Sunday, 29 April 2012

The Macro Depth of Field Challenge!

A nice example of the challenge of depth of field in macro photography. With a large aperture (small f number) f5.3 in this case, and near the minimum closest focus distance (maximum magnification) for the lens, there is virtually no depth of field, especially with large focal length lenses (300mm equivalent in this case). On this close-up of a Green Shieldbug the compound eye is in focus, together with a fine line along the length of the body, but everything nearer or further away is blurred. Click on the photos to see this more clearly...

To increase the depth of field with any lens use a smaller aperture (larger f number) or back away from the subject a bit (the image gets smaller though). If you use a smaller aperture then the exposure time must go up, increasing the risk of camera shake, and hence the need to use a tripod. To counter this you can increase the ISO number (equivalent to film speed in the good old days) but then the noise will increase leading to loss of detail. The lens' ability to resolve detail may also decrease with small apertures.

Macro photography is thus a wonderful balancing act of parameters. It is also a physical balancing act - trying to hold the camera steady, usually in an uncomfortable position, whilst holding your breath to prevent movement and wobbling back and forth to get the focal point just right! It's no wonder that the keep-rate for macro pictures is so low!

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