[AZ-Observing] Re: Monochrome Meade DSI

Sony does not generally give well depth in their CCD data sheets, you 
have to measure the saturation point and gain of the system and figure 
it out for yourself.  Typically the larger pixel Sony CCD's (such as the 
ICX248) have about 12ke- single pixel full well, maybe a bit more but 
linearity begins to break down badly as you approach the antiblooming 
point.  The serial register usually has a little less than twice this 
capacity, this allows about twice the dynamic range if binning in the 
parallel direction (and the gain is scaled so you can take advantage of 
it).  The output node is bigger still, allowing a similar increase when 
binning in the serial direction.  This is what allows you to get a real 
14 bit image if everything is set up properly with binning.

Yes, a big improvement over a webcam at eight bits, but still a fairly 
egregious lie in the data sheet.  Of course Starlight Express and others 
who use the Sony chips and 16bit converters are also guilty of this.

The other issues I have with the chips Meade is using is the 
rectangular, not square, pixels.  And, of course, the lack of cooling.  
The Sony CCD can achieve very good performance with only minor (~10-20C) 
cooling, allowing up to five minute exposures.

With the availability of the monochrome version I could now recommend 
getting one of these as a starter CCD, a pretty good bang for the buck.  
You just have to know the limitations

Andrew


Jeff Hopkins wrote:

>I believe they are using the ICX248AL  chip. You can get  .pdf of the 
>spec sheet at
>
>http://products.sel.sony.com/semi/PDF/ICX248AL.pdf
>
>Meade indicates they are using a 16 bit analog to digital converter, 
>but no details on well depth or dynamic range. still it has got to be 
>a big improvement over the 8 bit units.
>
>Jeff
>
>At 08:54 -0700 4/7/05, Andrew Cooper wrote:
>  
>
>>Pretty good news, fixed color filters really do create problems with
>>astronomical imaging.  A monochome version fixes some of the objections
>>I had against the DSI.  The increase of sensitivity would be correct for
>>getting rid of the on chip color filters.  The 16bit specification is
>>really a bit of marketing fluff, with a Sony CCD they are really getting
>>about 13bits at best, unless binning, then they could theoretically get
>>14bits, it could be much less depending on which CCD they use from the
>>Sony line.  You can't bin with the color version and still get color,
>>you get a poor sensitivity monochrome.
>>
>>Jeff Hopkins wrote:
>>
>>>It looks like Meade has come out with a monochrome version of there
>>>DSI. This will be great for photometry, spectroscopy and for
>>>producing better images. The y claim 2.3 time more sensitivity and 4
>>>times the resolution of the Color DSI. The price is $399 and an RGB
>>>color slide is available for $199 or the combination for $499. That's
>>>the best price I've seen for a 16 bit monochrome CCD.
>>>
>>>Check  http://www.meade.com/dsipro/index.html
>>>
>>>Jeff
>>>      
>>>

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