Pentax K-S1 vs Pentax K-S2: read noise comparison

Input-referred read noise at base ISO: Pentax K-S1 4.8 e⁻ (ISO 100), Pentax K-S2 4.4 e⁻ (ISO 100).

Pentax K-S1

The Pentax K-S1 was measured at 28 ISO settings from ISO 100 to ISO 51200. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 0.70 DN, or 4.8 electrons at the sensor. From ISO 400 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 4000 don't change analog gain (digital push). Full well at base ISO is about 27,917 electrons; unity gain is around ISO 680.

Pentax K-S2

The Pentax K-S2 was measured at 28 ISO settings from ISO 100 to ISO 51200. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 0.68 DN, or 4.4 electrons at the sensor. From ISO 10000 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 26,417 electrons; unity gain is around ISO 650.

Pentax K-S1 vs Pentax K-S2 read noise table

ISO	Pentax K-S1	Pentax K-S2
100	0.697	0.678
125	0.812	0.796
160	0.908	0.901
200	1.094	1.064
250	1.329	1.275
320	1.537	1.464
400	1.879	1.815
500	2.362	2.266
640	2.770	2.621
800	3.482	3.294
1000	4.408	4.228
1250	5.169	5.028
1600	6.681	6.498
2000	8.634	8.282
2500	10.196	9.781
3200	12.906	12.641
4000	16.450	16.223
5000	18.126	19.027
6400	19.698	22.785
8000	24.590	27.858
10000	26.173	26.538
12800	33.359	31.341
16000	42.814	40.786
20000	50.914	49.522
25600	65.345	63.558
32000	81.008	82.711
40000	93.054	97.006
51200	110.661	127.116

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