Should I use the ST-4 port?

[Larry 1969]

Hello all!
I'm brand new to guiding and just bought my first guiding set-up. The camera has a mini USB port and cable that connects to my laptop. This port also powers the camera (no additional power cable).
Also included is a ridiculously long (15 ft) ST-4 cable. I'm pretty sure this is supposed to run from my camera to the "guide" port on my EQ6-R Pro which I think 2 or 3 feet of cable would suffice...
Anyway, after installing PHD2 and running the set up under "mount selection" there are a few options. After reading the user guide I'm thinking that the Skywatcher ASCOM selection would be best.
If I'm reading the guide correctly, PHD2 will send the guiding signals through the USB port that I already have connected and I won't need the ST-4 cable at all. Is that correct?

I have my mount connected to my PC anyway and I'm using APT to control everything. Will PHD2 be able to send the guiding signals through the USB as well or will PHD2 issue those commands through APT?

Sorry, but I'm just not quite sure how it all works just yet...

Thanks!

Larry

[KathyNS]

If you have an ASCOM connection to the mount already, then definitely use ASCOM rather than ST-4. ST-4 will work if you have no other alternatives, but ASCOM is much more convenient and accurate. Plus, by not using the ST-4 cable, you eliminate two potential points of failure (the connectors).

The biggest advantage of using ASCOM instead of ST-4 is that PHD2 will not need to recalibrate. You do one calibration when you install everything, and it is good for the entire sky, until you change the guide camera installation. With ST-4, you have to recalibrate every time you slew to a new target.

[Larry 1969]

Thanks!
That's how I was reading it but I just wanted to be sure.

Larry

[SkyHiker]

The main advantage of ST4 is that you don't need ASCOM, which implies having a Windows laptop around. With ST4 you can get by with a Pi for instance only needing a laptop for calibration. To me that is worth the difference.

[sdbodin]

With ST-4, you have to recalibrate every time you slew to a new target.

Hum, strange, I use the ST-4 port and only cal once a night, usually near my nightly alignment star. Never a problem autoguiding.

Steve

[Graeme1858]

Here's a video on PHD guiding with a special mention of ST4 cables at 3min 27sec.



Regards

Graeme

[KathyNS]

With ST-4, you have to recalibrate every time you slew to a new target.

Hum, strange, I use the ST-4 port and only cal once a night, usually near my nightly alignment star. Never a problem autoguiding.

Steve

If your range of target declinations is not too large, it will likely work tolerably well. However, if you calibrate at M42 and then slew to M82, you will probably find that it is not sufficiently sensitive in RA.

A movement of one pixel at 5 degrees (the dec of M42) is only a few arcseconds (or fraction thereof) of RA and requires only a small correction. The same movement at 69 degrees (the dec of M82), because of the converging lines of RA, is many more arcseconds, and therefore requires a much larger correction. But without recalibration, PHD2 does not know that a larger correction is required. So the RA corrections will be sluggish.

The opposite would be true if you calibrated at high declination and then slewed to a low declination: it would overcontrol wildly.

PHD2 can only adjust for this effect if it knows the declination of the mount's targets. With ST-4, there is no direct connection to the mount, so it has no knowledge of its target coordinates. With an ASCOM connection to the mount, PHD2 is aware of target declinations, and can easily make the calculations necessary to adjust for the converging RA lines.

[dritter]

I agree with the general premise that using ASCOM is best. Simply by eliminating a cable, it is a physical improvement at the very least. And as Kathy mentions, when using ASCOM, PHD can automatically adjust for declination since it will know where the mount is pointing.

However, on one mount that I was using a few years ago, I consistently got better results from the ST4 cable. I don't know why, but that was the case. I have since replaced that mount and the new one uses the ASCOM driver and it works very well.

So I would suggest trying the ASCOM driver first and if it works well, continue to use it. But if you run into issues like ongoing inconsistent results or it does things like mysteriously dropping offline on a regular basis, don't hesitate to try the ST4 cable. At minimum, it provides a second path to the guider that you can use to help troubleshoot problems with.

[sdbodin]

With ST-4, you have to recalibrate every time you slew to a new target.

Hum, strange, I use the ST-4 port and only cal once a night, usually near my nightly alignment star. Never a problem autoguiding.

Steve

If your range of target declinations is not too large, it will likely work tolerably well. However, if you calibrate at M42 and then slew to M82, you will probably find that it is not sufficiently sensitive in RA.

Yup, makes sense, that is my usual imaging session, a narrow range of decs from alignment to targets, maybe not more than 30 degrees. Correction errors are probably lost in mirror flop anyway.



Thanks Kathy,
Steve

[Larry 1969]

Here's a video on PHD guiding with a special mention of ST4 cables at 3min 27sec.



Regards

Graeme

I'm dying!

Larry

[yobbo89]

Here's a video on PHD guiding with a special mention of ST4 cables at 3min 27sec.



Regards

Graeme

I'm dying!

Larry

haha, that's how i feel now when ever i get a planetary camera or guide camera. cya later st4 cord !, i ran my guider for over a year with the st4 cord and the usb cord both plugged in with ascom not knowing what that i didn't need the st4 cord

[JayTee]

In case you were curious, here are the phd2 reasons to use ASCOM pulse guiding.

Here are some of the primary benefits:
1) A drastic reduction in the number of re-calibrations you'll need to perform. Changing targets will not require another calibration because PHD2 can know where the scope is pointing and automatically make adjustments to the guider calibration. Most users get a good calibration and then re-use it until they make hardware changes of some kind.
2) Automatic adjustment for meridian flips - no need to remember to manually flip the calibration data.
3) Automatic adjustment of RA calibration to handle targets in different parts of the sky (declination compensation)
4) Elimination of the ST-4 guide cable as a point of failure - this is a surprisingly common problem because the cables can be damaged or confused with similar-looking cables (e.g. telephone cables)
5) Elimination of a moving cable that can snag, drag, or bind as the scope is moved around.
6) Improved ability for PHD2 to sanity-check calibration results and warn of possible problems before you waste hours of imaging time.
7) Better diagnostic and trouble-shooting information, which is particularly helpful if you need to ask for assistance
8) Availability of scope-slewing options during drift alignment which can further speed the process of polar alignment

Cheers,
JT