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Pentax K20D vs Pentax KP: read noise comparison

Dual gain: Pentax K20D none, Pentax KP ISO 400.

Pentax K20DDxO

The Pentax K20D was measured at 7 ISO settings from ISO 100 to ISO 6400. Values were derived by Bill Claff from DxOMark lab data.

At base ISO (100) read noise is 2.55 DN. From ISO 3200 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise.

Pentax KP

The Pentax KP was measured at 40 ISO settings from ISO 100 to ISO 819200. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 1.83 DN, or 4.1 electrons at the sensor. A second gain (dual gain) kicks in at ISO 400, cutting input-referred read noise by about 1.2 stop. From ISO 4000 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 204800 don't change analog gain (digital push). Full well at base ISO is about 36,953 electrons; unity gain is around ISO 230.

Pentax K20D vs Pentax KP read noise table

ISOPentax K20DPentax KP
1002.5491.828
125–2.235
160–2.585
2004.9933.227
250–4.000
320–4.627
4007.5162.567
500–3.182
640–1.790
80011.3141.892
1000–2.313
1250–2.639
160016.2233.249
2000–3.891
2500–4.627
320019.2936.021
4000–7.464
5000–8.815
640037.27110.703
8000–13.737
10000–16.223
12800–20.393
16000–28.840
20000–32.000
25600–43.713
32000–57.282
40000–66.257
51200–90.510
64000–129.787
80000–140.070
102400–179.769
128000–256.000
160000–280.139
204800–382.681
256000–512.000
320000–552.565
409600–765.363
512000–1,105.130
640000–1,160.073
819200–1,686.714

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Data: Photons to Photos · © William J. Claff