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I'm reading Understanding Exposure and ran across some discussion of apertures in fixed-lens digital cameras as compared to SLRs (page 54 in the 3rd edition). The author says that fixed-length digital cameras give much larger depth of field than SLRs, and gives some examples, but never explicitly says why the depth of field is so much greater. For example, he says that f/5.6 on a fixed-lens digital is equivalent to f/22 on a digital SLR. It's not clear to me what "equivalent" means here, but I'm pretty sure he's talking about depth of field (DOF).
I think this discussion is just saying that fixed-lens digital cameras have smaller sensors (and thus greater DoF), but I'm not sure. Can anyone help clarify or explain what the author is talking about here?