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Old 21-02-2013, 09:54 AM
garywiz
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CCD/CMOS with Digital Output vs. Video (SVID, Comp)

I have not yet embarked on Astrophotography as I have just started getting into astronomy with my first real kit. But, Astrophotography will not be far off, as it is a great interest of mine, so I have been "planning my attack" as it were.

I am primarily interested in cameras which can do video, as well as frame-integrated image capture (for various reasons).

However I am an electronics engineer and video expert, and I have been looking at two different types of cameras:

- CCD/CMOS cams like the Stellacam and Mallincam, designed specifically for astrophotography
- CCD/CMOS cams like those from Basler, designed for industrial low-light applications.

Though marketing literature for the Stellacam boasts "Best Astrophotography camera ever created!!", I actually find this quite hard to believe. Why? Because those cameras convert their CCD/CMOS output to composite video (or S-video, which has essentially the same D2A conversion problems).

Essentially video in the form of component, composite or S-Video is *always* inferior to direct bit-by-bit transfers from the sensor itself. I do not own one of these cameras, but assume that they are PAL/NTSC compliant, meaning that they have all the requisite quality loss problems that any D2A converter will have when converting raw sensor data to what is now an archaic video representation format which is not only analogue, but is prone to noise, cable problems and so forth. Worse, these video-based cameras require that you have a A2D capture converter on a PC, meaning that the camera converts D2A (one potential loss area), the cable transmits analog data (another potential loss area), and the capture card (the most significant potential loss area because of the spotty quality of these devices) converts it yet again back into the digital signal that is captured by video or imaging software.

By contrast, a camera like those from Basler (such as the ACA640-100GM), allow direct capture of exact sensor data pixel by pixel, meaning that there is no possible loss, distortion, or conversion between the camera sensor and image capture.

Now, the decision is still not easy. Each of these cameras has its problems. For example, the BA 100GM above has known artifacts which may interfere with deep-sky photography. But, solving that is a matter of choosing the right industrial camera, the correct image sensor, and the right interface (GigaE or USB3) among the many many industrial manufacturers, which allows for a wide range and set of choices instead of the limited choices among "astrophotography webcam vendors".

I am posting to see if my above analysis makes sense, and whether there may be actual advantages I can't imagine that would justify the D2A-A2D losses incurred with video formats.

In fact, I can't even imagine why camera vendors like StellaCam and Mallincam would NOT use digital transfer, as their original sensors are digital. Am I missing something? It wouldn't be the first time!
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Old 21-02-2013, 10:52 AM
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ZeroID (Brent)
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I'm not an expert on this by any stretch of the imagination but it makes good sense to me. One of the advantages of video astro photography is that artefacts can be managed when the image stream is stacked so your problem in that regard may not be as bad as first thought.
Many retail webcams have been modified for astro purposes as you know and everytime a new, higher res or more sensitive model is released the first we hear of it is that someone is attempting astro mods to see how it goes.
I've looked at various industrial type webcams with an eye to conversion with their stated low light sensitivity being the crucial factor. can't see any reason why they shouldn't work given the right setup.

Looks like you've got yourself a project. Come up with a good build and they'll be knocking on your door.

I've gone down the 'DSLR and DSO' path astrophotgraphically but I have several modded webcams I keep meaning to find time to try some lunar or planetary imaging with. My DSLR has hires vid so it may even be pressed into action. Keep us posted.
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Old 21-02-2013, 11:06 AM
garywiz
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Thanks ZeriID, if I make any progress it probably won't be for a few months, but I will post things here, I just love this forum! (And astronomy!)

Right now I am just in the research phase, I may even build something from board level components.

One reason I want to go with video or frame-integration devices is that I have a Celestron 6SE with an AltAz mount. Obviously, longer exposures aren't going to work out, but the other day tracking 2012DA14, I realised that video could actually do justice to some subjects that still photography cannot.

On the other hand, I am sure I will eventually buy an EQ mount, but my theory is that fast exposure times and a good sensitive hi-res frame integration camera will just be even more useful on an EQ mount where there is greater lattitude for exposure. So, trying to get the photography setup on an AltAz mount for video seems a worthy cause and a good challenge.

It seems to me that even with an EQ mount, subtle vibrations could easily cause blur on long exposures unless you are meticulously careful (which I realise many people who do astrophotography actually are).
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Old 21-02-2013, 02:18 PM
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PRejto (Peter)
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Perhaps I am missing something obvious.....but, what exactly do you intend to image with this camera? Video would normally be reserved for solar system targets.
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Old 21-02-2013, 02:56 PM
garywiz
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Quote:
Originally Posted by PRejto View Post
Perhaps I am missing something obvious.....but, what exactly do you intend to image with this camera? Video would normally be reserved for solar system targets.
Well, I guess the first thing I'm wondering if it's worth questioning that assumption. For example, here is a page that describes (and has examples) of doing deep sky photography with a StellaCam II: http://www.lafterhall.com/stellacam2.html

There are many others. When I see things like this, I start thinking:
  • If you can do something "marginally acceptable" with an ST2, then clearly it must be possible with better technology.
  • There is far better video technology than the ST2 and any camera that outputs GigaE is going to deliver more precise versions of what's captured.
  • What is available today is better than what is available yesterday, so video technology may be "on the cusp" of being able to do more than it has in the past, where people restricted their use to planetary photography.

Obviously, if the goal is to create the very best Deep Sky images, long exposures using an excellent EQ mount and the best DSLR you can possibly afford will do the best job.

But is that really necessary? And, can we do better with CCD/CMOS than is currently assumed possible? It may open up the possibilities for higher speed captures and shorter exposures using frame-integrating cameras, something which DSLR cameras do not do (at least I am not aware of a frame-integrating DSLR).

That's the question I'm exploring.
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Old 21-02-2013, 03:45 PM
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lacad01 (Adam)
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Hi Gary, interesting reading this thread and likewise hope you can make some good inroads with your research. Devices like the Stellacam, G-Star, Mallincam, etc are capable of live view of deep sky objects not just planets or the moon. I know some guys have used Samsung low-light cctv cameras for deep sky live observing as well.
There's a pretty good video forum on CloudyNights that you should probably have a squiz through. I recently purchased one of these cheap low-light cameras from China and waiting to get some time to test it out properly but from the little time that I've had mucking around with it, it looks very promising. I just need to make a remote OSD box as the on-board buttons are tiny
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