and-shoot little box I could slip into a shirt pocket for impromptu snaps. My budget was $100 or less. The plan was to later purchase a much better camera after saving for it. But, I happened upon this one and was impressed with the features it packed at such a modest price. I could see immediately it was an older model but I still liked it. It was about $130 so I revised my budget upward on the spot and bought it.

Depth of Field describes the range in a photo which is in good focus. The more narrow aperture used, the greater the depth of field. The wider the aperture, the less the depth of field. The tradeoff is that a narrow aperture limits the amount of light allowed in, thus darkening the image.

Here's a good description of the depth of field concept at Wikipedia:

Depth of Field

The aperture is the hole through which light is shined upon a piece of film (in a conventional camera) or the sensor (in a digital camera). The camera can automatically set this as it sees fit to get proper exposure, and many digital cameras let you adjust this for different effects. I put my camera to its absolute narrowest setting for a wider range of clearly focused objects in the image.

Here's a good description of the aperture concept at Wikipedia:


Cameras use a contrary numbering system for designating aperture settings, thus 3.5 is the widest my camera supports, and 13.5 is the narrowest.

Note in picture 1 (settings: f 13.5, 1/10s, ISO 100) the range of clearly focused objects as indicated by the arrows. I used the narrowest aperture and the range of focused objects is pretty wide:

Note in picture 2 (settings: f 3.5, 1/32s, ISO 100) I did the opposite and put the camera to its widest aperture setting to lessen this focusing range. Note the placement of the arrows and the much smaller range of focus. Also note how much brighter the second image is; this is another effect of a wide aperture:

Note that I used this camera's macro mode for photographing small objects very close to the camera. This mode limits depth of field very much to begin with, and I narrowed it further with a wide aperture.

Some folks use a narrow aperture to make sure all objects in the frame are in focus, and some use a wide aperture to keep only one item in focus, to emphasize that object. You might want to highlight a person's face this way. I tend not to shoot this way; I usually adjust shutter speed and aperture to get good exposure. If I had to choose I would adjust for a more narrow aperture so everything is in focus. This is probably because I shoot scenes and landscapes frequently, where there is no subject and anything in the frame could be of interest.

This is relevant because, if you are curious, at some point you may want to switch your digital camera from Auto to Manual and make the photography decisions yourself.