Hurried reader? Skip directly to the test results below!
As many of you, I'd like to get the most from my cameras in
low light circumstances, such as under a dark sky. In the past I've
tested many of my cameras, and also of some of my friends. Here are the
To get reliable measurements, I've used the standard method for
measuring gain, i.e. the linear interpolation of points in a signal
versus variance graph. The protocol is well described in this page of Christian Buil
, a reference for this kind of tests.
I've captured a series of image pairs of a flat field, with exposure
times approximately between 6 s and 1/8000 s, using a standard lenses (i.e. 50 mm or 18-55 mm). I've used full
resolution raw format. I've analyzed only the green channel. I've
selected a 100x100 pixel crop near the part of image with minimum gradient
due to uneven illumination or vignetting.
I've measured gain and read noise at each ISO full stop from the minimum
to maximum setting of the camera (i.e. 100 to 3200
ISO), and -whenever possible- with the addition of 1000 ISO and 1250
ISO as a representative of 1/3 stops. I've tested also extended
sensitivities, when available.
To get the measurements from the raw files, I've used a custom made Matlab script.
The main results I've obtained are:
Results and list of the tested cameras
- Gain (inverse gain). Unit
of measurement: electron/ADU. This value shows the way an electron in a
pixel is converted to a number (ADU, Analog to Digital Unit). Please
note that gain is in truth the inverse of the gain (inverse gain):
common use has consolidated this error. So if you'd like to increase the
sensitivity you'll have to lower the (inverse) gain.
- ISO at unity gain. Unit of
measurement: ISO. This is the ISO sensitivity with an unity gain. Using
sensitivities below unity (or below 0.5, the limit is not sharp) should
not gain better results, but this is not true because the read noise
can decrease if the amplifier has a lower noise respect to the
acquisition electronics. Higher values, while comparing cameras with the
same number of bits, are synonymous of better results even if not always.
- Read noise. Unit of
This quantity is fundamental for low light subjects. Increasing ISO
sensitivity will usually decrease the read noise, and so this improves
the results on faint objects. But if increasing the ISO sensitivity over
a certain limit will not lower the read noise, then using this high
sensitivities is absolutely not useful, and also detrimental because the
dynamic range will be reduced.
- Dynamic range. Unit of
measurement: decibel.This is the ability to gather in the same image
faint and bright objects, without respectively loosing them in noise or
saturating. In these test the dynamic range is measured only
approximately because this is not of fundamental importance in
astrophotography. Usually the best dynamic range is obtained at the
lower ISO setting, but similar values can be obtained also for higher
- True sensitivities. A true
sensitivity is obtained by changing the analogical gain in the sensor
electronics. Another possibility is to "simulate" this sensitivity using
a simple software that multiplies the measured pixel values. In
example, a camera can obtain a 3200 ISO image by setting on the sensor
an analogical gain half of the one at 1600 ISO, or by setting the gain
at 1600 ISO
and then doubling the measured values. Clearly the software
manipulation will not get more information, and so this is of no use
(except if you shot in JPG format, not the case for most astronomical
imaging). Not only the software manipulation has no advantages, but it
has disadvantages, as a cut in half of the dynamic range (equivalent to
Here are all the tested cameras (ordered by introducing year). Click for detailed results. Here are only a few main results
Comparisons and notes
|Lowest read noise [e-]
|Highest advised ISO
|Best approx dynamic range [dB]
|ISO at unity gain
|Impressive sensitivity and low noise; but raw data is not raw and maybe some denoise is applied for the highest sensitivities|
|An improved successor of NEX-6 mirrorless, better for night imaging|
|First tested mirrorless; not good for night imaging|
|Canon EOS 5Dmk3|
|Most sensitive camera (up to test date, together with 6D)|
|Canon EOS 6D
|Most sensitive camera (up to test date, together with 5Dmk3)
|Canon EOS 60D RAW
|Tested, as usual with all cameras, with full raw format
|Canon EOS 60D sRAW
|Same test but with sRAW format
*** not true because of this format
|Canon EOS 60D mRAW
|Same test but with mRAW format
*** not true because of this format
|Auto noise reduction above 1600 ISO|
3200 and 6400 ISO are not true
*considering only true sensitivies
|Canon EOS 5Dmk2
|6400 ISO is not true
|Canon EOS 450D (modified with a Baader filter)
|Non linear quantization!!! At mid brightness only 10 bit are true.|
Denoise on raw data at all sensitivities above ~15% of dynamic range.
Auto noise reduction above 1600 ISO
*excluding noise reduced ISOs
|Canon EOS 20Da
|Canon EOS 5D (modified with a Baader filter)
|Canon EOS 350D (CHDK firmware)
|No real advantages of using CHDK
|SBIG STL 11000 (an astronomical CCD)
|Best true dynamyc range of any DSLR tested up to 2013.
|...more coming... do you want your camera tested? Contact me!
Comparing cameras of different epochs and sensor size shows the main
trend in technology
. While improvements are present, they are not so
large as one can expect: I assume the reason is mainly the mega-pixel
fever that seems not to stop. I'm confident that a newer camera with the
same mega-pixel count of an older one would have improved much more, with much better low light behavior.
In example, the dynamic range
has improved of about 2 dB from the 350D
of 2005 to the 60D of 2010. And the APS-C sized 60D was able to reach
nearly the same dynamic range of the full-frame 5D, a camera of 2005.
60D has improved very much the read noise
respect to 350D, but the merit
seems not to be due to the 14 bit analogue to digital converter (ADC)
(350D has 12 bit) because in example the 5D, with a 12 bit ADC, has
nearly the same dynamic range of 60D.
But due to the smaller pixel size, 60D is not so much more sensitive respect to 350D
, as also the detailed test of 60Da
The knee of the read noise curve
is in nearly all the tested cameras at
about 1600 ISO
(except 6D and 5Dmk3), so any sensitivity increase above this value has nearly
no advantages on the night time shots. So the large ISO values in 60D,
such as 6400 and 12800 ISO are only lark-mirrors...
On the contrary, the test of 450D shows that maybe a higher sensitivity
(maximum native is 1600 ISO) can improve the read noise,
as the read noise graph let imagine (the trend seems to decrease).
An improvement in newer cameras is the increased number of true
. In 60D all the sensitivities are true, and also
extended 12800 ISO seems to be true (even if this is of no use). Also in
350D and 450D all the standard sensitivities (100-200-400-800-1600 ISO)
the eventual other sensitivities possible thanks to CHDK are not true.
the 3200 ISO of 5D and 20Da are not true (however they are correctly named "extended" sensitivity by Canon).
A latest note about 6D and 5Dmk3, renowned among photographers because of their low
light sensitivity. The test evidence indeed a very good behavior, with a
knee in the read noise at 6400 and 12800 ISO respectively, that is much better respect e.g.
the 1600 ISO of nearly all other cameras (including 5Dmk2).
The drawback of Canon cameras seems to be the dynamic range. Even at the
lowest sensitivities the dynamic range is not very good. The best one
is 6D with 68.7 dB (corresponding to 11.4 EV, or 11.4 bit). This let
understand the usefulness of 14 bit converters (instead of 12 bit on
Here are my comments about non-Canon cameras I've tested.
The first is Pentax K-x
looking at the results, I would never buy such a camera because of the
many anomalies in the test results, such as 3200 and 6400 ISO
sensitivities that are declared true, but they are not, and because of
the read noise that does not decrease very much going from 200 ISO to
1600 ISO, giving nearly no advantage in terms of lowering noise when increasing ISO.
Another one is Nikon D90
. I was really impressed (negatively)
of this camera behavior. Even much much worser than the Pentax K-x. Many undesirable are present: the raw data is not raw
and by many aspects. Tree main problems are the cause of all problems:
1. non linear quantization: raw data are stored by loosing quantization
resolution in brighter pixels, leading e.g. to 10 bits instead of the
declared 12 bit at mid brightness. This is also associated with some
kind of noise reduction on bright pixels.
2. black level clipping: no offset is added before sensor data
acquisition, as is known from the ABC of data acquisition. Nikon ignores
deliberately this obvious rule imho for a deprecable reason: to fool
the image benchmarks looking at the read noise in bias frames. This way
nearly half of the noise is obtained. I've developed a method so that my
read noise measurements are not fooled by this behavior.
3. noise reduction (NR): above a certain ISO, a noise reduction
algorithm is applied to raw data! Even if it is turned off by the user.
This started in the first Canon-CMOS vs Nikon-CCD era, when Nikon
sensors have large dark signal (i.e. hot pixels); to hide the problem
Nikon added a firmware algorithm to cancel the hot pixels. Unfortunately
this removed also stars!!! Now that Nikon converted to CMOS, there is
no reason to keep NR!
As a conclusion: NIKON RAW IS NOT RAW AT ALL!!! This camera (and I
suspect all Nikons up to 2014) cannot be used for serious astroimaging.
Nikon, please, give us true raw data.
Here are my comments about astronomical CCD cameras I've tested.
The only one I've tested is SBIG STL 11000. Since sensitivity is fixed,
the only useful information is the dynamic range, quite large, and the
linearity, good up to 40000 ADU.