Pentax 645Z vs Pentax ist DL2: read noise comparison

Input-referred read noise at base ISO: Pentax 645Z 3.5 e⁻ (ISO 100), Pentax ist DL2 17.4 e⁻ (ISO 200).

Pentax 645Z

The Pentax 645Z was measured at 34 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 1.19 DN, or 3.5 electrons at the sensor. From ISO 640 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 2500 don't change analog gain (digital push). Full well at base ISO is about 48,430 electrons; unity gain is around ISO 290.

Pentax ist DL2

The Pentax ist DL2 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 3.01 DN, or 17.4 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 22,944 electrons; unity gain is around ISO 1160.

Pentax 645Z vs Pentax ist DL2 read noise table

ISO	Pentax 645Z	Pentax ist DL2
100	1.189	–
125	1.474	–
160	1.670	–
200	2.099	3.010
250	2.585	–
320	3.010	–
400	3.758	3.531
500	4.691	–
640	5.426	–
800	6.821	7.013
1000	8.574	–
1250	9.987	–
1600	12.553	13.929
2000	16.336	–
2500	19.427	–
3200	19.973	28.051
4000	25.992	–
5000	31.125	–
6400	38.586	–
8000	50.213	–
10000	59.714	–
12800	59.714	–
16000	77.708	–
20000	92.411	–
25600	119.428	–
32000	154.343	–
40000	184.823	–
51200	213.783	–
64000	276.282	–
80000	328.557	–
102400	424.612	–
128000	548.748	–
160000	652.575	–
204800	837.532	–

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