a7S high ISO claim - - -over hyped or not ?

Started Jul 3, 2014 | Discussions thread
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ProfHankD Veteran Member • Posts: 4,194
Dynamic range, ISO-less sensors

TThorne wrote:

Rishi Sanyal wrote:

There's also a dynamic range benefit at higher ISOs. At base ISO, however, there's a dynamic range cost compared to the A7R.

This is devastating news to me. I am truly saddened to see this confirmed and thankful at the same time for the work you have put into it. I love everything about the A7S, but for practical issues on the job (for me at least) the A7 and A7R seem like the reigning champions, as I value low ISO DR above much else.

I don't know why people expect cameras with good very high ISO performance to do well at low ISOs -- that's really not how it works. The DR for the A7S at higher ISOs appears to be significantly better than any other camera DxO has tested, and 13+ Evs at low ISOs is pretty amazing for the same sensor. Makes one wonder where they put all that charge....

More specifically, there's been a lot of discussion in the past about sensors being ISO-less: underexposing at a low ISO and digitally adjusting the raw does as well as turning-up the analog gain (ISO setting). In fact, last year I had students do a little project that confirmed even some cheap Canon PowerShots using CHDK are essentially ISO-less. Most Sony sensors seem to be ISO-less, which is what you'd expect if you have good analog signal handling. Anyway, the point is that the A7S clearly is not ISO-less. Perhaps sensor DR really is that 15+ range Sony mentions (without citation) and the analog electronics just are not able to cover it all without a gain adjustment?

Personally, I miss ISO 25 because that's what I was most often shooting at with film (Panatomic-X in 1:100 Rodinal or Kodachrome 25). I know you can (usually) use an ND filter to get the same effect, but adding filters isn't ideal....  And yes: I would use ISO 25 more often than ISO 100K.

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