Nex-7 vs EM5 Shutter Speed comparision at ISO 200

Started Apr 3, 2013 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: Nex-7 vs EM5 Shutter Speed comparision at ISO 200

KenBalbari wrote:

I'm curious.  In these kind of threads trying to sort out what always seem to be fairly small differences (say 1/3 a stop) in reported ISO, there always seems to be an unstated assumption that reported shutter speeds are accurate.  Is there any technical merit to that assumption? Do we know that shutter speeds are accurate to within 1/3 stop, any moreso than ISO?

I especially wonder since fine adjustments on shutter speed are normally not possible.  You typically can't set a shutter of 1/36 for example.  There may be no intermediate steps at all between 1/30 and 1/40. Doesn't mean those aren't accurate.  But if the speed were 1/38 for example, the camera software might not even allow that to be reported.  That might have to be reported as 1/40.

In addition to the question of how accurate the shutter is when manually set to a specific value, there is an additional question that merits attention in this context, namely how the reported shutter speed matches the one actually used. It is pretty well known that in aperture-priority mode, the reported shutter speed can be as much as 1/6 EV off from the continuously variable shutter speed (no restriction to steps of 1/3 EV in this case) that the camera actually uses. It follows that two cameras can actually use virtually identical shutter speeds and still be 1/3 EV apart in terms of reported shutter speeds.

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