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Old 31-01-2010, 01:53 PM
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telecasterguru (Frank)
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CCD camera primer

Is there an easy to read CCD camera learners document that explains the pros and cons of different sized pixels, over/undersampling, well depth etc and what they actually mean in the real world?

What sort of camera is suitable for long focal length SCs as compared to short focal length newts or medium focal length refractors. Does it matter? If I put a focal reducer on my SC does that mean the optimal camera for my system will change? Once again does it matter?

I have tried to read as much as I can so that I can make an informed decision before buying a CCD camera but I don't understand a lot, make that most, of the jargon or how it actually translates into images through a telescopes.

I don't suppose there is a magic formula to all this but I would at least like to understand what I am reading.

Frank
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Old 31-01-2010, 02:09 PM
Mighty_oz (Marcus)
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The SBig site has a bit of info on the camera's etc eg the 8300 chip one has a chart re focal lengths vs pixel size/binning that's usefull.
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Old 31-01-2010, 03:34 PM
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Frank

I found the Apogee CCD University site very informative.

There is a discussion about pixel size here

James
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Old 31-01-2010, 08:09 PM
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this may help

http://www.clarkvision.com/articles/...ry/#read_noise
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Old 01-02-2010, 10:12 AM
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Frank, like you I went through a lot of this before buying my current camera.

Some pieces of advice I got.

ATS has a formula to work out your sampling rate for any given pixel size. The basic premise is that you need your sampling to be about 2x as good as you average seeing. So in my case I get around 1 arc second of average seeing on any given night. I need to sample at 0.5 arc seconds. The KAF8300 gives me around 0.68 with my RC. However I could use the STL6303 and get better results and still be sampling at a good rate.

In reality though I have read that 0.80 arc seconds is fine for most scopes. The old 2 seconds or arc per pixel seems to be pretty much out. I could be wrong but that seems to be the case.

Well depth - this is how much charge the pixels can take before saturating and more importantly how long you can image for. Any sensor that has a higher well depth is apparently considered as being superior. Sensors that have pixels the size of 7.4 and 9 are considered to have good well depth. The KAF8300 has a well depth of only 5.4um. Not great for star sizes at high mag but good for sampling. You might now be seeing the picture. It also means that you can only image for 10-15 minutes with an 8"RC with that size pixel. Personally, when I buy again I will be looking at a pixel size of 9um to get the better well depth. Star bloat becomes less a of a problem from what I have seen. Stuart's (Rat) images show great stars because he has less bloat caused from larger pixels in his ST10.

Pixel size - related to above but also determines the bloat of your stars or whether you get round or square stars. If your pixels are larger than 9um then you are likely undersampling and this creates square stars (not wanted). If you are using pixels smaller than 9um then you are really over sampling and this creates very round stars but they tend to bloat because more pixels are filled with charge and this gives the stars a larger look. Over sampling is good for image sharpening but no good for star size.

Like I said, the KAF8300 is probably best suited for refractors with its smaller pixels (I will be using mine for the very same thing when I buy the next CCD). Try looking at something around 9um for your RC. Ask Peter Ward or Martin Pugh. I am sure they will tell you the same thing.
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Old 01-02-2010, 11:42 AM
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telecasterguru (Frank)
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Paul,

Thanks for the advice and it does make sense.

My problem though is that I want the best of both worlds as I also want to image with my ED127 as well as the RC10".

Frank
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Old 01-02-2010, 02:02 PM
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Hi Frank, there's a good few tips here to work out your image scale. Knowing your FL and aperture you'll be able to work out the ideal pixel size on your CCD depending on what you wish to image. I think as a rough rule close to 1 - 1.5 second of arc per pixel is the sweet spot.
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Old 01-02-2010, 02:08 PM
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I'm kinda in a same boat researching on ccd's at the moment.

Sorry if this is a stupid question but can't seem to find a definite answer to this,
Would binning modes help prevent star bloating as mentioned above, if I binned to match a suitable image scale?
or is it just not the same as having the right physical pixel size?

I have a brand new RC8 which hasn't seen it's 1st light because I'm still waiting on a CCD.
I am on a waiting list for a KAF8300 camera but it seem it is not optimal for RC8 and RC10,
thus I started looking into KAI 04022 based camera with ATIK4000LE in my budget range....
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Old 01-02-2010, 05:45 PM
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Zipdrive you can use the KAF8300 but star bloat is gonna plague you with longer focal length. However, the main advantage to its use is that you can sharpen your images a long way as a result of the over sampling.

I use binning to gather my colour data and unbinned for my Lum data. I really think binning everything will be causing more harm than good.

Frank, if you got the 6303 then your refractor will give you wonderful images as well as your RC producing wonderful images.
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Old 01-02-2010, 06:52 PM
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First of all I have a st4000xcm with a kaf4022 chip, with 7.4 micron pixels. I image at 1800mm and I end up with an image scale of .85 seconds of arc per pixel. Its pretty much at a sweet spot at that level, especially with Adaptive Optics. I'm pretty much stoked with its performance.

Well depth from memory is around 55000e with the KAF4022 and 25000e for the 8300. I'd be very interested to see how the 8300 performs when bin 2 as regards star bloat at longer fl's.
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Old 01-02-2010, 08:04 PM
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Paul,

The 6303 looks the goods but as you said it is fairly (very) expensive compared to the 8300.

I am still reading and trying to come to terms with it all and am getting a little closer to undestanding what it all means.

One question though, is -3e better than -12e or vis versa? Not sure about what this actually means. Big chips seem to have -12e while small chips have -3 or -4.

If -e is the electrons gained by a chip, is the smaller number better and therefore mean less noise? Does a smaller chip gather less noise simply because of its size or is it relative to the pixel size?

Frank
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Old 02-02-2010, 09:00 AM
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Frank I am assuming you are referring to electrons caused from dark current. In that case I think the smaller number is the better of the the two. Not 100%, you will need to ask someone a bit more in the know.
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Old 02-02-2010, 03:32 PM
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why not the QHY 8 7.4 um pixel size

Ok so it's only 6 mp

but this is what it can do

http://qhyccd.com/ccdbbs/index.php?topic=1357.0
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Old 02-02-2010, 06:47 PM
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Dont forget the 6303 is NABG (non anti blooming gate) and the 8300 ABG, you pay for extra QE, both in money and convienience. Low well depth and NABG can both cause blooming, for different reasons.

Lower dark current is better, it can affect dynamic range.

Ideal image scale nowadays is not so simple to define, Martins http://www.martinpughastrophotograph...aLRGBFinal.jpg with a 16803 was at 3.5 arc/secs/pixel and it looks great. Horses for courses, image SIZE counts now.

Others say sub 0.6 arcsecs/pix is the go, it depends image size and on how the final full frame view looks.
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Old 02-02-2010, 08:03 PM
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If you are thinking about a STL6303 they are availiable as NABG and ABG.
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Old 02-02-2010, 09:03 PM
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Quote:
Originally Posted by bert View Post
If you are thinking about a STL6303 they are availiable as NABG and ABG.
Kodak now only offer the NABG version.
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Old 03-02-2010, 06:26 AM
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Quote:
Kodak now only offer the NABG version.
Straight from the horses mouth.

On the specs on the sbig site should be updated, and on the other hand if you ordered a 6303 with abg its kinda like ordering aferrari with a diesel motor anyway.

Brett
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