The LHIRES III spectroscope is focused by taking a side panel off the instrument and turning a lens holder with a thread on it. This moves the lens in and out, and in so doing adjusts the instrument focus. Each time it is turned the panel has to be replaced so that an image can be taken to see if the focus has improved. The spectroscope is shown above with the panel removed to show the focussing mechanism.
The spectroscope is made out of thin metal, and I find that when there is a drop in temperature there is a significant change in focus. Some people report that they do not find the focus changes much, all I can say is that at times I have, perhaps some nights there is a bigger temperature change than other nights, but it is an issue for me.
I find the whole process of focussing awkeward, and I have found that this deters me from using the spectroscope. I tend to run the set up remotely, so having to go out, unplug everything, focus, then get everything working again is a bit of a pain. Also, having to take the side panel off, adjust the focus, put the side panel back, test the focus and repeat until focussed correctely is a nuiscance. I have therefore been looking for a solution for this for some time, and the result is described below.
I recently bought a Moonlight focuser with a Lakeside Astro motor and controller from Ian King Imaging, and looking at it thought that it might be possible to come up with a bracket design that would enable me to use the Lakeside motor system on the spectroscope. I put some drawings together and sent them to Ian who passed them onto Peter at Lakeside Astro. Peter suggested a much simpler design that the ones I had come up with and the result is shown below:
The final test set up is shown to the left. The focusing system is working very well in tests giving smooth and accurate movements. I am really surprised at how well it is working, I thought that I would need to do more research to find the right drive belt or change the drive motor wheel. One worry I have for the future is how the elastisity of the drive belt might change in cold winter nights and whether this might affect the effectiveness of the focuser, however, I will cross this hurdle if it becomes a problem and will post results here if it becomes an issue. For now I am very happy with this new focussing mechanism and am looking forward to using the spectroscope more than I have in the past.
The next question was what to use as a drive belt. A trip to B&Q provided me with an O ring from a Marley universal trap seal replacement kit which had the sort of properties that I was looking for, not too elastic, fairly thick and the correct size. While I was out a trip to Maplin also furnished me with a small box (part LH57M) which looked like it would provide me with a cover for the drive system to stop light from entering the spectroscope.
Below you can see the set up with drive belt in place and with the cover in place.