Wednesday, November 21, 2007

G9 and Closeups

A telephoto lens set at the minimum focus distance is the opposite extreme from the wide angle hyperfocal settings discussed previously. To get this picture, the G9 was set at full telephoto: 44mm (usually referred to as 210mm equivalent in terms of 35mm film). The aperture was f8 and the matching shutter speed was 1/160 sec for ISO 80 in sunlight. The G9 was about two feet away from the ring – almost, but not quite the minimum focus distance at full telephoto. In fact, I used the “macro” setting to focus on the ring.

Under these conditions, the theoretical depth of field is about ¾ inch. That is, only a distance of about ¾ inch into the picture appears to be sharply focused. The horizontal ring in the picture is about 4 inches in diameter and all of it is not in focus. Therefore, regardless of how the calculation is done, it is very obvious that the depth of field is on the order of one inch.

The G9 and similar small sensor cameras are sometimes said to be diffraction limited and those disparaging it as such will disapprove of using the f8 aperture. Don’t be afraid to use f8 – it’s OK.

Besides, at f5.6 the depth of field would only have been about ½ inch!

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