Sony a900 vs Sony a99: read noise comparison

Input-referred read noise at base ISO: Sony a900 6.6 e⁻ (ISO 200), Sony a99 4.3 e⁻ (ISO 100).

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

The Sony a99 (SLT-A99V) was measured at 28 ISO settings from ISO 50 to ISO 25600. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 1.31 DN, or 4.3 electrons at the sensor. From ISO 320 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 6400 don't change analog gain (digital push). Full well at base ISO is about 51,834 electrons; unity gain is around ISO 330.

Sony a900 vs Sony a99 read noise table

ISO	Sony a900	Sony a99
50	–	1.141
64	–	1.301
80	–	1.495
100	1.057	1.310
125	1.404	1.495
160	1.526	1.729
200	1.444	2.042
250	1.505	2.428
320	2.028	2.868
400	2.445	3.458
500	2.969	4.228
640	3.837	5.205
800	4.563	6.453
1000	5.502	8.112
1250	7.210	10.126
1600	9.781	12.729
2000	11.551	16.000
2500	14.825	20.112
3200	19.027	25.457
4000	22.471	32.000
5000	28.840	40.504
6400	36.758	50.563
8000	–	63.558
10000	–	80.449
12800	–	101.125
16000	–	128.000
20000	–	162.017
25600	–	200.854

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