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Subject: RE: Pictor 416
From: Michael Hart
Reply To: mapug@shore.net
Date: Thu May 16 00:39:32 1996

----------
From: Michael Barber[SMTP:barber@rain.org]
Sent: Wednesday, May 15, 1996 9:05 PM
To: mapug@shore.net
Subject: Re: Pictor 416

Michael Hart wrote:

>Actually the "advertised" performance for the Pictor 416 is under
>1 second for high resolution 768 X 512 (unbinned) images. I suspect
>the 1 second figure is based on theorietical values...SCSI is the
>current speed champ for transferring files greater than
>300K and Meade is rguably the only major CCD supplier using SCSI...

I hope you'll forgive me for butting in...I usually just lurk, but I may
be able to clear up some confusion on this point. I believe the
"transfer" time you're discussing is calculated differently for the
Meade 416 than for the SBIG ST-7 camera. The theoretical transfer time
of 1 sec undoubtedly does not take into account the image digitization
time which must occur before the transfer. The process of digitization
and transfer can be performed in sequence or can be interlaced or
"piped" so that some of the image is digitized and transferred, and
while the transfer is taking place more of the image is digitized, etc.
The ST-7 uses the piped technique via a parallel interface, so it's not
very practical to give a transfer time without including digitization
time. Also, since both digitization and transfer must be completed
after the end of the exposure and before display, transfer time only
without digitization time is a rather meaningless figure. Both times
must be taken into account to know how long you must "wait" to see your
image after the end of the exposure. Since digitization of the image
takes far longer than the transfer, whatever the gain in time of the
SCSI interface, it is not the most significant factor in determining
overall time. I'd be curious to know what the overall time (e.g., from
end of exposure to beginning of display on the monitor) is using the
SCSI interface.

>Meade's competition uses convenient S-L-O-W serial ports (supported
>by the Pictor 416) and somewhat faster parallel ports, I personally
>needed the SCSI solution to my style of imaging- high resolution,
>photographic quality, perfectly centered and focused images. Of
>coarse others may have compelling needs which lead them to non-Meade
>CCD cameras.

Even though it's only "somewhat faster" than "S-L-O-W" <g> the ST-7 with
parallel interface has modes available for focusing (e.g., planet mode)
which will allow image display updates several times a second. Far too
fast to be useful in focusing. Generally, when using the ST-7 in focus
mode we have to intentionally make exposure times longer than one second
(and therefore also the display updates) so we that don't chase
scintillation when we're looking for the best peak values. In this case
SCSI would not be noticed or needed. Otherwise, I think taking
photographic quality, high resolution, nicely centered images has more
to with the user than the interface.

Sorry, don't mean to be argumentative, just wanted to clear up what
looked like a misunderstanding and give another point of view.

Regards,
Michael Barber
SBIG

Michael Barber,

I wrote:

>>I personally
>>needed the SCSI solution to my style of imaging- high resolution,
>>photographic quality, perfectly centered and focused images. Of
>>coarse others may have compelling needs which lead them to non-Meade
>>CCD cameras.

And Michael Barber wrote:

>In this case
>SCSI would not be noticed or needed. Otherwise, I think taking
>photographic quality, high resolution, nicely centered images has more
>to with the user than the interface.

Great comments!

Yes, there is some user preference here, but speed is important, even more
so with your ST-8! Try taking a large image scale eyepiece projection
image of Jupiter at f/28.
Centering is important, so is focusing, but seeing is the variable. The
key is how long does it take to integrate and transfer a 768 X 512 image
perhaps 50 times before you get a "keeper".

Actually, I have great respect for the ST-6, ST-7 & ST-8 as the solution
for many users needs, even some of my own. In fact, I could probably
identify ST-7 benefits YOU may not have thought of! But this is a "Meade"
forum, so I didn't want to offend Meade users with praises for non-Meade
products.

Michael Hart
mhart@netexpress.net

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