how does Sony get SLT to expose "normally"?

Started Sep 13, 2012 | Discussions thread
Dennis Forum Pro • Posts: 17,458
Re: how does Sony get SLT to expose "normally"?

After this was discovered with the A33/A55, some of us wished for Sony to implement a mode that would effectively "turn off" this under the covers ISO boost, so that in bright light situations, rather than shoot at 1/1000s at ISO 100 (that's really ISO 125 or whatever) we could shoot at 1/800s at ISO 100 that's really ISO 100.

I don't know for sure if that's what they did, but they offer a lower ISO setting on the A77 than the NEX-7 (as an example). Some cameras offer a "stretched" ISO that's below the true base ISO, but I believe that in the case of the A77, the ISO 50 setting is the true base sensitivity. If you look at the sensitivity measurements on dxomark, the measured sensitivity at ISO 100 is around 80 while the measured sensitivity at ISO 50 is around 63. This could mean that the ISO 50 setting on the a77 is the same base sensitivity you get at ISO 100 on the NEX-7, suffering a bit for the mirror. (And then the ISO 100 setting on the A77 is boosted to match what's on the NEX-7). Also, I believe that when an ISO 50 setting represents a stretched setting, dynamic range usually suffers, but on the a77, DR and all other measured attributes improve at ISO 50 (suggesting that it's a real setting).

So I think that Sony has effectively delivered a "boost-free" ISO setting by providing ISO 50 on the A77 (and any other models that offer it). Which lets good light shooters avoid the fixed mirror penalty.

  • Dennis

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