MONO vs OSC...no competitors?

Dietmar · #1 20-12-2007, 08:38 AM

hi guys,

8 weeks passed by without one single chance for decent astrophotography except 1st of november when I imaged the
comet:
http://www.stargazer-observatory.com/holmes2.html

these days we have clear skies with superb transparency,...but seeing is really at its worse! minus 10 on pickering's scale...
so I had some time to write up my thoughts covering the interesting topic
monochromatic vs OSC - quite frankly, I tend to feel, that these different types of CCD do not necessarily need to be competitors....but please find time to check this out:
MONO vs OSC:
http://www.stargazer-observatory.com/mono_vs_osc.html

I'd appreciate any comments and thoughts you might have.

I know we have discussed this a couple of times,...it's just my attempt, to beat the DSI-less time for me here,...

jase (Jason) · #2 20-12-2007, 09:18 AM

Good write up Dietmar. You've certainly captured the key points. I'd like to also open up a discussion for some other points (which I posted in another thread).

You'll still need to colour balance your images with a one shot colour camera. This is unavoidable. The workload is not as simple as many believe. You'll probably end up splitting out the individual R,G,B channels so you can manually work on them.
In some cases exposure times with the one shot colour need to be longer than that of a mono camera due to the reduced QE. Though many one shot colour CCD chips have improved QE that are close or equal to mono chips nowadays.
Regardless of the camera type, you'll still have battles dealing with light pollution and its associated gradients it will produce on your images. Mono does give you the edge if you want to use narrowband filters, though these can also be used with one shot colour cameras (but are less effective).
Something that I didn't think of which was mentioned in an SBIG post on one shot colour cameras; "There are problems with colour artefacts, because in anti-blooming versions, the individual colours start to hit the ABG, at different points. So if you image a 'blue' star, and approach the ABG, the blue colour gets attenuated relative to the other colours, resulting in great problems with colour balance across the image."
"There is also an artificial 'shift' induced by the positions of the different colour pixels, which results in displacement between the colours, as you start to approach being undersampled." Neither of these two issues occur using a mono camera with filters.

Quoted from your site:
"The real big advantage of a monochromatic CCD in my eyes is the better color data that can be achieved. In the option to use different color filters for all kinds of purposes, an OSC will always stay (a little) behind. OSC suffers (a bit) in color depth and color data of the stars. The only chance to work this problem is to go for real long total exposure time with long sub frames."

I couldn't agree more, but then again, mono imaging isn't for everyone. As you've also mentioned it takes considerable effort in pre/post imaging with filters and a mono chip. The work load is higher that's for sure. The OSC CCD is certainly a logical step up for those DSLR users wanting to improve the quality of their output.

avandonk · #3 20-12-2007, 09:46 AM

Good perspective on the relative merits of mono vs colour imaging.

My take on it is what people can afford. It is not an argument of what is best but but how much one wants to invest (waste according to SWMBO). Even my modified Canon 5DH cost many thousands of dollars. At least it can be used for terrestial photography and it really excels at low light.

I am sure as time goes by I will invest in a 'better' imaging sensor. Unless it can produce a markedly better result I will persevere with what I have.

Meanwhile I have worked out how to overcome the 12 bit limit on the Canon 5DH. I can also cool (-12 degC) the whole camera to minimise thermal noise and I have got a lot of experience and fun doing it.

I also think that if A Canon CMOS sensor was cooled to the same extent as any CCD it would leave it far behind. Without the Bayer filters the QE would be close as well. A 16bit or better A to D would also help.

There is never a 'correct' answer only the current 'best'.

The problem as always is that quality versus cost is a function that follows an inverse exponential.

Bert

Alchemy (Clive) · #4 21-12-2007, 09:56 AM

Liked the comet image Dietmar, im guessing its nice and cold in Austria.

As for the ccd , if i had the funds i would purchase the mono chip.
As i have only used a digital camera til now im not really qualified to comment BUT i do like the idea of narrowband, and occassionaly luminace only shots appeal, however i will readily admit that the images i have seen of yours are of an extremely high quality.

Dietmar · #5 21-12-2007, 10:33 AM

thanks Jase, Bert and Alchemy for your input.
Bert, as far as I am informed, CMOS chips are 12 bit chips,...CCDs 16 bit...at least it was in the years I was working with DSLR.
Jase, you are right in terms that mono has more flexibility for being used in different terms. as I indicated, OSC will lead to very good results in oversampling only, undersampling will sure lead to a loss of detail.
but - take a look around - Bud Guinn, Alan Chen, Warren Keller and so many more, their results should speak for themselves.
when OSC showed up on the makret, many believed they would always be inferior, and this is not true. that's all the article wants to point out.
so many considerations for decent DSI...more than just bayer or mono...
have a good time guys!

tornado33 · #6 21-12-2007, 04:36 PM

Where the mono comes into its own is with narrowband imaging. Each and every pixel can see the dim monochromatic light that narrowband filters let through. I wish Canon made a mono DSLR without the bayer filter array, ie a mono CMOS sensor. The onboard processor could be simpler too as only one channel to process.
Scott