Can you get a focuser that remembers?

[evilgeenius]

OK I might just be living in la la land here, but can you buy a focuser that can somehow remember the positions at which focus was achieved with different eyepieces?

I have a CPC925.

[pete_l]

You can get focusers with engraved scales, so you can read off a particular setting and return to it at a later time. But there are some other factors to take into account, such as focus changing as your 'scope expands/contracts as the temperature changes. Also, focusing is not a precise art (and neither is focusing mechanisms inside telescopes), so even setting your focuser back to the exact same point won't guarantee you'll get perfect focus again. Even if you approach focus from the same direction (e.g. turning the focus know clockwise or anti-clockwise) each time. You can also get electronic focusers with motors and digital readouts.

There is an alternative: parfocal rings for your eyepieces. Briefly, these are metal rings that slide onto the sleeve of each e/p. You put one on each eyepiece you have and then adjust perfect focus with one of them (having tightened up the parfocalising ring, so it won't move). Them, without touching the telescope's focuser, try each other eyepiece in turn. Put that in the 'scope and move the eyepiece itself up and down until you get focus, then make sure that e/p's ring is against the rim of the telescope's focusing tube and tighten the ring's grub screw so it won't move.

Now you have a set of eyepieces that will all be in focus when you change them, without having to alter the focus settin of your telescope.

[John]

.......or you can get a set of par focal eyepieces which all reach focus at more or less the same spot