13.02.2020 180mm refactor, FT focuser adapter and backplate.

 *

Thursday 13th: Spent some time "playing" with the focuser backplate of the 7" refractor. I had a threaded ring, focuser adapter made by Teleskop-Service. It works fine with the FT focuser. Though getting the clamping and friction levels correct has taken a lot of time. It relied on the thickness of the backplate for proper clamping.

I finally got rid of the springs. Which I have always used for focuser collimation on the 7". Springs simply didn't work no matter how stiff they were. They always ended up squashed flat or floppy. I just didn't have enough thickness in the backplate for threaded holes for collimation, "push" screws.

Now I have replaced the springs using nuts as spacers. These are placed on the long screws which hold the back plate onto the main tube. I added a combination of roofing washers and rubber tap washers. The latter are used as sliding friction devices for adapter ring containment. Otherwise the spacers and retaining washers can fall off, out of sight inside the backplate, without my knowing.

The focuser now turns correctly and is finally rock solid. No more shake. I should have bought an official FT adapter when I bought the focuser. But I just could not bring myself to spend so much. Besides, none of the available FT adapters really suited my needs. Another and convincing reason not to waste hundreds of £ounds equivalent. A simple flange adapter would have been good but require a whole new backplate. Instead of the saucepan base I have used since building the refractor. In reality I should have found another saucepan. One with a much sharper curve between the base and sides.

*