Ingredients: A Dobson Goto Skywatcher Telescope, a CCD camera (but a DSLR will be fine as well) and a PC with Astroart 5
First of all let me introduce myself. I am an italian astro addict. I have started as a visual observer, but from many years I do astropohotography. Always from my terrace in my hometown, Prato, a 200.000 people town in the heart of Tuscany. Just 10 km from Florence. I have done over 600 images in 10 years, as you can see from the astrophoto area of my website. In 2011 I have bought a wonderful Dobson Skywatcher goto 12 inches. That's the biggest scope I have ever had. The temptation to do some astrophotography was very strong. Dobson telescopes have one major problem to solve: the field rotation. But before of that, I have found out that the drivers needed to connect to the pc (both Celestron/Nexstar and Ascom) don't support pulse guiding. This problem broke me all the tests I have done to guide this scope, with every software. How to solve this problem ? I have tried a different approach: short exposures. Imaging with this technique is very close to "video imaging" and doesn't need guiding. First results were very much interesting:
m13 - Sum of 100 5 seconds exposures with a DMK camera
m27 - Sum of 888 5 seconds exposures with a Lodestar Camera
ngc 7635 - Sum of 65 5 seconds exposures with a modified Canon 1100D
The final idea was to find a system to keep the object in the middle of the frame during the night, without any human correction. I have tried Maxim DL, but I have had some troubles due to the software calibration. The telescope started to turn around bringing with himself all computers, cables, and so on. A mess.
I have decided to make some tests using Astroart 5 and its scripting functions. I have some programming skills, but it has passed a very long time without practicing.
I made the script copying examples on Astroart manual. Before appliying the script it's very important to follow the instructions in the manual for the solve plate function. It's necessary to fill all the correct data. My suggestion is to try to solve some images that you have in your pc, before trying to use the script in the field.
First results were very much interesting. The software kept the object in the middle of the field for about 5 minutes, and then moved in a top right part of the frame for the other 5 minutes. It was like a little ballet, but I was definitely on the right track. The examples below are done with an Atik 383 l+ in binning x 2 and an Idas LPS2 filter:
Sum of 90 5 seconds exposures
Sum of 30 5 seconds exposures
Some changemnts in the script were needed. I did these changements, and in the night of the 24/09 I have been able to keep the object in the middle of 940 10 seconds frames:
Sum of 800 10 seconds exposures
140 frames I had to cut due to the fact that some clouds covered the sky. There is some out of focus, due to the fact that the camera was not properly connected to the focuser (I really had no time to do some proper focusing that day). You can download the script from here It worked in the night of 24, but it's very important that the scope is properly balanced and that there is a very little or almost no wind
I have done another script that should work almost authomatically and can manage more than 1 object per night. I have not tested yet (some rain and bad weather arrived in my country).you can download it from here Before testing it have a look at Astroart manual and instructions. All variables are in the beginning of the script: t is exposure time, totale is the total number of frames, maxDist is the maximum distance allowed from the center of the frame
Try the script at your own risk...let me know if you have found it useful
Stefano Ciapetti - astrociap
