TREN
Pentax 645D read noise vs ISO
The Pentax 645D was measured at 13 ISO settings from ISO 100 to ISO 1600. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.
At base ISO (100) read noise is 6.06 DN, or 14.5 electrons at the sensor. From ISO 125 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 39,235 electrons; unity gain is around ISO 240.
Pentax 645D read noise table
| ISO | Read noise (DN) | log₂ |
|---|---|---|
| 100 | 6.063 | 2.60 |
| 125 | 6.869 | 2.78 |
| 160 | 8.112 | 3.02 |
| 200 | 10.483 | 3.39 |
| 250 | 13.269 | 3.73 |
| 320 | 15.562 | 3.96 |
| 400 | 20.252 | 4.34 |
| 500 | 26.173 | 4.71 |
| 640 | 31.125 | 4.96 |
| 800 | 40.504 | 5.34 |
| 1000 | 52.346 | 5.71 |
| 1250 | 62.250 | 5.96 |
| 1600 | 80.449 | 6.33 |