Pentax K-3 III Monochrome vs Pentax K-5 read noise comparison

Pentax K-3 III Monochrome

The Pentax K-3 III Monochrome was measured at 40 ISO settings from ISO 200 to ISO 1638400. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (200) read noise is 1.96 DN, or 3.5 electrons at the sensor. A second gain (dual gain) kicks in at ISO 800, cutting input-referred read noise by about 1.1 stop. From ISO 800 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 29,017 electrons; unity gain is around ISO 360.

Pentax K-5DxO

The Pentax K-5 was measured at 11 ISO settings from ISO 80 to ISO 51200. Values were derived by Bill Claff from DxOMark lab data.

At base ISO (80) read noise is 1.13 DN. From ISO 25600 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise.

Pentax K-3 III Monochrome vs Pentax K-5 read noise table

ISO	Pentax K-3 III Monochrome	Pentax K-5
80	–	1.133
100	–	1.485
200	1.959	2.676
250	2.378	–
320	2.888	–
400	3.630	4.563
500	4.317	–
640	5.426	–
800	3.117	8.398
1000	3.891	–
1250	4.823	–
1600	5.938	13.929
2000	7.464	–
2500	9.126	–
3200	11.392	46.851
4000	14.825	–
5000	17.388	–
6400	21.857	93.701
8000	28.051	–
10000	32.447	–
12800	42.224	196.720
16000	50.914	–
20000	41.070	–
25600	50.213	349.706
32000	65.799	–
40000	81.572	–
51200	102.537	604.668
64000	129.787	–
80000	158.683	–
102400	200.854	–
128000	252.476	–
160000	315.173	–
204800	404.501	–
256000	501.463	–
320000	625.992	–
409600	786.880	–
512000	989.119	–
640000	1,234.747	–
819200	1,530.726	–
1024000	1,924.143	–
1280000	2,336.284	–
1638400	2,817.110	–

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Pentax K-3 III Monochrome vs Pentax K-5: read noise comparison