Dissapointing Sony A77 II High ISO performance

Started May 2, 2014 | Discussions thread
TrojMacReady Veteran Member • Posts: 8,729
There are no apologies needed

fishywisht wrote:

TrojMacReady wrote:

People have removed their mirrors and compared image brightness: about 0.5 EV difference (compensation required in a converter to equal brightness). The actual transmission values of the A77 mirror/beamsplitter (without camera) have been measured in a lab at different angles. At the angle used, that turned out to be 70 to 80%. The former translates to 0.5 EV light "loss" and corresponds with values mentioned in the various Sony patents.

As for AF comment, that makes no sense whatsoever. The AF and metering sensors in classic DSLR designs also get about a third of the light (through the semi silvered center of the main mirror, bounced via a small secondary mirror behind it) while the rest is reflected to the OVF. Meaning, those AF sensors have to work with only a smaller portion of the light too.

The A77 understates ISO's, a few competitors overstate ISO's, that alone leads to wrong conclusions about signal to noise ratios of these cameras and the effect of the beamsplitter (between 0.3 and 0.5 EV as described above).

Good info, except the apologism for the A77 noise. Why anyone tries to argue is sad, because it stands out so badly and is why I never even shortlisted it.

No apologies, just verifiable facts. At the same ISO, a Canon 7D requires up to 2/3 EV slower shutterspeeds. Fujifim cameras and the EM5 overstate even more. The only sensible comparisons compare at the same physical exposure settings (shutterspeed and f stop) and then equalize brightness differences afterwards. That takes ISO ratng differences out of the equation.

On the dpreview comparator the A77 noise at 3200 is worse than the D7100 by easily 1+1/3 stop- for instance the D7100 @6400 is clearly better on the flesh tones where a lot peer at it. Arguments about the exposure being more or less generous fall to the exposure values in the files for download which nowhere near makes up the difference. Maybe Nikon was right to hold off from the 24MP DX for 18 months compared to Sony.


See above, add the fact that the D7100 has a newer generation sensor (approx. 1/3 EV more effiient), add half a stop for the beamsplitter and it suddenly makes a lot more sense. Real difference at the same physical exposure is closer to 2/3 EV.

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