I have now added an autoguiding port / functionality to my camera tracker. The autoguider will allow me to take long exposure images where the camera guider will make small corrections to keep the target perfectly still on the camera sensor. This is quite a complicated setup to get right and I am sure that it will take me some time to get the results I want.
It is possible to purchase these type of telescope mounts that will do an excellent job at guiding but I enjoy the thrill of designing and making my own equipment.
For more details about my original camera guider, look at https://starsinphotos.wordpress.com/2012/03/29/camera-tracker/
The camera tracker uses an Arduino processor to do the timing for the stepper driver to make sure that it can be accurately controlled. I have now added a few features where I use a modified webcam as a guiding camera on the star tracker. Software on the laptop measures the drift of a guide star and provides correction pulses via the parallel port (ST-4 type interface) to the Arduino. The Arduino then drives the stepper motor a little bit faster or slower depending on the drift of the guide star towards the west or east. Refer to the following schematic:
I am using a Microsoft Lifecam Cinema webcam for the guide camera, The webcam has been modified to work at prime focus and is used with a bracket that allows it to be mounted onto a standard Canon EFS type lens.
This works well on the test bench and I am almost ready to test outside. I still need to make a bracket to mount the webcam/lens combination onto the camera tracker on a separate ball head so that a suitable guide star can be selected.
I will add some photos and arduino code when everything works, so come back and check again later.
Updated on 4 April:
I tried to test the tracker last weekend, it was quite dark but unfortunately the clouds and thick fog rolled in before I could get anywhere. The dew was unbelievable. Obviously I packed everything up and got back home without taking a single photo.
I will try the tracker out tonight at home. Its less effort than travelling 40km to a dark site.
Updated on 5 April:
I was out there in the cold all night last night and was 100% unsuccessful. I could not figure it out. I know it is difficult to get the tracking parameters right when you are using a DIY mount with unorthodox motors and gears but this was something else. I gave up at 3am and continued testing today by aiming the webcam at a white dot on black paper on the wall to look at the log errors from Guidedog 1.0.6. I then plotted the log file on Excel. If the mount, motor and gearbox works as it should, the resulting graph should be a straight line centred on the sidereal rate of 15.04 arcseconds of movement / second. In this case it was all over the show with wild 20 arcsecond oscillations. I took a photo tonight outside with the mount totally unaligned with the celestial pole and took a 5 minute exposure with the tracker switched on to see what it would do and the result is wavy star trials.
The bottom line is I have to trash the tracker or rebuild it to be much more solid and avoid any flex in the gearbox. It might be easier to start from scratch. At least I have the software and electronics sorted out now,
Here is a copy of the last set of Arduino code I used:
Note: Look at my later posts in this series for updated information….