Monochrome CCD vs Color CCD

Dear All,

the debate is raging on the forums here in France between filterwheel partisans and one shot color adepts… Having a DSLR culture, when I progressed to CCD, I ordered a color sensor despite people telling me color CCD were no good and produced pale images as well as being alot less sensisitive. Well, I, on the other end, liked the idea of being able to shoot my favorite objects pretty much in the same way as I did with the old Canon 350D… 9 months after having bought my camera, all I have to say is I have no regrets about choosing color over monochrome. The other day, i even managed to shoot 3 galaxy in one night, and get some sleep as well!

So lets look at the filterwheel clan arguments: a color camera is alot less sensitive than a monchrome one. Ok, good job I own an Atik11000-CM whose sister is the Atik11000-M as both use the very same KAI-11002 Kodak sensor apart from the microlenses on the color chip being… colored! So the only thing that will change is the quantum efficiency due to the filtering effect of the bayer matrix. The curves below are pulled from Kodak datasheet: color-bw_0

The black line is the efficiency of the “mono” camera, while the colored lines are the efficiency of  the color channels on the color camera (I hope you’re not daltonian). Well, it does not appear “alot” less sensitive to me, but only a little less (around 15%).

Now what of the second argument: pictures taken with a color camera have no life in them since there is no luminescence channel. Well, that’s what I call “thinking inside the box” as they are so used to their LRGB technique, that they forget that upon convervion from bayered FITS format to color Fits format, Luminescence channel is synthatised from the 3 color channels.

In conclusion, personally, I am very happy with the results I get from my color CCD, and I encourage anybody who wants to image the sky in a practical manner without the hassle and the added cost of filter wheel to use color cameras. Also, please mark my word, I strongly believe the days of monochrome cameras to be over soon, as color sensors become more performant.

Serge

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4 Responses to “Monochrome CCD vs Color CCD”

  • Yannis Doukakis says:

    You are comparing apples to oranges. The correct way to interpret the sensitivity of Mono compared to OSC is to compare the area enclosed between one of the colors, (R,G,B) and the X axis, to the area enclosed by L and the X axis.

    It is easy to see that any OSC sensor is doomed to 1/3 the sensitivity of the Mono.

    In other words, if three photons, one R, one G and one B arrive at one pixel, the Mono sensor will register all three, the OSC sensor will register only one of them.

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    • admin says:

      Yannis,
      you are perfectly correct in that respect when you consider a single channel! Mathematically, to compare sensitivity of OSC to mono, you would have to compute the area enclosed by the curves for Red, Green and Blue (in other words perform an integration) and compare that to the result from the mono. There is a flaw in your reasoning since OSC sensor software are smart enough to compute synthetic luminance by adding
      adjacent pixels. So, a single pixel is the result of 2 green, 1 red and 1 blue. The drawback of this is that at pixel level, your image will be less contrasted.
      It would be well known if OSC was as much as a third of a mono sensitivity! At the moment, and this is proved by practice OSC’s sensitivity is 80% of mono. I should know, since we did the test on my C14 with a friend who owns a mono STL11000; which I doubt you have. For a deeper insight ino this please refer to “how does a color camera interpolae pixels?” article on this site. It explains alo.

      Serge

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  • Serge, I am wondering if you are still as enthusiastic about OSC and if you have had a chance to do more comparisons. I too am shooting with an Atik 11000C and felt I needed to go to a monochrome version. I find myself doing 9-15 hours for sufficient smoothness in my dark sky. I am shooting at a slow f/9. Feel free to write me directly. Thanks!

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  • admin says:

    Hi Warren.
    Nice website you’ve got! Also, I really envy your New-Mexican sky!!!
    Well, to answer your question, no, I haven’t had the chance to carry out more tests, as my friend with the monochrome 11000 lives far away. Now, my experience of the OSC camera is that, yes, it can be a struggle to shoot very faint objects, especially if, like for me, sky glow is not negligeable. So, On some nights, I am thinking about switching to monochrome and some nights, I don’t (it’s dependant on my target at the time). Now, the most important thing is that a monochrome camera will not bring a huge leap in sensitivity, only about 30% from what we did see. Now, the thing that makes a mono camera an OSC killer is when you use Halpha filters on it (which you can’t do on a colour camera). With a filter, you can shoot extremelly faint nebulas and get no sky glow whatsoever.
    That being said, having a reflex camera culture, I like the ease with which I can process a color image from the OSC without having to mess about with filters. The best of both worlds would be to have a mono CCD to do Luminance layer and the OSC for colours! you can do luminance one night, and acquire 4 hours of colour which should be enough.
    Also, one thing you have to keep in mind is that the KAI-11000 be it mono or color, are interline sensors, which are nowhere near as sensitive as fullframe sensors such as the KAF-8300. Just do not expect miracles even with the monochrome KAI-11000, that is, unless you’ve already bought it and you really feel there’s a huge difference?

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