Friday, November 13, 2009

Rethinking DOF


For my 7D, I’m recalibrating myself when setting the aperture. One of the complaints – or benefits – of my G9 was the extreme depth of field that was in focus. In fact, getting a blurred background was a challenge when using the G9. Further, because the sweet spot for the G9 was around f4, my choice was usually f4 or so. After two years of primarily using the G9, this choice became habitual.

For the same f-stop, the depth of field with the 7D is considerably less than the G9. For this shot, I was using the 7D with 15-85mm lens set at 70mm and f8. This image was down sampled from the in-camera JPEG. From roughly six feet away, the depth of field is only about seven inches. I focused on the face but clearly the hand is not in focus even in this downsized image. With my G9 at f8, the depth of field (for the same image size) would have been about 22 inches. Even with my G9 at f4, the depth of field would have been about 10 inches.

I’m not particularly bothered by the hand being out of focus here; in fact, that’s OK. I do wish the little bird were a little better focused though. The slightly upward and left-right angle of this shot puts the bird at the edge of focus and a bit soft. I should have shot this one at f11 or even f16 and focused more towards the beard. The depth of field at f16 would have been (coincidentally) 16 inches.

I knew to use higher f-stop numbers with the 7D but habits are hard to break.

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