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Date: 07 Sep 2006 23:49:28
From: Pierre Vandevennne
Subject: guiding relays vs scope controls
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I seem to have problems with the autoguiding relays of my sbig camera.
Haven't really objectivated the issue but it shows up with two different
mounts using two different cables, so I guess there not much room for
doubt.
I have therefore switched my guiding from guider relays to telescope
control. Is the performance going to be markedly different? So far,
everything is fine, but I am using a very short focal length (540mm) and
have had to cut the aggressivness in half, all other things being equal.
Pierre
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Date: 08 Sep 2006 03:25:19
From: Chris L Peterson
Subject: Re: guiding relays vs scope controls
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On 07 Sep 2006 23:49:28 GMT, Pierre Vandevennne
<pierre@datarescue_ns.com > wrote:
>I seem to have problems with the autoguiding relays of my sbig camera.
>Haven't really objectivated the issue but it shows up with two different
>mounts using two different cables, so I guess there not much room for
>doubt.
>
>I have therefore switched my guiding from guider relays to telescope
>control. Is the performance going to be markedly different? So far,
>everything is fine, but I am using a very short focal length (540mm) and
>have had to cut the aggressivness in half, all other things being equal.
There are two ways the guider logic can work. The "bad" way, which is
very common, is that the guider software sends a command to start a
correction, and then after some amount of time it sends another command
to stop it. The reason this can be bad is because Windows is not a
realtime operating system, and the timing between the two commands can
end up quite different from what the guide correction duration should
actually be. Another problem is that the commands can get fragmented
during transmission, creating a timing error. This is particularly
possible if the transmission interface is networked: Ethernet or USB
(including serial over either of these).
The "good" way of sending guide commands is to send a single command
containing the direction and the time. This can't get fragmented, and
isn't dependent on Windows for timing. Newer mounts increasingly have
this type of guiding built into their interface.
AFAIK, SBIG cameras don't manage guider timing internally. That means
that they use the first sort of control, with all its possibilities for
error. Whether you will do better using scope control depends on whether
your mount supports internally timed guiding. If it does, your
performance may be better. Otherwise, it should be pretty much the same
either way.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 08 Sep 2006 02:14:01
From: William R. Mattil
Subject: Re: guiding relays vs scope controls
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Pierre Vandevennne wrote:
> I seem to have problems with the autoguiding relays of my sbig camera.
> Haven't really objectivated the issue but it shows up with two different
> mounts using two different cables, so I guess there not much room for
> doubt.
>
> I have therefore switched my guiding from guider relays to telescope
> control. Is the performance going to be markedly different? So far,
> everything is fine, but I am using a very short focal length (540mm) and
> have had to cut the aggressivness in half, all other things being equal.
>
> Pierre
You'd probably getting more response to this on the SBIG list. And the
only SBIG cameras that use relays are the ST-4 and STV. So I suspect
that "guider relay" is a Maxim DL term ?
Bill
--
William R. Mattil : http://www.celestial-images.com
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Date: 08 Sep 2006 02:30:12
From: Pierre Vandevennne
Subject: Re: guiding relays vs scope controls
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"William R. Mattil" <wrmattil@ix.netcom.com > wrote in
news:Jl4Mg.26291$gY6.17667@newssvr11.news.prodigy.com:
> You'd probably getting more response to this on the SBIG list.
True, but I thought putting some actual amateur astronomy question here
couldn't hurt :-)
> And the
> only SBIG cameras that use relays are the ST-4 and STV. So I suspect
> that "guider relay" is a Maxim DL term ?
Well, I have two ways to guide with the ST-2000XM / Maxim combo: one is
throught the RJ11 guide cables and ports, both on my Vixen Atlux through
the Skysensor and on the HEQ5 (with their respective appropriate cables of
course), the second method goes through the PC serial port and has Maxim
send commands to the go-to hand controller.
I've already had problems with the guiding port on the SBIG two years ago,
which I fixed with a soldering iron and a small logic analyzer :-) and that
is probably the same issue again (a short circuit). But if the direct scope
control is as good and the guiding port, maybe I'll just save the trouble.
Yes, I know I could find out by trying different configs, but we have so
few good nights around here that I do not want to sacrifice them to tests.
--
Pierre
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Date: 08 Sep 2006 05:15:21
From:
Subject: Re: guiding relays vs scope controls
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>>The reason this can be bad is because Windows is not a
realtime operating system, and the timing between the two commands can
end up quite different from what the guide correction duration should
actually be. Another problem is that the commands can get fragmented
during transmission, creating a timing error. This is particularly <<
This is very interesting and explains some of my observations.
With the ST-4 I use a very old Compact laptop (about 15 yrs old) in
the DOS mode with CCDTrack. I never had any problems. Ive tried newer
laptops in the Windows mode and coulden't get any performance
reliability.
Chris L Peterson wrote:
> On 07 Sep 2006 23:49:28 GMT, Pierre Vandevennne
> <pierre@datarescue_ns.com> wrote:
>
> >I seem to have problems with the autoguiding relays of my sbig camera.
> >Haven't really objectivated the issue but it shows up with two different
> >mounts using two different cables, so I guess there not much room for
> >doubt.
> >
> >I have therefore switched my guiding from guider relays to telescope
> >control. Is the performance going to be markedly different? So far,
> >everything is fine, but I am using a very short focal length (540mm) and
> >have had to cut the aggressivness in half, all other things being equal.
>
> There are two ways the guider logic can work. The "bad" way, which is
> very common, is that the guider software sends a command to start a
> correction, and then after some amount of time it sends another command
> to stop it. The reason this can be bad is because Windows is not a
> realtime operating system, and the timing between the two commands can
> end up quite different from what the guide correction duration should
> actually be. Another problem is that the commands can get fragmented
> during transmission, creating a timing error. This is particularly
> possible if the transmission interface is networked: Ethernet or USB
> (including serial over either of these).
>
> The "good" way of sending guide commands is to send a single command
> containing the direction and the time. This can't get fragmented, and
> isn't dependent on Windows for timing. Newer mounts increasingly have
> this type of guiding built into their interface.
>
> AFAIK, SBIG cameras don't manage guider timing internally. That means
> that they use the first sort of control, with all its possibilities for
> error. Whether you will do better using scope control depends on whether
> your mount supports internally timed guiding. If it does, your
> performance may be better. Otherwise, it should be pretty much the same
> either way.
>
> _________________________________________________
>
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
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Date: 08 Sep 2006 08:28:19
From: Roger Hamlett
Subject: Re: guiding relays vs scope controls
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"Pierre Vandevennne" <pierre@datarescue_ns.com > wrote in message
news:Xns9838128D0648Epierredatarescue@195.238.0.34...
>I seem to have problems with the autoguiding relays of my sbig camera.
> Haven't really objectivated the issue but it shows up with two different
> mounts using two different cables, so I guess there not much room for
> doubt.
>
> I have therefore switched my guiding from guider relays to telescope
> control. Is the performance going to be markedly different? So far,
> everything is fine, but I am using a very short focal length (540mm) and
> have had to cut the aggressivness in half, all other things being equal.
How 'good' software guiding is, depends largely on your mount controller.
'Relay' guiding (actually only a real 'relay' on the ST4, and similar
guiders, while on the SBIG cameras a 'pull down' transistor), gives less
'latency' (the mount is being controlled almost immediately, instead of
having to wait for a longer serial command). How long the latency for
serial guiding is, depends on the 'command set' of your mount. The
original LX200, had a 'reasonable' nudge command. The latter GPS units,
dropped this, and for a while gave poor responses, and then an
'undocumented' nudge command in a slightly different form was found, and
now the control is generally good. Similarly, some other makes of scope,
have better or worse nudge/move commands, with varying degrees of quality,
and in some cases, a much slower 'move' command has to be used, often with
relatively slow response, and poor accuracy. As another example, the Vixen
SS2K, 'rounds' the position numbers fed from a serial command, and you
cannot actually nudge to the resolution of the controller, with the serial
control. However for shorter focal length scopes, both still work OK on
this mount, and this only gives problems at high image scales.
Though you have the system working, you do really need to find out what is
wrong with the direct control. A number of questions/comments apply.
First, some mounts need to be in the right 'mode' to respond to the guider
input. For example, the Gemini controller, ignores the guide input, unless
the controller is in 'photo', or 'all speeds' mode. Then check the actual
pinout on the cable. Different cables are needed for some mounts (the
Vixen SS2K, for example, does require a custom cable). Also some
controllers do actually require a relay, or opto-coupler (on the Losmandy
Gemini for example, the 'older' version, with telephone style motor
connectors, requires the guider pins to be pulled 'up', not 'down' as the
SBIG camera generates - this requires a relay adaper to work, and
connecting without this, can damage the controller or camera). Also note
that the correct cable, is normally a 'crossover' cable (pin1 to pin6),
not a straight through cable.
Best Wishes
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Date: 08 Sep 2006 14:00:00
From: Chris L Peterson
Subject: Re: guiding relays vs scope controls
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On Fri, 08 Sep 2006 08:28:19 GMT, "Roger Hamlett"
<rogerspamignored@ttelmah.demon.co.uk > wrote:
>How 'good' software guiding is, depends largely on your mount controller.
>'Relay' guiding (actually only a real 'relay' on the ST4, and similar
>guiders, while on the SBIG cameras a 'pull down' transistor), gives less
>'latency' (the mount is being controlled almost immediately, instead of
>having to wait for a longer serial command)...
I don't think latency is a significant factor, for two reasons. First,
the latency shouldn't be significantly different for a relay controller
versus direct telescope control, since the relay controller itself is
receiving a command string itself before it can interpret and act on it.
But more important is the fact that the latencies are small compared
with the guide camera integration and readout time. The former is on the
order of milliseconds, the latter on the order of seconds.
Precisely _when_ you issue your correction command is less important
than its _duration_; a few milliseconds error in duration is much more
significant than a few milliseconds of latency.
I have moderate latency in my guiding because the commands are sent via
Ethernet, and can be delayed by the protocol (which may delay
transmission somewhat in an effort to construct a more efficient
packet). Back when I used a start/stop guider protocol, guiding over the
network caused me all sorts of problems. Once I switched to a
guide-by-time protocol, all the problems disappeared, in spite of the
fact that the latency is still there.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 08 Sep 2006 21:05:50
From: Roger Hamlett
Subject: Re: guiding relays vs scope controls
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"Chris L Peterson" <clp@alumni.caltech.edu > wrote in message
news:2et2g29an7hi02c187vj4e8vpja8t0utdp@4ax.com...
> On Fri, 08 Sep 2006 08:28:19 GMT, "Roger Hamlett"
> <rogerspamignored@ttelmah.demon.co.uk> wrote:
>
>>How 'good' software guiding is, depends largely on your mount
>>controller.
>>'Relay' guiding (actually only a real 'relay' on the ST4, and similar
>>guiders, while on the SBIG cameras a 'pull down' transistor), gives less
>>'latency' (the mount is being controlled almost immediately, instead of
>>having to wait for a longer serial command)...
>
> I don't think latency is a significant factor, for two reasons. First,
> the latency shouldn't be significantly different for a relay controller
> versus direct telescope control, since the relay controller itself is
> receiving a command string itself before it can interpret and act on it.
> But more important is the fact that the latencies are small compared
> with the guide camera integration and readout time. The former is on the
> order of milliseconds, the latter on the order of seconds.
>
> Precisely _when_ you issue your correction command is less important
> than its _duration_; a few milliseconds error in duration is much more
> significant than a few milliseconds of latency.
>
> I have moderate latency in my guiding because the commands are sent via
> Ethernet, and can be delayed by the protocol (which may delay
> transmission somewhat in an effort to construct a more efficient
> packet). Back when I used a start/stop guider protocol, guiding over the
> network caused me all sorts of problems. Once I switched to a
> guide-by-time protocol, all the problems disappeared, in spite of the
> fact that the latency is still there.
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. I have seen a unit, where when using
serial commands, despite it having what appeared to be a working
'milli-second nudge' command - which is the ideal guiding command, there
was a delay nearer to perhaps 1/3rd second, between receiving the serial
command, and moving!. I have used serial guiding fine, on many scopes, but
there can be a 'caveat' on some units. the 'longer serial command', is not
just the time taken to actually send the data, but the time for the
controller to interpret/respond to it.
Best Wishes
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Date: 08 Sep 2006 21:40:03
From: Chris L Peterson
Subject: Re: guiding relays vs scope controls
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On Fri, 08 Sep 2006 21:05:50 GMT, "Roger Hamlett"
<rogerspamignored@ttelmah.demon.co.uk > 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?
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 09 Sep 2006 19:00:47
From: Roger Hamlett
Subject: Re: guiding relays vs scope controls
|
"Chris L Peterson" <clp@alumni.caltech.edu > wrote in message
news:0ko3g2hlteejm5ahf9bor5b50bgnn3h38c@4ax.com...
> On Fri, 08 Sep 2006 21:05:50 GMT, "Roger Hamlett"
> <rogerspamignored@ttelmah.demon.co.uk> 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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Date: 08 Sep 2006 21:24:07
From: Pierre Vandevennne
Subject: Re: guiding relays vs scope controls
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"Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk > wrote in
news:OWkMg.16332$G72.14221@newsfe3-gui.ntli.net:
> command, there was a delay nearer to perhaps 1/3rd second, between
> receiving the serial command, and moving!. I have used serial guiding
> fine, on many scopes, but there can be a 'caveat' on some units. the
> 'longer serial command', is not just the time taken to actually send
> the data, but the time for the controller to interpret/respond to it.
That's what I fear and what I guess I'll have to check with a longer focal
length. Thanks for the very detailed first answer Roger.
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Date: 08 Sep 2006 13:27:00
From: RMOLLISE
Subject: Re: guiding relays vs scope controls
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Hi:
Are you really using "relays," or do you just mean you're running from
the guiding output of an SBIG camera to an SBIG compatible guide port
on a scope?
The alternative to the SBIG setup is to use a camera and a guide
program that offers RS-232 guiding. Most folks report zero difference
once everything (USB serial adapters, etc.) are set-up and working
properly.
Peace,
Rod Mollise
Author of:
Choosing and Using a Schmidt Cassegrain Telescope
and
The Urban Astronomer's Guide
<http://skywatch.brainiac.com/astroland >
Pierre Vandevennne wrote:
> I seem to have problems with the autoguiding relays of my sbig camera.
> Haven't really objectivated the issue but it shows up with two different
> mounts using two different cables, so I guess there not much room for
> doubt.
>
> I have therefore switched my guiding from guider relays to telescope
> control. Is the performance going to be markedly different? So far,
> everything is fine, but I am using a very short focal length (540mm) and
> have had to cut the aggressivness in half, all other things being equal.
>
> Pierre
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Date: 08 Sep 2006 21:16:19
From: Pierre Vandevennne
Subject: Re: guiding relays vs scope controls
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"RMOLLISE" <rmollise@hotmail.com > wrote in news:1157747220.303781.167430
@m79g2000cwm.googlegroups.com:
> Are you really using "relays," or do you just mean you're running from
> the guiding output of an SBIG camera to an SBIG compatible guide port
> on a scope?
Yes, I am aware of the difference (I also own a ST4) but I was just using
Maxim's terminology
I was running the following setup
ST2000XM guide port - > skysensor guide port (to atlux) with a custom cable
that has been working for a couple of years
ST2000XM guide port - > HEQ5 Pro guide port, with the bundled SBIG cable.
That's the setup that doesn't work at all
> The alternative to the SBIG setup is to use a camera and a guide
> program that offers RS-232 guiding. Most folks report zero difference
> once everything (USB serial adapters, etc.) are set-up and working
> properly.
Yup, and that is the setup I am now on. I wondered if there was any
difference, good or bad. Your feedback reassures me! Thanks
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