Subject:	I don't buy it
Author:	drdread
Date:	4/14/2002 8:33:06 PM
Message:

The 'shutter lag' has to have something to do with prepping the CCD. The two sources of delay you mention can't account for it. To wit: light collection has to be a short-duration event, or shutter speeds like 1/60 would be misleading and/or meaningless. Think about what happens: you press the button, a full second elapses (or whatever the actual delay is) and then it opens the shutter (virtual or physical -- it's irrelevant), and then 1/60 or 1/125 seconds later, the shutter closes and CCD readout begins.

A post-acquisition delay (i.e. readout, JPEG conversion, write to permanent storage) is just that: post acquisition. That delay would affect your frame-to-frame delay (i.e. frames-per-second rate) but not the interval between "press the button" and "capture light."

So whatever the source of the delay is, it has to be something that they're waiting to do until the button gets pressed. Perhaps it's something as simple as clearing the CCD of previous image data. I can see how cheaper cameras would forego a physical curtain for lower construction costs, which would mean the CCD is exposed to light constantly...you'd leave the thing in an idle state until the button gets pressed, then clear it, then start an acquisition cycle. Maybe that's the source of the problem.

I know very little about this particular subject, so this is all conjecture on my part. But I do know that the high-end machines (Canon 1D, Nikon D1x, etc.) don't have this problem. They quote shutter lags in the same vicinity as old-fashioned SLRs. Probably the exact same numbers, actually, as they really *are* old-fashioned SLRs except for the photosensitive parts. :)

Anyone have definitive info on this subject? I'm going to start searching right now.

D

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