Nikon D3X vs Nikon D40: read noise comparison

Input-referred read noise at base ISO: Nikon D3X 5.9 e⁻ (ISO 100), Nikon D40 11.9 e⁻ (ISO 200).

Nikon D3X

The Nikon D3X was measured at 20 ISO settings from ISO 50 to ISO 6400. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 2.06 DN, or 5.9 electrons at the sensor. From ISO 200 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 1600 don't change analog gain (digital push). Full well at base ISO is about 46,773 electrons; unity gain is around ISO 280.

Nikon D40

The Nikon D40 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 1.96 DN, or 11.9 electrons at the sensor. From ISO 200 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 1600 don't change analog gain (digital push). Full well at base ISO is about 24,849 electrons; unity gain is around ISO 1210.

Nikon D3X vs Nikon D40 read noise table

ISO	Nikon D3X	Nikon D40
50	2.056	–
64	2.056	–
80	2.056	–
100	2.056	–
125	2.770	–
160	3.458	–
200	2.828	1.959
250	3.555	–
320	4.724	–
400	5.979	3.411
500	7.111	–
640	8.877	–
800	11.236	7.362
1000	13.929	–
1250	17.509	–
1600	21.706	14.420
2000	27.096	–
2500	34.060	–
3200	42.814	39.124
6400	86.823	–

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