Re: guiding relays vs scope controls


"Chris L Peterson" <clp@xxxxxxxxxxxxxxxxxx> wrote in message
news:0ko3g2hlteejm5ahf9bor5b50bgnn3h38c@xxxxxxxxxx
On Fri, 08 Sep 2006 21:05:50 GMT, "Roger Hamlett"
<rogerspamignored@xxxxxxxxxxxxxxxxxxx> wrote:

I have to disagree slightly.
You are thinking about the communication latencies only. These are
generally small. However some mounts seem to have a significant 'command
latency' on the serial commands...

That's not good. Happily I've never seen that particular problem on any
of my setups (certainly, LX200s both classic and GPS respond very fast
to serial commands).

All the same, I don't think that should present a problem for guiding
(even at 1/3 second) unless you are using on/off command sequences, and
the latency is variable. Is that what you've seen?
I have actually seen two seperate problems, which gave similar behaviours.
The first was with the Vixen SS2K. This would at high image scales, seem
not to respond to a number of guide commands, and then suddenly move quite
a noticeable amount. I tracked this down by trying the experiment of
adding a serial tracker, watching the guide command issued, and then
reading back the scope position. It turned out that scope ignored small
commands, with the amount 'ignored', varying according to the actual
numbers involved. I queried this with Vixen and they replied that the
controller, did do exactly this, rounding the numbers it was given to an
internal format. In fact it caused little problems at reasonable image
scales, but at the high image scale I was using, gave troubles. On this
the guide port solved the problem. The other system, was an early release
of the Losmandy Gemini, which experienced the strange 'delay', only when
dealing with some numbers (I suspect this was an arithmetic problem in the
conversion between the external and internal numeric formats. This was
fixed in the next software release. Seperately, not as a 'latency'
problem, I have also seen an issue with the AP900, and the ASCOM driver,
which does so much I/O, that it can cause a system bottleneck. I have
taken to disabling serial scope I/O when guiding (just using the guide
port), as otherwise you get line artefacts on image downloads. This with a
3.2GHz machine with 1.5GB RAM, doing nothing but scope control and
imaging...

Best Wishes


.

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