Please explain 'Auto Guide Speed' choices.

[Owmuchonomy]

Ey up. I must be being thick this morning.  I've read several times IanL's marvellous sticky and everything Craig Stark has written.  I just can't get my head around why you are given the choice in Synscan to alter your auto guide speed.  I run PHD2 for guiding direct from my Lodestar into the ST4 and use the Synscan handset for everything else.  To be honest i don't think i have major issues with guiding but I can't deal with not understanding why you'd have the option to change your auto guide speed from anything other than 1.0x Sidereal for DSOs. On this forum there are conflicting views (surprise).  Could someone please put the explanation into best North Yorkshire for me.  I would be very grateful.

[xs2man]

I am far from experienced in this, but could it be for tracking planets, and the moon?  They seem to shift across the skies faster than DSO's.

[libraryman]

If you wanted to catch a rabbit, would you want to go to fast and just pass it or too slow and not keep up?

Ideally you would want to keep up with it and just grab it......I see the guide speed in this way and it does depend on your mount,

I don't use the hand set, but eqmod must be the same, most people would sselect 0.3x to 0.5x sidereal.

I'm thick as well, and it does my head in when I can't grasp anything fully.

I hope this does not sound patronising.

Ray

[Owmuchonomy]

I am far from experienced in this, but could it be for tracking planets, and the moon?  They seem to shift across the skies faster than DSO's.

No. There are separate rates such as Lunar for this purpose. I am referring to auto guiding.

[Owmuchonomy]

If you wanted to catch a rabbit, would you want to go to fast and just pass it or too slow and not keep up?

Ideally you would want to keep up with it and just grab it......I see the guide speed in this way and it does depend on your mount,

I don't use the hand set, but eqmod must be the same, most people would sselect 0.3x to 0.5x sidereal.

I'm thick as well, and it does my head in when I can't grasp anything fully.

I hope this does not sound patronising.

Ray

Hi Ray, no not at all patronising but I still don't get it. Craig Stark is quoted as saying don't use anything but 1.0x Sidereal in PHD but plenty of folk do as you say use 0.5 or similar. I just need to understand it then I can either embrace it or dismiss it.

[libraryman]

Hi Chris, in all the recommended info I see, including that from very knowledgeable people i.e. Chris of eq mod, 1.0 x sidereal is considered high!

That said, it is clearly mount / situation specific and very much trial and error... I can't see you being in a position to dismiss all options, lest you do some trials on your setup.

As many people will tell you, if its working ......leave well alone...however I'm not built like that, for me its tuning things that drives me!!!!

As you say; you don't appear to have many issues guiding but understanding what's happening helps to improve things!

Ray

[Thalestris24]

Hi Chris

As I understand it, the autoguide rate is the speed at which the mount responds to corrections issued by PHD or other guiding software. It can be advantageous to have it set below sidereal to more precisely control responses to the corrections. The rate can also be changed in the EQMod expanded panel and there are separate options for RA and DEC. Changing the autoguide rate/speed won't affect the tracking rate which is separate.

Cheers

Louise

[ollypenrice]

I use AstroArt to guide and the guide speed can be fine tuned during guiding. This is very useful because once the software has calibrated the speed at which the scope moves under a guide command you can then lie to it! If the corrections are too much and overshoot you just tell the software that the mount moves faster than it does and the software will then send smaller commands.

Clearly Craig Stark has written PHD for a certain assumed guide speed but other software may be optimised for less. I generally use 0.5x sidereal. 1x seems fast to me. Avalon recommend 0.125x for their belt drives, I think.

Olly

[Owmuchonomy]

I use AstroArt to guide and the guide speed can be fine tuned during guiding. This is very useful because once the software has calibrated the speed at which the scope moves under a guide command you can then lie to it! If the corrections are too much and overshoot you just tell the software that the mount moves faster than it does and the software will then send smaller commands.

Clearly Craig Stark has written PHD for a certain assumed guide speed but other software may be optimised for less. I generally use 0.5x sidereal. 1x seems fast to me. Avalon recommend 0.125x for their belt drives, I think.

Olly

Now then; lying to software.  This approach I like.

[Owmuchonomy]

Thanks all.  

Ray. I will experiment I think.  Looks like my best option.

Louise, yes I get your explanation thanks.  It makes sense to me.

Olly, well now you've got me thinking.  I've just done my Rowan mod and the PHD graph is different for sure especially in response time for corrections.  I get virtually no periodic trend oscillation in the Dec axis.  I think I will try various speeds.  I have resisted getting the Avalon mount but how long I can hang on?

My M51 shot came out OK. 7 min subs and round stars, bloated of course, but round.

[libraryman]

I use AstroArt to guide and the guide speed can be fine tuned during guiding. This is very useful because once the software has calibrated the speed at which the scope moves under a guide command you can then lie to it! If the corrections are too much and overshoot you just tell the software that the mount moves faster than it does and the software will then send smaller commands.

Clearly Craig Stark has written PHD for a certain assumed guide speed but other software may be optimised for less. I generally use 0.5x sidereal. 1x seems fast to me. Avalon recommend 0.125x for their belt drives, I think.

Olly

As far as I am aware, Ascom guiding or pulse guiding through PHD, will allow guide rate changes on the fly.. without recalibration...

Its a very useful feature. I don't think ST4 cable guiding allows this.

Ray

[ollypenrice]

As far as I am aware, Ascom guiding or pulse guiding through PHD, will allow guide rate changes on the fly.. without recalibration...

Its a very useful feature. I don't think ST4 cable guiding allows this.

Ray

Don't know. I use the ST4 system in AA5 and can vary the guide speed but I know nothing about pulse guiding via ASCOM.

Olly

[Owmuchonomy]

If you wanted to catch a rabbit, would you want to go to fast and just pass it or too slow and not keep up?

Ideally you would want to keep up with it and just grab it......I see the guide speed in this way and it does depend on your mount,

I don't use the hand set, but eqmod must be the same, most people would sselect 0.3x to 0.5x sidereal.

I'm thick as well, and it does my head in when I can't grasp anything fully.

I hope this does not sound patronising.

Ray

Just to close the loop,on this one as I still don't really get it, I did some experimentation last night. I was intending doing some imaging but the wispy stuff clung on the upper atmosphere.

So just to recap:

Old HEQ5 pro mount, PHD2 guiding via Lodestar mk 1 with an AA finder guider at 328mm fl. I ran each Synscan autoguide speed for about 10 minutes. The effects on the guide output RMS values were somewhat tangible. 1.0 and 0.75x were dreadful. The default of 0.5 x was pretty good but best results were at 0.25x. 0.125x made no difference. I couldn't qualify this with any decent images due to the cloud cover and it was obvious the system was chasing the seeing a bit. So on a better night I will give that a go.

[IanL]

PHD doesn't know or care about your guiding rate, which is the whole point. The calibration routine measures distance moved over time by monitoring star motion in response to known length guiding pulses. The original version isn't that smart and so you need to recalibrate if changing declination significantly as this affects the rate of star motion in response to guide commands, whereas PHD2 can compensate for declination changes.

The best guide rate for PHD depends on the response of the motors, gears, etc. and will vary by mount. Something less than 0.5x sidereal is usually a good place to start with most mounts. Bear in mind you do have to recalibrate PHD if you change rates significantly. Of course other guiding software can change guide rates on the fly, but requires more knowledge and configuration when first setting up, but clearly time can be saved by not having to calibrate assuming you have the settings right.

[Owmuchonomy]

PHD doesn't know or care about your guiding rate, which is the whole point. The calibration routine measures distance moved over time by monitoring star motion in response to known length guiding pulses. The original version isn't that smart and so you need to recalibrate if changing declination significantly as this affects the rate of star motion in response to guide commands, whereas PHD2 can compensate for declination changes.

The best guide rate for PHD depends on the response of the motors, gears, etc. and will vary by mount. Something less than 0.5x sidereal is usually a good place to start with most mounts. Bear in mind you do have to recalibrate PHD if you change rates significantly. Of course other guiding software can change guide rates on the fly, but requires more knowledge and configuration when first setting up, but clearly time can be saved by not having to calibrate assuming you have the settings right.

Hi Ian, thanks for your input. Much appreciated as always. Yes I'm fully expecting to have to recalibrate as I'm going to use 0.25x tonight and see how it goes. Interesting point about PHD1 vs 2. Your explanation backs up my observation that in PHD1 I was constantly having to tweak the calibration step size based upon target choice. In PHD2 I rarely have to change it at all.