SLT camera light loss - A99/A7 comparison

Started May 31, 2014 | Discussions thread
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SLT camera light loss - A99/A7 comparison
May 31, 2014

To determine the amount of light lost to the translucent mirror in Sony LST cameras I made this comparison:

I shot the same scene with a Sony A99, and an A7.

Both cameras were set to 1/30 f:8, and fitted with a Tamron 28-75mm/2.8, on the A7 it was mounted via the LA-EA4 adapter with a built-in mirror/af system. Both cameras set to auto ISO.

Below crops from the centers of both images, the top one from the A7, then the A99. Both files are JPEGs exported from RAW in Lightroom, with the default settings of sharpness 25/rad.1, luminance n.r. 0, chroma n.r. 25:

Interestingly, both pictures were exposed virtually the same, according to the histograms. However, the one from the A7 was exposed at 4000ISO, whereas the A99 was 3200. Looking at the noise patterns from these apparently identical sensors they seem, to my eyes at least, to be very much the same. This seems to indicate that the A99 uses the same signal amplification at 3200ISO as the A7 at 4000, to compensate for a light loss of about 1/3 EV - the same amount by which the A7 increases the ISO compared to the A99 because of the mirror in the adapter.

I hope this can help those who worry about the amount of light lost to the mirror in the SLTs.

Sony Alpha 7 Sony SLT-A99
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