Re: ATM How they used to do it

["Don Clement" <clement@san.rr.com>]

Hello Jim,

I built a similar focus mechanism for an 8" f10 mak-cass using three
lead-screws tied together with a Berg cablechain. The nut for each
lead-screw was fixed to the backplate with two duplexed BB races. The
alignment of the lead-screws was accomplished by letting each duplex BB nut
assembly float radially. Then when the whole focus mechanism was assembled,
the bearing placement was fixed. Performance of  the three lead screw moving
mirror focuser was better than current commercial sliding arbor types, but
still not as good as I was wanted. The optics for the 8" mak-cass were made
by Max Bray. Max said that the mirror was made with a Blanchard ground C10
blank lefover after the C10 had ceased production.

My ultimate solution was to invent and build a moving mirror focuser which
has none of the drawbacks of all the other types of focusers. The only
sliding  or rolling part of my focuser is a single leadscrew (commercial 1"
micrometer head) that precisely fixes the focus with no backlash. Since
there are no sliding or rolling parts other than the micrometer head, there
is no lubrication required. The problem of "old grease" is eliminated. My
focuser will work the same now as it does in 35 years or work the same in
the vacuum of space as it does in the dirty conditions of observing down
here.

I have currently built a prototype of my patented moving mirror focuser to
be installed in a Fastar C14. The focuser fits in the available space behind
the mirror inside of the rear casting. My focuser eliminates the mirror
flop, image shift, lubricating grease,  and backlash, but adds the ability
to collimate the focuser  mirror assembly  from the outside rear of the C14.
The C14 and my focuser were fully modeled using Solidworks 2000 before I
began the machining process.

Don Clement
San Diego/Running Springs



>   I got stuck with trying to fix our aging club telescope.  A 34 year
> old Celestron C-10.   >   The two main problems at the moment is very
stiff focusing and the
> clutch on the RA is slipping.  The focus is probably just 30 year old
> grease but I don't what to take the focus mechanism apart (see photo's
> below) to avoid having to realign the three separate focus knobs.   The
> clutch was repaired ten or so years ago with some sandpaper in the
> clutch so I may try that again :-)
>   The focus mechanism is very robust compared to the ones used today, as
> anybody with a meade and the half an inch of focus shift knows.   The
> bottom plate is held in to the back cell with three screws and rests on
> three set screws for collimation.
>
>
>
>