Instructables

1.25" Crayford Focuser with Eccentric Tensioner

Picture of 1.25

 


Almost a year ago I decided to make a Dobsonian style reflector telescope. I finished it late in the spring and was able to enjoy it all summer, fall and even a little during the winter. I've observed Saturn, Jupitor, star clusters, nebula and spiral galaxies. It truly was a rewarding project and I still use it on a regular basis.

When I built my telescope I used a 1.25" rack and pinion style focuser. It has worked OK, but I knew there had to be something better out there. The motion on the rack and pinion focuser is not very smooth and it seemed to make large jumps in focus for small movements at the knob.

After some research I discovered that many amateur telescope makers use a Crayford style focuser due to its simple design and smooth motion. Many focusers also make use of a planetary reduction knob for fine focus adjustments. With these design goals in mind I set out to make my own.

Please be sure to read my summary at the end if you want to follow my Instructable to make your own focuser. I give a review on how well it performs and what changes I plan to make on my next revision.


 
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Tex Arcana7 months ago
To put it simply: metal. It's the only way you're going to get the rigidity you need out of this. Since weight isn't an issue, steel is your best bet. It'll be easier to weld and machine, and way more exact and stiff.
melvinkat (author)  Tex Arcana7 months ago

I agree. I was also thinking that the next one I make will be out of metal. However, I was leaning toward aluminum. Weight is a concern because I need the telescope tube to balance at its side bearings. This focuser, made out of acrylic, is heavier than my old one and I had to move the tube back in the cradle to adjust the balance. There is not much more room left to move it before it hits the base. I could, however, use some counterweights if I needed to.