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Digital Cameras and Long Exposure Times:
Noise and Dark Current Comparisons

by Roger N. Clark

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They may not be used except by written permission from Roger N. Clark.
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How well do digital cameras perform during long exposures? On this web page, I'll show the details on digital camera dark current and compare some different sensors.

Canon 1D Mark IV Thermal Noise, Full Image, sub-sampled
Canon 1D Mark IV
ISO 1600
Exposure= 595 seconds
T= 0 C
Image Range:
-20.00 to 20.00 electrons about the mean

Full image statistics:
min= 0 electrons
max= 3652 electrons
mean= 533 electrons
standard deviation= 15.83 electrons

Canon 7d Thermal Noise, Full Image, sub-sampled
Canon 7d
ISO 1600
Exposure= 601 seconds
T= -4 C
Image Range:
-20.00 to 20.00 electrons about the mean

Full image statistics:
min= 203 electrons
max= 2457 electrons
mean= 308 electrons
standard deviation= 6.84 electrons

Canon 6D Thermal Noise, Full Image, sub-sampled
Canon 6D
ISO 1600
Exposure= 675 seconds
T= 1 C
Image Range:
-20.00 to 20.00 electrons about the mean

Full image statistics:
min= 703 electrons
max= 5213 electrons
mean= 759 electrons
standard deviation= 11.63 electrons

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Canon 1DX Thermal Noise, Full Image, sub-sampled
Canon 1DX
ISO 1600
Exposure= 600 seconds
T= 3 C
Image Range:
-20.00 to 20.00 electrons about the mean

Full image statistics:
min= 803 electrons
max= 5958 electrons
mean= 861 electrons
standard deviation= 17.38 electrons

Canon 1D Mark II Thermal Noise, Full Image, sub-sampled
Canon 1D Mark II
ISO 1600
Exposure= 623 seconds
T= 20 C
Image Range:
-20.00 to 20.00 electrons about the mean

Full image statistics:
min= 6 electrons
max= 3006 electrons
mean= 106 electrons
standard deviation= 50.76 electrons

Relative Stretch Images

Images stretched to show variation, not necessarily stretched to the same amount.


Canon 1D Mark IV, ISO 1600 505 secodn exposure, T= 13 C.


Nikon D7000, 600 second exposure, ISO 800, room temperature. Note: many pixels are truncated to zero.


Nikon D5100 601 second exposure, ISO 800, 82 degrees F ambient temperature. Some pixels are truncated to zero.


Canon 1D Mark II, 623 second exposure, ISO 1600, room temperature.


Figure 1a. A Canon 1D Mark II 5-minute dark exposure at ISO 800. Processing: standard curve raw conversion with default settings.


Figure 1b. A Canon 1D Mark II 5-minute dark exposure at ISO 800. Processing: standard curve raw conversion with default settings from Figure 1a, then scaled 0 to 10 DN in Photoshop using levels (this multiplies the image data by 25.5).


Figure 2a. A Nikon D50 5-minute dark exposure at ISO 800. Processing: standard curve raw conversion with default settings.


Figure 2b. A Nikon D50 5-minute dark exposure at ISO 800. Processing: standard curve raw conversion with default settings from Figure 2a, then scaled 0 to 10 DN in Photoshop using levels (this multiplies the image data by 25.5).


Figure 3. A Canon 1D Mark II 5-minute dark exposure at ISO 800 is compared to a Nikon D50 dark under the same conditions. Processing: standard curve raw conversion with default settings then scaled 0 to 10 DN in Photoshop using levels (this multiplies the image data by 25.5).

References

Night and Low Light Photography with Digital Cameras

1) CCD Gain. http://spiff.rit.edu/classes/phys559/lectures/gain/gain.html

2) Charge coupled CMOS and hybrid detector arrays
http://huhepl.harvard.edu/~LSST/general/Janesick_paper_2003.pdf

3) Canon EOS 20D vs Canon EOS 10D and Canon 10D / Canon 20D / Nikon D70 / Audine comparison
http://www.astrosurf.org/buil/20d/20dvs10d.htm

4) http://www.photomet.com/library_enc_fwcapacity.shtml

5) Astrophotography Signal-to-Noise with a Canon 10D Camera http://clarkvision.com/astro/canon-10d-signal-to-noise

Notes:

DN is "Data Number." That is the number in the file for each pixel. I'm quoting the luminance level (although red, green and blue are almost the same in the cases I cited).

16-bit signed integer: -32768 to +32767

16-bit unsigned integer: 0 to 65535

Photoshop uses signed integers, but the 16-bit tiff is unsigned integer (correctly read by ImagesPlus).

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First published September 1, 2006.
Last updated January 18, 2014