guiding via ST-4 or Ascom interface ?

[glowingturnip]

I got a new QHY5LiiC recently, and was experimenting with guiding via ST-4 (ie 'on-camera' in PHD, with the ST-4 cable straight from the camera to the autoguider port on the mount) versus the Ascom driver connection I usually do (USB on laptop via RS232-USB interface, plugged in to the synscan handset).  My GOTO is an after-market Synscan kit on a CG4 mount.

Initial findings were that with the same calibration step in PHD, the mount with an ST4 connection would move much less in RA and hardly at all in Dec compared to with the ASCOM connection, such that I couldn't really use it at the time, and went back to the ascom method.  I was wondering if that's due to an autoguide speed setting - the mount just has one autoguide speed setting for both RA and Dec, and was 0.5x.  I couldn't find any way of getting into the camera settings to see if there is any speed setting there.

Reading around, it seems to be an accepted opinion that the Ascom link has a time lag.  However, reading through the PHD faq I found somewhere though suggests that the only problem with Ascom is if your mount doesn't accept pulseguiding (ie with pulseguiding, the mount receives a single command, say 'move East for 100mS' which it knows how to execute - but without pulseguiding, PHD has to send two commands, one saying 'move East' and the next sent 100mS later saying 'stop', but if the mount doesn't poll for and act on both commands immediately, the time period of the pulse can be mucked up).  I'm not sure whether my mount has pulseguiding or not though.  Also not sure if the USB/RS232 would introduce any lags or not.

(Seems that on the other hand, using Ascom can help with calibration when PHD knows your declination, and helps with flipping as it knows which side of the pier you are)

So any thoughts as to which is better, ST4 or Ascom, and any ideas why I was getting such small moves with ST4 ?

Cheers

[Thalestris24]

Hi

As I understand it, it shouldn't make any difference whether you use either pulse guiding or ST4 guiding - either will achieve what you want. Your ST4 issue could have been caused by a faulty electronics, faulty cable, software problem or some combination. I've only ever used pulse guiding myself as I have a Synta mount and am running eqmod on my PC so have the usb to serial cable anyway.

Louise

[chrisshillito]

Reading around, it seems to be an accepted opinion that the Ascom link has a time lag.  However, reading through the PHD faq I found somewhere though suggests that the only problem with Ascom is if your mount doesn't accept pulseguiding (ie with pulseguiding, the mount receives a single command, say 'move East for 100mS' which it knows how to execute - but without pulseguiding, PHD has to send two commands, one saying 'move East' and the next sent 100mS later saying 'stop', but if the mount doesn't poll for and act on both commands immediately, the time period of the pulse can be mucked up).

PHD may just send one command to an ascom driver but the driver itself may need to send multiple commands to the mount to implement that pulse (EQMOD for instance sends two commands - one to change the tracking rate and one to return it to sidereal at the end of the 'pulse'). So the PHD FAQ isn't really giving you a complete answer, and in truth it can't as different hardware and drivers do things differently. 

With both ST-4 and Pulse guiding communications are required to initiate the guiding correction - In the case of ST-4 PHD commands the camera to pulse its ST-4 outputs whilst with Pulse Guiding PHD uses the ASCOM driver to command the mount directly to either move or change its tracking rate (again diferent drivers take different approaches). A possible advantage of ST-4 is that the camera hardware/firmware is designed specifically with the purpose of driving ST-4 interface in real time and so the timing of the pulse can potentially be performed much more accurately could ever be achieved  by a  driver operating under windows.

Whilst both systems have their inbuilt communication lags etc. these really aren't worth worrying about as they pale into insignificance when compared time taken for guide image acquisition and processing - use a guide expose of 2 seconds and you've introduced at least a 2 second lag in your control system!

In reality there is very little difference between ST4 and pulse guiding performance - excellent results have been achieved with both, and very poor results have been obtained with both also! In both cases you will need to tune the guiding parameters to your specific equipment and maybe even target - settings that work well with ST-4 may not work so well with pulse guiding .

Chris.

[glowingturnip]

thanks both, that confirms what I thought.  I have been getting decent results with ascom, so I guess I'll stick with that, just wanted to make sure I wasn't missing a trick not using ST4.

[Gerry Casa Christiana]

Hello I know I'm reopening a old thread. Can I just ask a question. I'm using ST-4 but I want to be using ascom but how do I set that up? I use EQMOD (brilliant) and PHD2 so apart from unplugging the cable from my mount where do I set up the options to do ascom pulse guiding. I have a eq6 with a ASI120mm as my guide camera which has a dedicated ST-4 port. I'd like to try it tonight. 

Thanks! 

 

Gerry

[wimvb]

Try mount control in phd2. It should be an option at the very startup of phd, when you're asked to connect to camera and mount. ST4 is the 'on camera' option for mount control, while pulse guiding needs a specified mount (ascom compatible).

[Cornelius Varley]

In PHD2, select the camera type and select Eqmod Ascom HEQ5 /6 for the mount. Press the mount setup button next to the mount list which will bring up the Eqmod ascom setup window. Select "Ascom pulseguiding" for the autoguiding option.

[Gerry Casa Christiana]

Thanks a lot people I'll try that. 

 

Gerry

[Greenleaf27]

On 28/08/2014 at 16:57, glowingturnip said:

I got a new QHY5LiiC recently, and was experimenting with guiding via ST-4 (ie 'on-camera' in PHD, with the ST-4 cable straight from the camera to the autoguider port on the mount) versus the Ascom driver connection I usually do (USB on laptop via RS232-USB interface, plugged in to the synscan handset).  My GOTO is an after-market Synscan kit on a CG4 mount.

Initial findings were that with the same calibration step in PHD, the mount with an ST4 connection would move much less in RA and hardly at all in Dec compared to with the ASCOM connection, such that I couldn't really use it at the time, and went back to the ascom method.  I was wondering if that's due to an autoguide speed setting - the mount just has one autoguide speed setting for both RA and Dec, and was 0.5x.  I couldn't find any way of getting into the camera settings to see if there is any speed setting there.

Reading around, it seems to be an accepted opinion that the Ascom link has a time lag.  However, reading through the PHD faq I found somewhere though suggests that the only problem with Ascom is if your mount doesn't accept pulseguiding (ie with pulseguiding, the mount receives a single command, say 'move East for 100mS' which it knows how to execute - but without pulseguiding, PHD has to send two commands, one saying 'move East' and the next sent 100mS later saying 'stop', but if the mount doesn't poll for and act on both commands immediately, the time period of the pulse can be mucked up).  I'm not sure whether my mount has pulseguiding or not though.  Also not sure if the USB/RS232 would introduce any lags or not.

(Seems that on the other hand, using Ascom can help with calibration when PHD knows your declination, and helps with flipping as it knows which side of the pier you are)

So any thoughts as to which is better, ST4 or Ascom, and any ideas why I was getting such small moves with ST4 ?

Cheers

But if you go for PHD guiding, what software you use for capturing images

Like for ASCOM interface there is SGP which basically eliminates the hassle

Is there any similar software for capturing via PHD guiding?

[alacant]

9 hours ago, Greenleaf27 said:

But if you go for PHD guiding, what software you use for capturing images

Hi. I use PHD2 and APT. Does SGP do both? 

[glowingturnip]

On 7/21/2017 at 08:34, Greenleaf27 said:

But if you go for PHD guiding, what software you use for capturing images

Like for ASCOM interface there is SGP which basically eliminates the hassle

Is there any similar software for capturing via PHD guiding?

that was a very old quote of mine  :-)

these days though, I'm using PHD2 with the QHY with on-camera ST4 to control the mount, and using SGP to control the CCD.  There's a proper ASCOM driver for the Skywatcher mounts now (not EQMOD) so I've got SGP plate-solving for me like a breeze.

SGP does not have an inbuilt guider, but works very well with PHD.