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Auto Guiding Guide


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This guide is courtesy of glider.

Autoguiding - Part 1 - Hardware setup

As a member of several Internet Astronomy Forums I see many questions about autoguiding for long exposure astrophotography being posted.

Here are 2 alternative equipment setups which I have found to be successful during my own imaging sessions.

My first setup, figure(1) consists of an imaging scope and guiding scope mounted on my Skywatcher HEQ5 Synscan Pro mount using an Astro Engineering dual bar.

The guide scope is a Skywatcher Star Travel 80 with webcam attached. In this setup I've also attached my WO ZS66 Petzval and Canon 1000D DSLR for imaging.

The role of the scopes could be reversed and the exact scope used for guiding is a matter of choice, but the ST80 is commonly used. The ST80 is actually a very reasonable achromatic 80mm scope in its own right which I find makes a good grab and go.



In order to reach focus with the webcam which I use for guiding I have to include an extension piece in the guise of a 2x Barlow with the lens removed from the end, figure(2).

It is also possible to simply use the diagonal which came with the ST80. However, I think the Barlow approach removes an opportunity for flexing to occur in the optical train which would cause problems. I've not seen flexing, but can't see the point of risking it.



The imaging and guiding cameras are connected via USB to my Netbook. You can see in the photo, figure(3) that my guide camera is a long exposure modified and repackaged Philips SPC900NC webcam.

When guiding I have never had need to use the LX mode in order to capture a star for guiding. This could be a coincidence of the Deep Space Objects (DSO) that I have imaged so far all having a bright star in the same field of view (FOV).

I could use the LX modification or my Meade DSI IIc for guiding if needs be.



The mount is connected to the Netbook via a USB to RS232 serial converter, figure(4). This connects to the RJ11 socket on the base of the mounts handset. This is the same lead that can be used to upgrade the software on the Skywatcher handset.



The handset is also connected to the mount using an RJ45 lead in the normal way, figure(5). If so desired the handset could be removed and the Netbook connected to the mount using an EQDIR connection. This would go from a USB port on the Netbook to the mount RJ45 socket directly.

Note that there is no connection to the ST4 Auto Guider port on the mount, far right of figure(5). When using a camera for guiding that has an integral ST4 output the camera is connected to this port, aswell as to the guiding PC.



The Netbook has 3 USB ports which are all used, figure(6). I use a Netbook for convenience. The Netbook is smaller and lighter than a laptop, yet has enough disc space and processing power to run the software necessary for guiding and operating the guide camera, mount and imaging camera. Software is covered in Part 2 of this tutorial.



Obviously this amounts to quite a few cables trailing around the mount tripod. This can be a problem in the dark. In order to tidy things up I have devised the following cable tidy, figure(7).

Built into the box are;

  • A 7 port powered hub.
  • A 12Vdc to 5Vdc @ 3A power supply for the hub.
  • 4 USB ports are brought out.
  • 2 ports are converted to RS232 serial and brought out.
  • 1 port is converted to serial 5V TTL levels and brought out as an EQDIR connection.


When using the cable tidy I only have to run 1 USB cable back to the Netbook which can sit in the house. I use a 5m powered USB 2.0 extension and have had no problems running the mount, imaging and guiding cameras down it, figure(8).

The cable tidy also gives me a spare USB to RS232 connection for controlling the LX mode on the guide camera if it was ever necessary. It is a feature of the Meade DSI IIc camera, and some others that it requires a USB 2.0 connection.



An alternative approach to guiding is to use a modified 9x50 finder scope as a so called Finderguider, figure(9). I find this approach especially useful when imaging with my Skywatcher Explorer 200P. The additional weight of an ST80 guide scope rapidly approaches the 17kg carry limit of the HEQ5 mount.

Since the 200P optical tube assembly (OTA) includes a 9x50 finder guiding can be achieved with no additional weight added accept that of the guide camera. I also use the Finderguider on my ED80 OTA without resorting to the AE dual bar.



I have mounted the Finderguider in a set of tube rings to allow some movement when finding a guide star, figure(10). However, this adjustment has never been necessary.



Both of these approaches are also applicable to my Celestron CG5-GT Advanced Goto mount given that I use a correctly wired RJ11 plug into the back of the Celestron handset. The wiring is not the same as that for the Skywatcher handset so a separate cable is required.

Parts 2 & 3 to follow.

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Autoguiding - Part 2 - Software setup

This is the second of 3 parts detailing my experience of auto guiding for astrophotography.


My software of choice is PHD by Craig Stark. Other software exists but this is my favourite.

The first thing to do is to download and install the latest release from the

Stark Labs website, as of 13/3/11 this is at V1.12.3.

You should then download and install the latest version of the ASCOM

platform, V5.0b and the ASCOM platform 5.5.1 update.

Lastly, download and install the latest ASCOM Celestron Telescope driver, V5.0.23. I use this driver rather than the latest EQMOD driver whether I am using my Skywatcher HEQ5 Synscan Pro mount or my Celestron CG5-GT Advanced Goto mount. This is just my personal choice.

You will also need the appropriate drivers for you guiding and imaging cameras installed.

All of this software is freely available on the internet. To date I have successfully run all of this software under Windows XP (SP2), Vista and Windows 7 (Starter SP1).

You should setup your hardware as per the first article in this 3 part sequence.

Configuring PHD

Now run PHD and follow this sequence to configure the program to use your guide camera and your mount.

Firstly, to select your guiding camera click on the camera icon at the bottom left of the PHD program window.


The resulting pull down menu shows the available types of camera that work with PHD. For my basic guiding I select WDM type webcam. I could select Meade DSI as I have one of these too.

If you intend to use LX mode with a modified webcam select one of the Long Exposure webcam options depending on how the mode is controlled on your webcam. Your webcam and Webcam LX control is configured later.


Because I've selected WDM and since my Netbook has a built in camera I'm further prompted as to which webcam to use.


I then select 640x480 resolution and I420 Codec. Various options are available but I have never had need to experimented with them.


Along the bottom of the PHD program window is a box from which to select your camera exposure duration. I select 2s or longer from this list. This helps avoid situations where fluctuations in seeing cause the guiding to chase the seeing rather than guide smoothly.


Guiding parameters are adjusted by clicking the Brain icon. The settings shown are those used with my 200mm Finderguider and webcam guiding setup.

This menu is also used to setup LX mode on modified webcams.


Clicking on the Cam Dialog icon gives access to the camera parameters. I select full auto.

Under the General setting tab I select all options Off.


Now click on the Mount icon to setup the mount parameters.

I select the Celestron driver. I can do this with both my Skywatcher and Celestron mounts when connecting through the handset as detailed in Part 1 of this guide.

Skywatcher handsets are Celestron Nexstar compatible. By connecting in this way I do not have to put the mounts handset into PC Direct mode. This means that I can select targets and slew to them using the handset which I keep positioned at the mount. I find this convenient if I need to do any fine adjustments or mount PAE during the might. Also when changing targets I like to be outside at the mount so I can check for cable wraps and other problems that might be occurring.

It is also possible to make minor adjustments via the small keypad window that opens up after selecting the mount driver.


Enter your scope and site values as requested. Your Serial port can be found in Device Manager.


By following this guide and the previous hardware guide you are now ready to start guiding. I’ll cover how this is done in the last of these tutorials.

For now, the following image shows my desktop during a typical imaging run.

You can see the main PHD screen with the star that I am guiding on in the cross hairs. The orange hashed box indicates low signal to noise on the guiding star, usually this is solid green. Why this can happen and what to do about it is covered in part 3.

Also visible is the PHD guiding graph, the large excursions are deliberate, they are commanded by my imaging camera software Astrophotography Tool, a feature called Dithering which helps remove image artefacts during image processing. These issues are also covered in part 3.

In the bottom right of the desktop is the mount driver keypad.


Suffice to say that if you get to this point it’s time to go and watch the TV or have a coffee whilst the subs automatically roll in!

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Autoguiding - Part 3 - Using your autoguiding setup

This is the third of 3 parts detailing my experience of auto guiding for astrophotography.


In writing this article I have assumed that you have read and followed the previous 2 articles in this series. These articles covered hardware and software setup issues.

This last part will detail how I use my autoguiding setup on a night by night basis.

Polar alignment

Polar alignment is essential for good autoguiding. Poor polar alignment will cause the autoguiding to struggle.


Many people take great pains to 'perfectly' balance their scope on their mount without realising this will actually cause problems for their autoguiding, and infact their tracking in general.

It is better to slightly unbalance the mount in both right ascension (RA) and declination (DEC) so that there is always a load on the teeth of the gears in the mounts drive train. The gear teeth are therefore always meshed together. This

helps to keep backlash at bay.

Some people say that the mount should be biased counter weight and camera end heavy, I've not actually noticed a difference which way the weight is biased, but biased it should be.

I usually balance and then move the counter weight an extra 10mm down the counter weight bar. I also balance without the camera on the telescope and then let the cameras weight supply the bias after it is attached.


The mount will usually end up with a number of cables wrapped around its legs. Even when arranged neatly these cables can snag and generally drag on the ground. The amount that they can interfere with the smooth motion of the mount

is surprising and can cause large jumps in you guiding.

Starting out

I polar align with out the telescope or weights on the mount. This makes alignment easier.

Next I fit the telescope and weights to the mount and balance the setup.

Now I turn on my PC and the mount. On the mount I enter time, date, location, etc as prompted and then make a 2 star alignment.

Next I slew to a bright star like Capella.

Now I run PHD.


Next I select my camera and my mount using the camera and telescope icon bottom left. If the HC Buttons window has come up with the main program window over them I move them to one side on the desk top.


Next I start the camera looping using the Loop icon. Using a Bahtinov mask I focus the guide camera on the guide scope using my bright star. Bahtinov masks are an essential for good focusing, even when using my 9x50 finderguider I have made a small mask.


Now I slew the mount to my intended target for the night using the mount Hand Controller.

At this point I usually go back in the house.

Now I run my imaging camera software. Depending on which camera I am using for imaging I may need to adjust my alignment slightly to get good framing. I do this framing adjustment using PHD's on screen HC Buttons menu.

Once the image is framed and the mount is tracking I look for a guide star.

Using the mouse I click on a bright star near to the centre of the guiding image.

You can also get PHD to auto select a star for you using the Tools pull down menu. Be sure not to select a hot pixel by mistake!


Also, don't select a large bloated star. These tend to have saturated the camera and result in a profile with a flat top. In this case PHD cannot accurately find the middle of the star profile.

It is possible to view the star profile using the Tools pull down menu.

Once selected a green box appears around the guide star.


Now press the Brain icon, PHD will start to calibrate itself, moving the mount East, then West, then North and then finally South. At each stage PHD is learning how far it has to move the mount to get a resulting movement of the

guide star in the image. When guiding PHD uses this knowledge in reverse to move the mount the correct amount to compensate for movement of the guide star. This movement is caused by the imperfections in the gears and motors in the mount.


The cross hairs indicate that calibration is taking place and help to show how it is progressing. In my case the green square represents +/-25 pixels in the North/South and East/West directions.


The figures at the bottom of the window show that the mount has taken 11 steps to move the mount 24.8 pixels in the x axis. I adjust the Maximum Step size parameter in the Brain menu so that calibration in the West and East directions takes about 10 to 20 steps. If it takes more then 60 steps then calibration fails. More often than not this is caused by mistaking a hot pixel for a star!

Note that during these calibration steps the image has only moved 0.3 pixels in

the y axis. This is because I always try to align my guide camera at right angles in the guide scope, either to the RA or the DEC axis.


When East and West calibration is complete the software automatically clears any backlash, then it starts North/South calibration.


North and South calibration usually take about 10 steps on my mounts, less than for East/West calibration.


Following a successful calibration PHD automatically starts guiding. I usually leave the system for a minute or 2 to settle.


I usually use the Tools pull down menu to Show Graph, which gives a graphical representation of how your guiding is progressing.


Basically you are wanting a blue RA and a Red DEC trace that show a low level, smooth oscillation about the mid line of the graph.

Many people go to great pains to get the graph as flat and as smooth as is possible. I follow a more practical approach of only adjusting anything if the stars in my images start to look elongated. The excursions in the graph can be alarmingly high before this practical limit is reached.


In the graph below you can see excursions caused by gusts of wind, these had no visible effect on the shape of the stars in my guided images.


This is a graph taken whilst imaging M82, you can just see its outline in the guide camera image. This is an almost classic graph, low excursions, with an underlying low frequency sine wave oscillation.


In this graph, taken whilst imaging M51 you can see the effect of snagging where my camera cables were dragging along the ground as the mount moved.


On nights of variable or poor seeing it can be helpful to increase the Min Motion and camera integration time. This helps stop the system chasing the seeing rather than real errors in guiding.

High cloud can cause the intensity of the guide star to vary greatly. PHD calculates a parameter called star mass and warns if this is varying. If guiding is lost the software gives an audible warning. Guiding can be lost for several

seconds with little guide star motion detected when it returns.

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  • 1 month later...
  • 9 months later...
  • 2 months later...
  • 1 month later...

May thanks for posting this...


I found it so interesting and informative as I may well move in this direction one day and need to consider such things when planning my kit.


If you were to look through the Skywatcher Star Travel 80 in fig 1 how would the Deep Sky Objects appear?

My guess would be that the fainter ones even with low light pollution and good seeing would not be detectable?


As my first serious set-up I was wondering if I could get away with a 80mm refractor on a quality mount such as the NEQ5 or should I be looking to get a 200P or 6 RC or what?


Funds are not endless as I'm retired so I need to choose carefully and so your input would be appreciated.





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It's unlikely you would 'see' the DSO through the ST80 but then it's only there to lock onto a bright star for guiding.


I usually image with the ED80 and finder guider on an HEQ5 Synscan Pro, as in figure 9. Perfectly adequate for me.


Otherwise its WO66/ED80 and the ST80 for quiding.

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It's unlikely you would 'see' the DSO through the ST80 but then it's only there to lock onto a bright star for guiding.


I usually image with the ED80 and finder guider on an HEQ5 Synscan Pro, as in figure 9. Perfectly adequate for me.


Otherwise its WO66/ED80 and the ST80 for quiding.

Thanks for your input - All understood.

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many many thanks for posting this tutorial Noel, i changed my setup the other night and tried imaging with the Atik Titan guiding with the webcam but couldn`t get a image of anything on the webcam chip for it to follow, all i was getting was a jet black background with thousands of white specks dancing around on the screen,

i remembered you had posted this tutorial and changed the advanced settings in PHD and was guiding within 2 minutes, i haven`t a clue what any of the settings mean, unfortunately by then the fog had closed in, just my luck. 

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Rob has found me instructions on how to set my cg5 up to auto guide with the dual axis controls. I need to get a few things. St4 cables. Are these the same as telephone cables? Also st4 to usb adapter to connect to my laptop. Sorry but im not too clued up on what i need as still new to it all. Can anyone point me in the right direction? Thanks. Phil.

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Would these instructions in principal also apply to the use of an NEQ6 mount or just an HEQ5?

I would be using a finder guider, the guide cam has a usb plug that would go to the laptop. Then a usb to rs232 serial converter from the laptop to the handset? Does that sound about right?

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Would these instructions in principal also apply to the use of an NEQ6 mount or just an HEQ5?

I would be using a finder guider, the guide cam has a usb plug that would go to the laptop. Then a usb to rs232 serial converter from the laptop to the handset? Does that sound about right?


EDIT : Scrub that, I didn't see the EQDir section in the top post :)


Simple answer - yes, it's just the same

Edited by Kheldar
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:thumbsup: I was kind of hoping that you would read this Stephen. Thanks for that. I know you did your best to explain everything to me but I have slept since then :D and it is a lot to take in.

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Much simpler i find just to go with the eqdir cable and do away with the hand controller, but the system works just as well if you want to keep the handset, I can't remember the last time I used it

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