DIY Autoguider for Long Exposure Astrophotography (Part 4)

I tried the upgraded autoguiding tracker again on Wednesday and the results improved quite a bit. I used a 250mm lens to image the LMC. The following is a photo of the PDH graph showing the tracking error. The error is a small fraction of pixel. It has improved a lot since the previous test where the typical tracking error was ±3 pixels.


The resulting images of the LMC are not great due to the light polution but the tracking is starting to show promise.This is a single image (no darks or flats) taken at 60mm, f/2.8, 120 seconds and ISO 800 showing some round stars. Some cropping, levels and stretching was done with Lightroom 4.

IMG_6253 bright-1

This is the setup I used:



I used a Canon 18-55mm lens for the guide webcam. Tracking accuracy will improve a lot if I increase the focal length for the guiding, maybe use a 18-135mm. The zoom works well on the guide camera to find a suitable guide star.

The advantage of this mount is that it can take a bit of weight. I tried to mount an Orion EON 80mm on and it did not complain too much. Maybe I will need to modify a bracket to make sure the camera mount ball head cant slip with the 80mm scope. I will try that next.

Here is the latest version of the Arduino sketch:  Stepper Motor sketch (pdf download)



4 thoughts on “DIY Autoguider for Long Exposure Astrophotography (Part 4)

  1. Pingback: VicSouth Desert Spring Star Party | stars*in*photos

  2. Harald Duennfelder

    Hi Theo,
    wow, that’s an impressive job you habe done. Congatulations. It’s always satisfying seeing it working as it is planned. I’m working in building an Arduino controlled barndoor mount, but I’m looking for alternatives as well and your autoguiding system might be one. But there are some questions I would like to ask: How are the connections done?
    The webcam to laptop probably via USB-port and the PHD-Software will find it. OK. But how is the connection from the laptop to Arduino? I saw your graphic on part one, but I don’t know how to realize it. So I hope for some help of yours.

    Thank you very much ahead
    Harald from the other side of the globe 😉

    1. Theo Post author

      Hi Harald,
      Thank you for your comments. I always knew that I should document the circuit diagram as others may be able to use this. All the individual parts are quite simple, the issues start when you try to make it work. I learnt a lot of lessons there!
      I will draw it all out and put it in a new post on the blog. I will send you a message when its ready.

  3. Harald Duennfelder

    Hi Theo,
    thank you for your quick response to my questons. Your answers and the diagram helped a lot. It isn’t as difficult to rebuilt as I thought to be. And the Arduino sketch looks pretty simple too. Maybe it’s even possible to adapt it to the contolling sketch of my Arduino-barndoor.
    It’s probably the most difficult part to get the connection PC to ST-4 done because it’s hard to find a laptop with a parallel port, but I found an USB to ST-4 adapter online.
    So thank you very much again for your help and I’ll give you a notice when my construction is working.
    For the moment I wish you a nice christmas


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