Re: ATM home made secondary holders and spiders

["Arjan te Marvelde (ELN)" <Arjan.te.Marvelde@eln.ericsson.se>]

> traditional 120 degree adusting procedure. Also the mirror is much
> closer to the supports, most designs have the mirror sitting on the end
> of a pendulum of several inches, just inviting vibrations, with this
> design the center of the mirror is very close to the center of the
> spider vanes. 

Johnny,

For a very simple, all metal, low profile spider see
http://home.hetnet.nl/~artm/atm/design.html
at the bottom of the page. 

It's only a drawing, but i've actually made the thing in an hour or so. Images will follow in due time.

The straight part is suspended with two steel metal bands (as those used for bundling street tiles). The bent part is attached to the straight part with three screws and a steel ball serving as bearing. 
After you cut and bent the aluminium parts, drill the holes for the adjustment screws, cut some thread in the bent part and widen the hole in the straight part. Then drill a small hole in the middle that can serve as a guide for the large drill bit used to make the ball seats. Finally, you cut slits where the steel bands go.

The moving part can only roll over this steel ball, provided the screws are fastened, thus giving 3D motion. The upper screws give paraxial rotation, and the bottom screw adds a perpendicular component.
The spider has a fixed position along the scope axis, but in my case this is accounted for by some slop in the focuser mounting. 


Hope this may help,
 ... Arjan te Marvelde