Sony a900 vs Sony a99 II: read noise comparison

Input-referred read noise at base ISO: Sony a900 6.6 e⁻ (ISO 200), Sony a99 II 4.5 e⁻ (ISO 100).

Dual gain: Sony a900 none, Sony a99 II ISO 500.

Sony a900

The Sony a900 (DSLR-A900) was measured at 19 ISO settings from ISO 100 to ISO 6400. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (200) read noise is 1.44 DN, or 6.6 electrons at the sensor. From ISO 250 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 3200 don't change analog gain (digital push). Full well at base ISO is about 74,744 electrons; unity gain is around ISO 920.

Sony a99 II

The Sony a99 II (ILCA-99M2) was measured at 34 ISO settings from ISO 50 to ISO 102400. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 1.58 DN, or 4.5 electrons at the sensor. A second gain (dual gain) kicks in at ISO 500, cutting input-referred read noise by about 1.4 stop. From ISO 2500 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 25600 don't change analog gain (digital push). Full well at base ISO is about 44,901 electrons; unity gain is around ISO 280.

Sony a900 vs Sony a99 II read noise table

ISO	Sony a900	Sony a99 II
50	–	1.591
64	–	1.853
80	–	2.204
100	1.057	1.580
125	1.404	1.866
160	1.526	2.158
200	1.444	2.621
250	1.505	3.182
320	2.028	3.758
400	2.445	4.691
500	2.969	2.282
640	3.837	2.732
800	4.563	3.387
1000	5.502	4.056
1250	7.210	5.098
1600	9.781	6.105
2000	11.551	7.727
2500	14.825	9.514
3200	19.027	11.632
4000	22.471	14.723
5000	28.840	17.877
6400	36.758	21.706
8000	–	26.909
10000	–	32.672
12800	–	41.643
16000	–	53.446
20000	–	65.799
25600	–	82.711
32000	–	60.969
40000	–	73.517
51200	–	91.773
64000	–	112.206
80000	–	137.187
102400	–	173.645

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