Pentax 645D vs Pentax K-1: read noise comparison

Input-referred read noise at base ISO: Pentax 645D 14.5 e⁻ (ISO 100), Pentax K-1 3.1 e⁻ (ISO 100).

Pentax 645D

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 K-1

The Pentax K-1 was measured at 30 ISO settings from ISO 100 to ISO 204800. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 1.20 DN, or 3.1 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 51200 don't change analog gain (digital push). Full well at base ISO is about 41,653 electrons; unity gain is around ISO 250.

Pentax 645D vs Pentax K-1 read noise table

ISO	Pentax 645D	Pentax K-1
100	6.063	1.197
125	6.869	1.444
160	8.112	1.659
200	10.483	2.042
250	13.269	2.532
320	15.562	2.928
400	20.252	3.605
500	26.173	4.595
640	31.125	5.352
800	40.504	6.727
1000	52.346	8.634
1250	62.250	10.196
1600	80.449	13.086
2000	–	17.630
2500	–	19.973
3200	–	25.992
4000	–	34.060
5000	–	40.224
6400	–	51.984
8000	–	68.594
10000	–	79.341
12800	–	103.968
16000	–	138.141
20000	–	158.683
25600	–	206.500
32000	–	266.871
40000	–	315.173
51200	–	404.501
102400	–	809.002
204800	–	1,606.828

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