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Old 04-03-2013, 10:03 PM
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Shiraz (Ray)
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Location: ardrossan south australia
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Quote:
Originally Posted by Peter Ward View Post
I'd honestly say my pedaling KAF based devices is a sideline...and I do try to keep any commercial biases out of any postings...that said..

I'm very much a user of Astro-imaging gear with KAF8300, KAF16803 and ICX694 senors (plus a number of Canon DSLR's) all being in my personal arsenal.

My KAF8300 does indeed saturate very quickly... but I'd not call 25% better performance a "little" improvement over the ICX694.

A boost in QE, for example, by 25%, is obvious when you look at the raw data.

I also think Sony's noise figures are a little rubbery...clever correlation filters that also scrub photon liberated electrons can easily make noise look good at the expense of subtle signal.

Also can you, or someone, point me to a SONY ICX694 data sheet with absolute QE?...I can only find 3rd party specs...which I frankly don't trust.

The only method I've read about...apart from deep cooling...that keeps thermal electrons in the background is "Skipper" CCD technology...sadly not commercially available as far as I am aware.

I suppose what I am still saying, when it comes to pixels, is: bigger = better.

The downside is, bigger (matching optical systems) often cost a whole lot more....
I guess we will just have to disagree Peter.

On the quantum efficiency issue, Clive's post points to an independent evaluation that compared the 694 directly with a 3200 - the measured QE was consistent with those published by such third parties as Apogee, Atik, Pt Grey etc. It really is very high.

I also think Sony's noise figures are a little rubbery...clever correlation filters that also scrub photon liberated electrons can easily make noise look good at the expense of subtle signal.
????? If Sony had found a way to get rid of noise and not signal, they would own the telecommunications world - they don't. What they are actually doing is more likely to be something like MPP, which is discussed some way through this: http://learn.hamamatsu.com/articles/ccdsnr.html

Note also the equation for dark current

D = 2.5 1015 A Id T1.5 e-Eg / (2kT) where A is the pixel area - which means that dark current is directly proportional to pixel area - big pixels are not necessarily better.



Quote:
Originally Posted by clive milne View Post
Ray,
you might find this interesting:

http://www.astrosurf.com/buil/isis/noise/result.htm

Christian Buil presents a noise and electronic gain evaluation of a sample of astronomical CCD cameras including; KAF8300, KAF1603, KAF16803, KAF3200, KAF402, KAF11000, KAI2020, ICX694, ICX285.
Thanks for that Clive - a very useful resource and points out how good your 3200 is.

Quote:
Originally Posted by gregbradley View Post
Hi Rally,

An interesting thread. I agree sampling is definitely an important factor and matching pixel size to focal ratio is a well known datum. 1 arc second per pixel is one approximation that AP recommends and others use .66 arc seconds per pixel as being more specific to using the Nyquist sampling theory in application (3 times sample is better than the minimum 2X).

As far as gain goes in 8300 chip I don't know anything about that so I take your work for it.

As far as small pixels will have low well depth and thus likely to show white stars - I have seen examples of better looking stars in shorter exposures in fast scopes. Longer scopes probably less of an issue but then too long a focal length and the small pixels are no longer giving you proper sampling and as you point out you lose sensitivity. I have seen that with my own eyes and this is true.

As far as small pixels not having large dynamic range I think that has some assumptions. It is assuming the same read noise and as the post linking Christian Buils work on measuring some of these common chips you can see the Sony chip is in totally another league with lower read noise whilst higher QE. As dynamic range is a function of read noise (too much read noise and you lose differentiation between some levels of shadow or brightness).

As I thought Sony is totally out in front with clear air from other sensor manufacturers and are leaving them all in the dust. Canon is several generations behind Sony. Sony is also just going from strength to strength. They just last week signed a cross sharing of imaging patents with Aptina who has a huge number of imaging patents. Aptina often make excellent sensors for Nikon cameras for one.

So that means Sony will have access to Aotina's technology to actually increase well depth on any sensor of any pixel size. There is a video of Aptina President describing the technology.

A few years of development at this rate and we'll all be using some sort of hitech CMOS sensor unless True Sense releases some new advanced chips. Probably a while yet but I already see the signs.

My prediction is this 694 chip will be very very hard to beat and will see a lot of people switching their 8300 cameras for one or at least new buyers going to the Sony Darkside.


Greg.
thanks for the summary Greg. Interesting that Aptina is tying up with Sony - they have some incredible small pixel technology - did you read the future directions white paper on their website? If only some of these guys would make some of their excellent DSLR chips without the Bayer filters - one would think it would not be that hard to do. Problem is probably that nobody high up in Sony is even aware that there is a tiny amateur astronomy market or that some of their chips find their way into it.

regards Ray

Last edited by Shiraz; 04-03-2013 at 10:51 PM.
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