Pentax K-S2 vs Pentax K100D: read noise comparison

Input-referred read noise at base ISO: Pentax K-S2 4.4 e⁻ (ISO 100), Pentax K100D 15.7 e⁻ (ISO 200).

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 K100D

The Pentax K100D was measured at 5 ISO settings from ISO 200 to ISO 3200. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (200) read noise is 2.62 DN, or 15.7 electrons at the sensor. From ISO 400 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 23,788 electrons; unity gain is around ISO 1200.

Pentax K-S2 vs Pentax K100D read noise table

ISO	Pentax K-S2	Pentax K100D
100	0.678	–
125	0.796	–
160	0.901	–
200	1.064	2.621
250	1.275	–
320	1.464	–
400	1.815	3.458
500	2.266	–
640	2.621	–
800	3.294	6.869
1000	4.228	–
1250	5.028	–
1600	6.498	13.454
2000	8.282	–
2500	9.781	–
3200	12.641	27.096
4000	16.223	–
5000	19.027	–
6400	22.785	–
8000	27.858	–
10000	26.538	–
12800	31.341	–
16000	40.786	–
20000	49.522	–
25600	63.558	–
32000	82.711	–
40000	97.006	–
51200	127.116	–

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