Accurately comparing FF vs APS-C sensor performance? An open discussion.

Started Apr 8, 2013 | Discussions thread
VirtualMirage
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Re: Accurately comparing FF vs APS-C sensor performance? An open discussion.
In reply to Wally626, Apr 10, 2013

Wally626 wrote:

The average difference for the A77 from your numbers is 0.29 stops and the A99 0.81 stops. This 1/2 stop difference is about the same amount the DXO ISO ratings for the A99 are below what would be expected for the sensor.

Has anyone verified this is real life conditions with the A99. For instance use an incident meter to calculate an exposure for a scene and use those numbers to take the image. I would really be suprised if in real life the A99 was missing the exposure by .8 stops.

I did a quick and dirty check with my A77 and it was off about 0.3 stops which would be inline with your numbers above.

Do you shoot RAW or JPEG?

So knowing this, do you now permanently set your A77 with an exposure compensation of .3 stops or do you leave it alone and adjust in post?

I don't have an A99, but I do have an A77 along with a Sekonic light meter and a ColorCheckr chart that has a gray scale flipside.  When I get a chance, I am going to measure mine as well using my Paul C. Buff Einstein E640 strobe as the light source.  That way I can test it across the ISO range and at different apertures to see if what I get matches the DXOMark measurements.

But I have to keep in mind the potential offset due to the light transmittance of the lens as well.  Looking at some of my lenses on DXOMark, I see light transmittance variances ranging from very little difference than advertised to as much as .1-.3 Tstops difference.  While the camera will compensate for this when not in M mode, the light meter measurement would not unless you know of the Tstop variance to begin with when working with studio strobes.  This can cause a slight over/under exposure which is easily fixed in post, but might throw off what we are testing for.

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Paul

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