connecting PHD2 / Windows to Celestron CGEM

[Florin Andrei]

I'm new to auto guiding.

I am going to use an ASI camera on an off-axis guider OTA to feed images into PHD2 via USB.

I need to connect the laptop running PHD2 (on Windows) to my Celestron CGEM mount. I assume some kind of USB-to-serial converter is needed. I already have one:

https://www.amazon.com/TRENDnet-Converter-Prolific-Chipset-TU-S9/dp/B0007T27H8/

But if that converter is not the best, I can get a different one.

Now I assume I need some kind of serial cable to connect the RS-232 port on that converter to one of the many ports on the CGEM mount or the Celestron hand control device, whichever is preferred. What's the best way to achieve this?

For now, please assume I am tracking / slewing / driving the mount with the Celestron hand control, and I'm only using PHD2 to apply autoguiding corrections. Perhaps in the future I'll use a laptop-based app like Cartes du Ciel to drive the mount, but that will not happen any time soon. But if I did switch to the app, how would that change the connection scheme? Can I use the same serial cable to drive the mount, but also for the autoguider, or are those connections separate?

Do I need to install some kind of ASCOM driver?

I'm just trying to figure out what's the "canonical" way to connect PHD2 to the CGEM. I've seen some recommendations online, but there doesn't seem to be any consistency there.

Thanks!

[peter wolsley]

Florin,

If you plan to use your handcontroller to track, slew, calibrate, align etc. then you will not need any serial cable or USB to serial converter.  You will need a USB cable to connect your ASI camera to your computer.  I would assume that the ASI camera also has a ST-4 port which you will use to connect your camera to the CGEM mount's "AUTOGUIDE" port. The CGEMs HANDCONTROLLER, AUX and AUTOGUIDE ports are NOT interchangeable...resist the temptation to plug things in differently. Configure PHD2 to use your camera and for "mount" select "On Camera".  This arrangement should get you up and guiding.  The only caveat is that every time you slew to a target you will first need to perform a calibration in PHD2.  Just getting this much hardware up and running is enough for a first step.  When you decide to go further and begin connecting the mount to your laptop you can repost your question and we can go from there.  When you do you will need to purchase another cable that will connect your USB to Serial cable to the bottom of your handcontroller.  This link is to a cable on Amazon https://www.amazon.com/Celestron-Nexstar-232-Interface-Cable/dp/B0000665UZ/ref=pd_bxgy_147_img_3?_encoding=UTF8&psc=1&refRID=XV5TW6TRKSVZV0QCM77E.  It's also available from Celestron.

One step at a time...

Peter

CGEM owner

[Florin Andrei]

Peter,

Thank you so much, your message has finally dispelled the clouds for me! (pardon the pun)

The camera I intend to use on the guidescope OTA is the ZWO ASI224MC. Probably overkill for autoguiding, but I am going to use it anyway as the main camera for planetary shots (which don't require guiding), so I might as well put it to good use with the autoguider when taking deep space images. It does indeed have an ST-4 port, and an ST-4 cable is included in the box. I am going to try this soon.

The main camera I intend to use for deep space, plugged in the main OTA, is the ZWO ASI071MC-Cool. I think I am going to plug the 224 into the USB hub on the 071, and then run the USB3 cable from the 071 back to the computer. I think that should work just fine.

Separate but related question: let's say I want to image the Sun through a full aperture white light filter. I am going to use the ASI071 for that purpose, because the bigger sensor allows me to capture the whole solar disk at once. The 071 does not have an ST-4 port. In that case I believe I'll have to get the Celestron Nexstar RS 232 PC Interface Cable that you indicated, and connect the laptop to the RS-232 on the bottom of the hand controller. But in that case I'll autoguide with Firecapture - the latest beta version allows you to autoguide on sunspots. Does that sound right?

[peter wolsley]

Florin,

Solar is very simple with a white light filter.  The amount of light that pass thru the filter allows you to use very short exposures which all but eliminate blurring.  You won't be guiding...PHD2 is not designed for solar...it wants tiny stars and inky black sky. You will find that alignment/calibration in the daytime will force you to use your last alignment(if you have a permanent set-up) or a quick align.  You will need to tell your handcontroller to allow you to select the sun.  Once you have slewed to the sun you will need to manually slew at slow speed until you have the sun centered on your imaging camera.  The mount will track the sun which will minimize how much you need to manually slew to keep the sun centered.  Don't use your guiding camera...a mistake during solar photography can fry the chip if it's exposed to direct sunlight.  Take lots of photos and plan on stacking them using a program like Registax.  So you don't need to buy that extra cable just yet.  I did a series of solar photos thru a white filter using a Dob with no motors.  Images were crisp.  Your biggest issues will be focusing and getting a good shot where air turbulence is lowest.  Try this arrangement first...getting things going during a sunny day can be tricky.  Also your telescope will be heating up and that will cause thermal columns to develop in the scope...they will blur your photos so you need to be efficient.  Just remember that your scope is just like a big magnifying glass.  If it gets a bit of unfiltered light thru it...it will quickly fry anything that tries to catch the light.

Good Luck

Peter

[Florin Andrei]

Oh, I am aware of the risks. I've done solar photography before with a Dobsonian.

http://imgur.com/a/KWx5f

http://imgur.com/a/TGqlG

http://imgur.com/a/D6qmG

I have Baader filters for everything, including finderscopes and binoculars. :)

This time around it's a bit of a special case.

What I'm trying to do now is taking snapshots at regular intervals for a long time - several hours. Because I'll setup the mount during the day, it won't be in perfect polar alignment. So the image will drift. I would have to manually adjust it every once in a while.

However, Firecapture can autoguide based on sunspots. It's a new feature in the beta version. With autoguiding, I could just start the process and then let it do its thing, the Sun will remain inside the image frame, no manual adjustments necessary.

The only thing not clear to me is the various ways to connect the laptop to the CGEM mount.

[peter wolsley]

Florin,

I would first want to know how Firecapture wants to guide your CGEM.  If Firecapture can use the ST-4 port on your camera then, once again, you don't need to communicate to the CGEM.  If Firecapture wants to talk to the scope either directly or thru ASCOM then you need the interface cable I mentioned.

There are a couple of ways you can get software like Firecapture to talk to your mount.  Regardless of which method you use...you will need to use the USB to serial converter cable and the RS-323C to handcontroller cable I mentioned.  You will need to connect these cables together. Plug in the USB end into a spare USB port.  As soon as you do this Windows will assign the USB to Serial converter to a specific COM port.  Make a note of this COM port (use device manager to determine what COM port has been assigned).

This is where choices start happening.  There are some software programs that can "take it from here".  They normally describe this method as "direct to mount".  StellariumScope can do this.  I believe there are few programs that have this ability simply because each program has to understand lots of interface details about your specific mount.

The more common method is to use ASCOM.  You will need to download and install the ASCOM platform 6 and you will need to download and install the Celestron Unified ASCOM driver.  You will need to configure the Celestron Unified ASCOM driver to use the same COM port as was assigned to your USB to serial converter.  Once this is done you should be able to select the ASCOM interface method in Firecapture to communicate with your CGEM.  You will still align/calibrate/slew using your handcontroller but now, via the cable plugged into the bottom of the handcontroller you can have Firecapture guide the CGEM.  With this method you don't need the ST-4 cable...you should disconnect it when using this method.

I use a more complicate version of this method where I introduce Nexremote into the mix.  Nexremote is a Celestron app that emulates all of the functionality of your handcontroller.  You still need to keep all of the cables plugged in as before...you still need to have your handcontroller plugged in.  I operate my mount remotely.  Nexremote allows me to align/calibrate/slew using an app that looks identical to my handcontroller.  I don't have to be out with my CGEM to use my system.  I have a stepper motor moonlite focuser so I also focus remotely.  The Nexremote app has what it calls a "virtual port" which allows Nexremote to act like a pass-thru device.  I select a virtual port number (for me it's COM7) and then tell my Celestron unified ASCOM driver to use COM7.  With this set-up I can align/calibrate using Nexremote, use PHD2 to guide via ASCOM and never have to be at the mount except for initially polar aligning.

Regards

Peter

[peter wolsley]

BTW,

Great solar photos!

Peter