how does Sony get SLT to expose "normally"?

Started Sep 13, 2012 | Discussions thread
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William Porter
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how does Sony get SLT to expose "normally"?
Sep 13, 2012

Sorry, Google isn't helping me here, and what Google does find, well, some of it looks unreliable.

I've done a number of tests with my A580 and my A77 side by side, checking for differences in exposure. There aren't any, or if there are, they're very slight. If the A580's meter thinks the right settings are ISO 800, f/3.2 and 1/30 sec, the A77's meter will think the same thing. This is really important, because if this weren't the case, then my handheld light meter wouldn't work reliably with the A77.

But how does Sony make this happen? After all, less light is getting to the A77's sensor than to the A580's — about 30% less, according to Sony. Other things being equal, the A580 thinks f/3.2 is the right aperture, I'd expect the A77 to ask for f/2.8.

I can think of two things that might explain what's happening.

My best guess is that the sensor in the DSLT has been enhanced or goosed a bit so that it's more sensitive, so that (say) ISO 800 on the A77 roughly = ISO 1000 on a DSLR like the A580. This would also account for the slightly noisier output of the DSLT.

Another possibility is that the meter on the DSLT has been biased a little downwards , so that a nominally correct exposure on the A77 will be slightly darker than a nominally correct exposure of the same scene on an A580.

Or both.

Anybody actually know ? Is it one or the other or both, or something else altogether? A link to something authoritative would be fantastic.

Thanks,

Will

 William Porter's gear list:William Porter's gear list
Panasonic Lumix DMC-LX7 Olympus E-M1 Panasonic Lumix G 14mm F2.5 ASPH Olympus M.Zuiko Digital ED 40-150mm 1:4-5.6 R Olympus M.Zuiko Digital 45mm 1:1.8 +7 more
Sony SLT-A58 Sony SLT-A77
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