Sigma fp vs Sigma fp (CL): read noise comparison
Dual gain: Sigma fp ISO 640, Sigma fp (CL) none.
Sigma fp
The Sigma fp was measured at 31 ISO settings from ISO 100 to ISO 102400. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.
At base ISO (100) read noise is 1.39 DN, or 6.8 electrons at the sensor. A second gain (dual gain) kicks in at ISO 640, cutting input-referred read noise by about 1.3 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 74,884 electrons; unity gain is around ISO 490.
Sigma fp (CL)
The Sigma fp (CL) was measured at 12 ISO settings from ISO 6 to ISO 80. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.
Sigma fp vs Sigma fp (CL) read noise table
| ISO | Sigma fp | Sigma fp (CL) |
|---|---|---|
| 6 | – | 0.582 |
| 8 | – | 0.707 |
| 10 | – | 0.570 |
| 12 | – | 0.801 |
| 16 | – | 0.835 |
| 20 | – | 0.973 |
| 25 | – | 1.173 |
| 32 | – | 1.231 |
| 40 | – | 1.173 |
| 50 | – | 1.625 |
| 64 | – | 1.625 |
| 80 | – | 1.625 |
| 100 | 1.395 | – |
| 125 | 1.376 | – |
| 160 | 1.385 | – |
| 200 | 1.404 | – |
| 250 | 1.659 | – |
| 320 | 2.028 | – |
| 400 | 2.908 | – |
| 500 | 4.257 | – |
| 640 | 2.114 | – |
| 800 | 2.085 | – |
| 1000 | 2.085 | – |
| 1250 | 2.042 | – |
| 1600 | 2.497 | – |
| 2000 | 3.074 | – |
| 2500 | 3.811 | – |
| 3200 | 4.659 | – |
| 4000 | 5.696 | – |
| 5000 | 7.062 | – |
| 6400 | 8.754 | – |
| 8000 | 10.853 | – |
| 10000 | 13.454 | – |
| 12800 | 16.795 | – |
| 16000 | 20.535 | – |
| 20000 | 25.992 | – |
| 25600 | 32.223 | – |
| 32000 | 38.854 | – |
| 40000 | 50.563 | – |
| 51200 | 63.119 | – |
| 64000 | 79.893 | – |
| 80000 | 97.681 | – |
| 102400 | 127.116 | – |
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