Connecting Guide Camera to ST4 VS Laptop

[Ali7]

Hi, Which option would improve telescope guiding: connecting guide Camera to ST4 port or to the laptop?
Thanks

[Merlin66]

Ali,
More info needed.
What guide camera?
What mounting?
What guide software do you have/ use?

[Ali7]

Guide camera Zwo 120mm mini, mount HEQ5 Pro, software that I'm planning to use for guiding is PHD.

[Merlin66]

OK,
If you connect the guide camera to the laptop, what connects the laptop to the mount?
Your HEQ5 pro can be connected using ASCOM/ EQMod and a EQDir cable.
This would then allow you to use pulse guiding with PHD2 (via EQMod)
Is this what you have in mind?

I use an HEQ5pro with various guide cameras and still happy to use the ST-4 direct connection from the guide camera.....

[Ali7]

"If you connect the guide camera to the laptop, what connects the laptop to the mount?" - at this stage, I don't have a cable, hence I'm asking if I keep using the ST4 connection or connect the laptop to the mount using a cable, will this improve guiding ?

[Merlin66]

OK
I think the question you're trying to ask is:
"Is pulse guiding better than direct ST-4 guiding?"
The jury is divided...some say yes, some say no....
I stick with the ST-4 cable because it works for me.

[The_bluester]

The advantages I see of EQMOD and pulse guiding is that you can control the mount from your laptop and a lot of imaging software, and flowing on from that is the ability to have PHD2 connect via EQMOD and get pointing information from the mount, so you can calibrate the guiding and not need to recalibrate for a pointing change or meridian flip, only if you change telescope or guide camera angle with respect to the sky. I usually go for weeks between PHD calibration runs.

[Startrek]

Ali
The current developers of PHD2 , Bruce Waddington and Andy Galasso recommend direct pulse guiding instead of ST4 and so do many other experienced astrophotographers. It’s the most reliable and efficient way to connect and run PHD2
I started with direct pulse guiding with my HEQ5, 50mm guide scope and ZWOASI120MM-3 and have not had an issue in 3 years of guiding
Note: Do not use a ZWOASI120MM USB2 Guide Camera with PHD2 !!!! There is an inherent bug in the driver and will connect sometimes and other times won’t
Use the USB3 version of the ZWOASI120MM if you choose this camera range and you won’t have any issue. I even use a USB2 cable to connect the USB3 camera to the laptop , no issues at all.
Like others have mentioned, if your mount is connected to the laptop and controlled with EQMOD via a shoestring EQ direct cable or wifi etc.. PHD2 just uses this connection to see and control the mount through Ascom. Once the guide camera is connected to the laptop, PHD2 can initiate calibration and commence guiding
I put together two short lists of procedures and tips on PHD2 guiding a while back.Let me know if want me to send them
Cheers

[Astronut07]

Martin

I would also be interested in any information you may have regarding setting up PHD2 pulse guidance


Cheers
Ben

[Merlin66]

Paul,
You can get positional feedback to PHD when using the ST-4 connection, just add your mount details to the “AUX mount” panel.

[Startrek]

Ali and Ben,

PHD2 pulse guiding direct from EQ mount to laptop requires Ascom based PHD2 compatible Goto , acquisition and or capture software like EQMOD , APT , SGP etc.... either direct EQ connect or wifi connect to mount and a separate USB cable from guide camera to laptop.
To install PHD2 including camera drivers , cameras , cabling and general information to get started , please refer to the latest PHD2 manual which comes with the software
Below are some general procedures and tips to assist with PHD2 guiding -

PHD2 Set Up and Guiding tips

1/ Try to Polar align to around 1arc minute error on Alt and Az

2/ “Auto select guide star” (recommended by PHD2) or manually select star that’s not too bright or saturated to avoid lost stars

3/ If guiding is poor ( above 2 arc seconds ) utilise the Guiding Assistant

4/ Check and adjust focus of your guide scope and camera to minimise lost stars

5/ Set your guide camera exposure time between 2 and 4 seconds ( Looping ) 2 seconds is a good starting point

6/ The SNR value of the guide star should be between 15.0 and 40.0 to avoid losing the guide star

7/ Don’t over correct settings , under correcting will let you manage your guiding performance better

8/ If Guiding is poor try and keep your min mo above 0.25 in RA and DEC . Don’t go above 0.6. A good starting point for min mo is 0.20 or 0.25

9/ Important- Build a Dark Frame library and a Bad pixel map to provide good calibration and stable guide star. PHD2 will only allow you to use one or the other

10/ The RA Osc value should be between 0.3 to 0.5
If it drops to 0.1 or lower then increase the RA aggressiveness or decrease the hysteresis
If it gets quite high say 0.8 then reduce the RA aggressiveness or increase the hysteresis

11/ Use Ascom Guiding - Laptop direct connect to mount ( preferred by PHD2 Developers) in lieu of ST4 connected guiding via camera to mount

12/ USB 2 cable to camera is not to exceed 5 metres

13/ Try and avoid cabling through a hub even a Powered hub, direct connect to the computer , you will have less issues

14/ Ensure you have the latest driver installed for your guide camera

15/ If guide camera is USB2 make sure you connect into a USB2 port with USB2 cable
If the guide camera is USB3 it most probably will connect with a USB2 cable

16/ Ensure you enter all the correct data for your guide camera into PHD2 brain tabs

17/ Make sure you get good Calibration. Calibrate within 10deg of celestial equator and within an hour of meridian
Once Calibrated save it and reuse it ( go to Brain in guiding tab and tick box “Auto restore Calibration”)

18/ if you lose guide star often , go to Brain in guiding tab and increase “Search region” and increase “ Star mass detection”



PHD2 Extra Guiding Tips
1/Try and keep your min mo in RA and Dec just above your arc sec error in both axis or leave as default (0.20) and see how the guiding performs over a few minutes
2/ Only make small adjustments in RA and Dec Aggressiveness. Wait for guiding to run for a few minutes to see any change or improvements
3/ If guiding is saw toothing in RA ( blue ) badly you maybe over correcting , reduce RA Aggressiveness and increase Min mo in RA only
4/ If guiding is saw toothing badly in DEC (red) then you could be over correcting, reduce DEC Aggressiveness and increase Min Mo in DEC
5/ If DEC ( red ) is staying for the most part above or below the centre line you are under correcting , so increase DEC Aggressiveness a bit and reduce Min mo
6/ If RA (blue) is receiving 2 or more consecutive pulses to correct it , then RA Aggressiveness is to low so increase by 5 at a time over a while to monitor its performance
7/ A random big spike in RA ( blue ) could be caused by many things like cable snag or drag , gust of wind , slight bump of the tripod , loose equipment or lost Guide Star
8/ A big random downward spike in DEC (red) can be caused by a “dither” command from your capture software through PHD2 , but you should see the word “dither” above the spike area on the PHD2 graph
9/ If guiding is still bad , go to the Brain and change the Guiding Algorithm from Hysterisis to “Predictive PEC”
It usually takes 20minutes of guiding on this algorithm to run 2 worm cycles of the mount and allow PEC training of the mounts performance. Sometimes the mount performs better using this PEC algorithm
10/ You can also try the Guiding Assistant which will make suggestions after letting the mount track after a test period of 2 minutes
11/ Only use the Backlash Compensation setting If Guiding Assistant advises to do so.
Go to Brain then Algorithms
Use only if your backlash value from the Guiding Assistant is 3 seconds or less or if the Guiding Assistance says to use this function


Advanced Functions for PHD2 - Predictive PEC ( Periodic Error Correction) in PHD2

PPEC is an alternative to the Hysteresis algorithm normally used for your mounts RA guide corrections and can provide improvements to your mounts overall guiding
Go to Brain
Select Algorithms
In ‘Right Ascension’ select “Predictive PEC”
Use all default settings for Predictive Weight, Reactive Weight and Min Move ( Period Length can be adjusted to suit your mounts worm cycle period but always leave “Auto Adjust Period” checked or ticked )
Do your normal Calibration then start guiding
PPEC takes time to train itself and perform
It starts out using the normal RA Hysteresis algorithm then shifts seamlessly to the PPEC algorithm after about 2 worm cycles of the mount when it learns the mounts performance
HEQ5 mount worm cycle period is 638 sec or 10 minutes 38 seconds
EQ6-R mount worm cycle period is about 480 sec or 8 minutes
PPEC will remain whilst guiding , stopping and starting guiding for focusing and dithering on the same target
If you stop and slew to a new target , PPEC must be turned off and then on again , start guiding and then re train itself again on the new target
Once training is complete after 2 worm cycles, the PPEC algorithm uses both reactive and predictive guide corrections which in principle is usually more accurate than just Hysteresis on its own
EQMOD has a feature to store your mounts PEC curve which is created by a third part software like PECprep and allows PHD2 to retain and use this data when running the PPEC algorithm. This saves PHD2 time when setting up and guiding for the next imaging session
The mounts Synscan handcontroller also has a function to record PEC and store it in the mount for PHD2 to use along side the PPEC function

[The_bluester]

Thanks Ken, to be honest I never looked into it as I went straight to pulse guiding, in the case of the EQ5/6 when you have an EQdirect cable there was not much point adding an extra cable to duplicate something the first could already do. I have been told the Tak Temma NJP does better with ST4 guiding though.

[Merlin66]

Paul,
You’d still need to add a USB connection from the guide camera to the PC?
Seems easier to have the guide cable between the camera and the mount.....

[The_bluester]

Originally I had a USB cable to the guider from the PC (Which is needed anyway to controlthe guide cam) but as things stand with the ZWO cam I have a USB3 cable from PC to the imaging camera and as the ZWO has a two port hub built in, short USB cables from the main cam to the guider, and main cam to the focuser.

[Astronut07]

Martin

Thank you for information