William D. Carroll wrote:

> correct, but you don't need to buffer the whole image in the camera to
> to that. and that is my point.
> You do it now with a parallel port camera. you can do the same
> over USB. the camera can only be clocked so fast anyway and if you do it at
> to high a speed you introduce noise from reading the image.
>
> weither you use USB,10BaseT or SCSI you still read it out at a speed that
> gets it as quickly as possible but not so fast you introduce noise.
>
>
>
> -----Original Message-----
> John Oliver
> Sent: Wednesday, April 25, 2001 8:49 PM
> Subject: Re: [M]: Any CCD with USB Interface?
>
>
> William D. Carroll wrote:
>
>
>> actually there is no reason you need a full frame buffer inside the camera
>> you could send data as it's pulled off the camera.
>>
>> You just need a dedicated micro to clock the camera and interpret commands
>> then to send the data as read over the Ethernet link
>>
>> DOug
>
> Unless the chip is clocked out at a constant rate, the dark current
> varies from row to row. I know of no circumstances in which one can
> count on reading out 1000 rows of a CCD with no interruptions. What am I
> missing?
> --
> John Oliver

With parallel port or USB the local CPU is in control of the clocking
out and can do so at a regular rate. If one goes to ethernet and one
does not buffer the entire image, then the clocking out depends on net
traffic between the remote CPU and the CCD. If I am in Florida and my
CCD is on the GTC in the Canary Islands (an actual case since UF is now
a partner in that 10.4m telescope) I can not be certain that I will be
able to clock that CCD out at a uniform rate. I still see no way of
avoiding local buffering.
--
John Oliver
Department of Astronomy
University of Florida
Associate Chairman
Undergraduate Coordinator

Netscape Champion

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