Hi there, Nico Carver here, I get a fair amount of questions about shopping for astronomy
cameras and which specs are important, and so I thought a tier list where I’d rank
the specs is a fun way to discuss this, which is a fairly dry and technical topic.
And I’ll rank how important the different specs are to ME, but keep in mind I am a deep
sky astrophotographer who mostly take photos of nebulae as the name of this channel suggests
so the considerations would be very different if we were talking planetary or lunar or even
high resolution astrophotography. different things sorta change calculus
Alright here we go, a CMOS vs a CCD sensor.
I’ll rank this E. I’m tempted to rank it F. To me the whole CMOS vs CCD thing often
plays out like the Sony vs. Canon war in regular cameras.
Where people take sides just based on what they own and don’t really
listen or the think they know what's best and for most use cases it really doesn’t matter to the actual
results whether your camera has a CMOS complementary metal oxide semiconductor sensor or a CCD
charge coupled device sensor.
Now, with that said, the reason I’m giving this an E and not an F is there is one use
case where it does matter and that is for binning pixels together, and what binning
is it’s where you instruct the camera to treat a 2x2 or 4x4 array of pixels as one
super pixel, and while we can ‘software bin’ pixels just by re-sampling the image,
hardware binning is something that is only possible with CCDs not CMOS.
So if binning is a deal breaker for
you and this is really an advanced thing not something someone new should worry about then
the CCD vs. CMOS spec matters,
Next one is sensor size, and I’m going to put this one A tier.
While you can get great results with a small sensor, you can also just always crop a larger
sensor.
And there are times when the larger sensor can just save so much time with really no
drawbacks other than cost.
And the costs do spiral, especially if you go mono, because then you are talking bigger
filters too.
But let me give you an example, I moved from a micro 4/3s asi1600 to an APS-C sized qhy268m
recently and a big mosaic I was working on went from 66 panels to 35 panels with no drawback
as the pixel size is the same between the two cameras.
So covering more area of the sky in less time is almost always a plus for me as someone
who loves big emission nebulae and mosaics.
Okay resolution, meaning total number of pixels.
This one I’m just not gonna rank because it’s just a function of the physical sensor
size and pixel size, both of which are already listed here, and are the actual specs we want
to talk about, so I’m just gonna delete this icon.
Analog to Digital Converter bit depth.
I’m going to rank this one C. And will say this one is often misleading to people as
just because the ADC can handle that range of brightness values doesn’t mean that it’s
necessary with the actual dynamic range of the sensor.
For instance, my ASI1600 has a 12 bit ADC, but that is not a real limitation because
I’m usually shooting with a high gain and very limited dynamic range anyways.
Next one is Read Noise.
I am convinced based on the consensus of many astrophotographers that are smarter than me
and that I trust completely that this is a very important spec.
You want read noise to be low obviously.
This gives the camera much more flexibility to take short exposures that aren’t as noisy.
If you have high read noise, you ideally need to take much longer exposures so that you
can effectively swamp the read noise.
And for me I like the shorter exposures I love taking 5 min to 10 min.
Narrowband exposures and 2 min.
Broadband and f/5.4 because you then I don’t have to feel so guilty about throwing out
data that is sub-par while if I was taking 30 minute exposures I’d feel much more possessive
about each sub.
So I’m all in on low read noise, I think it’s a superior spec.
Cooling performance.
I’m gonna take this one to just mean having a set-point cooler, and rank it also S. Being
able to consistently set the camera to a set temperature means you can create libraries
for your master darks at different gain and temperature settings and that has been a god
send in how much time I save only taking new darks once a year, maybe even once every two
years.
Okay an image buffer, I’ll rank this one C but I’ll admit I don’t really know how
important it is.
my asi1600 was an early model that didn’t have the buffer and I’ve never had a problem
with data transfer using sequence generator pro, but I’m sure it’s probably there
for a reason as most of the astro cameras seem to have it nowadays.
Full well capacity.
This one I will put at B. in combination with read noise it’s a reflection of the sensor’s
actual dynamic range unlike the ADC bit depth.
And if you do a lot of broadband work where having that larger dynamic range is important
then this may be an important spec to you.
USB speed, for deep sky I gotta put this one at F because it doesn’t matter.
Having fast transfer speeds only matters for planetary, lunar that kinda thing where you
trying to max out video framerates for lucky imaging.
Pixel Size.
I will put this one B tier.
The pixel size and the focal length of your telescope is what changes your image scale
or how finely you are sampling the night sky, which theoretically determines the smallest
details you can resolve.
And knowing about this spec IS important.
But I don’t think it’s as important as read noise or sensor size.
And I’ll have to do another video on image scale and pixel pitch as I think people usually
over-simplify it and don’t get enough into seeing conditions and dawe’s limit and other
practical limits to how much we can hope to resolve with smaller and smaller pixels.
So I don’t have time to go into all that now, but some other five minute friday I’ll
do it.
Quantum efficiency.
This is a measure of how well a camera actually converts photons to electrons that are then
counted and turned into the image data.
And this is a particularly important spec for deep sky since we are dealing with very
few photons, so every photon counts as Steve Richards says.
I will put this B tier.
It’s important, but be careful with graphs and do your homework, because what we are
really interested in is absolute QE and to be able to compare cameras in terms of their
absolute QE at the different wavelengths you are interested in, while often what we get
is a relative QE graph which is only measuring how well the camera does at different wavelengths
based on it’s best performance, which is usually in the green part of the spectrum.
Frames per second.
This one gets an F for deep sky, it’s very important for planetary, lunar, and solar
where shooting video and doing lucky imaging technique, but for deep sky it doesn’t matter as much
Okay and that’s it.
Hopefully this was a good mix of information and opinion.
If there is any part of this that you want me to go deeper on, let me know in the comments.
Till next time this was Nico Carver Nebula Photos dot com.
Clear Skies!