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PROPER PHD/ST4 AUTOGUIDING WITH iOptron CEM40

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#1 OrionNebula32

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Posted 23 May 2020 - 12:59 PM

I was just wondering who has the CEM40, or other mount that is comparable, where you have to autoguide with ST4, and how to do so. Ive only ever used RS232 to autoguide with my CEM60 and just wanna know before i take it out how to guide. From what ive read is the camera connects direct to the mount? Is that true? Where is the communication between PHD and the mount and the camera come into play here??

Im more of a hands on learner so if someone could please explain in dummy terms how to accomplish this. Will be using my Meade quad astrograph for the first time next week and want to get this down first. 

Thank you

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#2 Michael Covington

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Posted 23 May 2020 - 01:14 PM

The reason to autoguide with the ST4 connection is if for some reason you can't use the RS-232 connection.  Standalone autoguiders, for instance, use ST4.  Older mounts don't have RS-232 connections.   A newer mount might for some reason lack an ASCOM driver for the RS-232 connection.

 

There is often a USB-to-ST4 converter built into a camera to facilitate doing this.  I have never used mine!



#3 rgsalinger

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Posted 23 May 2020 - 01:33 PM

Well fundamentally you take the ST4 cable that came with the guide camera, plug it into the guide camera ST4 port, and then plug the other end directly into the mount's ST4 port. That way you don't need to connect the mount to your computer to guide. The guiding software just sends the command back to the camera which then actuates the mount's relays. If you had a true stand alone guider and a DSLR then you could lose the computer in the field and just use an intervalometer to take the shots. That's the only use case I can think of for that cable any more.

Rgrds-Ross



#4 Stelios

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Posted 23 May 2020 - 01:34 PM

Almost all guide cameras come with two ports: A USB port and an ST-4 port (looks like a phone jack but *isn't*).

 

For ST-4 guiding:

 

1) Connect the USB port on the guide camera to the laptop.

2) Connect the ST-4 port on the guide camera with a supplied ST-4 cable to the *GUIDE* port on the MOUNT.

3) In PhD2, select the guide camera as camera.

4) In PhD2, select "on camera" as the mount.

 

Guiding happens by having PhD2 send the corrections to the camera which then relays them to the mount via the USB port. 

 

You need to recalibrate on every target with ST-4 guiding.


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#5 scadvice

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Posted 23 May 2020 - 02:33 PM

A You Tube video to watch. 

 

https://www.youtube....h?v=Mt0luBLaHDw



#6 OrionNebula32

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Posted 23 May 2020 - 05:39 PM

A You Tube video to watch. 

 

https://www.youtube....h?v=Mt0luBLaHDw

Thank you, but not what im looking for here. Ive watched this a few times in the past. 



#7 OrionNebula32

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Posted 30 May 2020 - 06:34 PM

Almost all guide cameras come with two ports: A USB port and an ST-4 port (looks like a phone jack but *isn't*).

 

For ST-4 guiding:

 

1) Connect the USB port on the guide camera to the laptop.

2) Connect the ST-4 port on the guide camera with a supplied ST-4 cable to the *GUIDE* port on the MOUNT.

3) In PhD2, select the guide camera as camera.

4) In PhD2, select "on camera" as the mount.

 

Guiding happens by having PhD2 send the corrections to the camera which then relays them to the mount via the USB port. 

 

You need to recalibrate on every target with ST-4 guiding.

Elaborate...what am i recalibrating? 



#8 rgsalinger

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Posted Yesterday, 04:50 PM

Why do you think that you have to use an ST4 cable? All that you need to do is to connect the guide camera to the computer and the mount to the computer. Then use ASCOM guiding. What am I missing in all this?

 

When you calibrate using an ST4 cable, the system cannot record the declination at which you are doing the calibration. Since the move in pixels/second is proportional to the cosine of the declination, the system will not guide properly very far north/south of the declination where the calibration was done. Even worse, in that mode the system cannot know if the mount is east or west of the meridian. So, it cannot know whether or not the RA direction needs to be reversed from the original calibration. For those two reasons, you have to recalibrate for every target.

 

Rgrds-Ross




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