AstronomyShed Tutorials 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.

Figure(1) 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.

Figure(2)

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.

Figure(3)

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.

Figure(4)

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.

Figure(5)

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.

Figure(6) 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.

Figure(7)

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.

Figure(8)

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.

Figure(9) 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.

Figure(10)

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. To follow, Autoguiding - Part - 2 Software setup. Autoguiding - Part - 3 Use.