Depth of Field is an important concept to understand in helping you control image composition when taking any photograph, and this is important with macro photography too.
In this article I will be looking to show you how Depth of Field (DOF), effects your image.
With macro photography, particularly when focusing up close and personal on a subject at 1:1 or greater magnification, your depth of field will reduce down even at the highest F rating of your lens to millimeters, and even less when wide open (a low F number eg F2.8). To this extent it is worth realizing how you can preview this in the field (if you camera has a DOF preview button it can be handy to use, though at the higher F ratings this will likely make the image very dark). Some more modern digital camera may allow you to do this via their “live view” screens.
If you have a digital camera you can of course view the captured image in the LCD screen after taking. As you become more experienced you may well find you can visualize mentally this effect before pressing the shutter button / previewing the image. Anyway I digress.
By shooting at your highest F number for the lens (eg F16) – called oppositely (or confusingly maybe) a low F rating, this will allow you to bring as much as you can into focus of the subject and background. This may be useful if you wish to put more of the subject in focus, or you want to show the background. However it may also mean that some of the items in focus distract from your image (eg messy leaves, twigs in background). Below is an example of a shot of a fly taken at F16.
It maybe that you’d prefer not to have so much of the image in focus or maybe you need to use a lower F number to get a reasonable shutter speed to take the shot (as the higher the F number the less light the lens is letting in over the same amount of time as a lower F number, so to get the same exposure you’ll need to take a longer time). This image of the same fly is taken at a lower F number (F10).
Lastly maybe you really want to isolate the subject or part of it/blur the background. Then you may consider using your lens wide open or near to it’s lowest F number. I did this in the photo (F5.0) of the fly to draw the attention to it’s head, by making this the only part in focus of the subject.