Alan Branch said:
THe fine focus on my ZS80II slips with or without a load.
I have adjusted the main focuser in accordance with the manual and it works fine.
Is there an adjustment for the fine focuser, or is this just an inherent problem
Alan
Hi: If one is adventurous and somewhat mechanically inclined it is possible to adjust the fine focus. However it is not so straight forward. I believe Pollux Chung has a tutorial for the GSO two speed focusers, the William Optics focusers are similar.
First though, it is my experience that the fine adjust will likely slip if the main focuser has too much preload. You probably need to play with the main focuser adjustment a bit more.
The fine focuser uses three large ball bearings as "planetary gears." These are preloaded and are driven by friction rather than actual gearing. So like an actual Crayford focuser, they are sensitive to the amount of preload. Too much they do not work properly and may also become notchy like an over tightened wheel bearing on a bike. If there is not enough preload then they will slip. It's a fine line and the added problem is sometimes the nut that adjusts that preload is secured with Locktite or something similar.
I suggest starting by readjusting the main focuser and seeing how that works. If you adjusted the main focuser because you are trying to use a heavy two inch eyepiece, you maybe stuck between a rock and a hard place.
In my experience the Asian focuser are quite nice when you considers that a Feathertouch or Moonlight two speed would cost more than half of what the scope did. On the other hand, it is also clear why it is that more than a few owners upgrade to the Premium focusers. And it is probably worth noting that the high end Feathertouch Focusers, the ones Roland uses on his scopes, are actually rack and pinion focuser rather than Crayfords...
Here's a question for the rest of you: The use of preloaded ball bearings as planetary gears is clever, I am curious if any one knows who built the first fine focus adjuster using this design. Maybe JMI or Starlight Instruments (Feathertouch)??
Jon
