Dissapointing Sony A77 II High ISO performance

Started May 2, 2014 | Discussions thread
VirtualMirage Veteran Member • Posts: 3,956
Re: 2010 called....

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.

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.


Remember that the DPR tests are not exactly equal.  I know they don't keep the exposures the same and I can't recall if they adjust the lighting too from camera to camera.

Either way, look at the EXIF information on both cameras.  You will see that it looks like DPR is basing comparison on ISO and not on exposure values.  Knowing that ISO is really baseless on digital cameras and varies from manufacturer to manufacturer, some cameras may be understated while other overstated.

In the instance with the D7100 and the A77, D7100 has a longer exposure time than the A77 (1/1600s vs 1/2000s at ISO6400).  This gives at least a 1/3 stop advantage to the D7100.  If basing ISO on shutter speed, that would mean that if the A77 was the correct exposure and shutter speed for ISO 6400 then the D7100 would really be ISO 5000 or lower just based on that and no other possible inconsistencies in the testing methodology.  Flipped, it would mean the A77 was around ISO 8000 or higher in equivalent.

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