Re: [APML] How to use Pictor 208XT autoguider with Celestar 8 Deluxe?

[Duncan Munro <dmunro@sfu.ca>]

The 208xt should work without a relay box  Meade and Celestron use the 
same pinout on the autoguider port. You should recieve a dual ended RJ12 
cable with the 208xt to connect it directly to your autoguider port. 
However, the 208xt autoguider relays can only be controlled by the CPU 
on-board the 208xt camera head. Meade has  released a simple program 
called "Auoguider" which allows the user to use an external computer to 
focus the 208xt and monitor the calibration and guiding routines of the 
CCD, but you must still use the one button interface on the CCD head to 
set most parameters. The 208xt actually has fairly good stand-alone 
autoguiding abilities and the one button interface is well thought out 
and easy to use.

 Other software, including Pictorview can only use the 208xt to 
autoguide if you have a computer rs232  to telescope interface.You 
CANNOT use a computer to guide with a 208xt through the 208xt on-board 
relays.  For the Celestar this would involve building or buying a relay 
interface to allow your software controlled rs232 port to issue guiding 
commands directly to the drive controller. However, the 208xt is a poor 
choice to use as an autoguider  with a computer as the low speed (56k) 
serial connection and the slow digitization rate, limit  the frame rate 
to about 1 frame every 5 or 6 seconds, even with 2x2 binning and minimal 
sized subframes. Consequently, the maximum correction rate is only about 
once every 7 or 8 seconds. For reasons unknown the on-board CPU can read 
the guiding subframes much more rapidly and can issue guiding commands 
as fast as about 1 per second.

Another caveat is that the 208xt can issue simultaneous movement 
commands in RA and Dec. My CI-700 controller will not allow simultaneous 
movement in both axis, so if the 208xt happens to issue such a command 
one of the drives will not be activated. This can cause problems, which 
might cause the tracking to eventually fail. If you have a precise polar 
alignment there is a good  chance, that the number of simultaneous 
guiding commands will happen infrequently enough, that it won't be a 
problem. IIRC, the Celestar and  the CI-700 share the same controller. 
You can test your controller to see if it will accept simultaneous 
ra/dec commands by looking through a high power EP and pressing an RA 
and Dec button at the same time.

cheers

Duncan

jthirsty@charter.net wrote:

>Hi folks,
>
>Could someone please clarify if/how I can use a Meade Pictor 208XT as an autoguider on a Celestar 8 Deluxe?  I haven't bought the 208 yet, but since it still seems to be available and it's fairly cheap I would like to try it out.  I've been through many web sites, and I'm all confused by just what is involved.
>
>Question 1: Can I use this combination, or do Meade and Celestron try to prevent cross-compatibility?
>
>Question 2: How would I hook it up?  My hand controller has an RJ12 port on the top labeled "Autoguide", so can I just connect the CCD cable to this port, or do I need a relay box, or is the pin-out different between them?  Then do I just connect the serial cable to the laptop and use Pictorview? If so, then presumably the laptop calculates the corrections, which are then transmitted to the 208 which then relays them to the hand controller, right?
>
>I hope I'm not wasting anybodys time with something that would be obvious if I just bought the darn thing, but I've been reading about optocouplers and webcam mods and relay boxes and software for 3 days now and am pretty much confused.
>
>thanks,
>Jerry Thirsty
>
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