I think a better idea is to put a focal reducer or teleconverter in the back
of the scope which is able to be moved back and forward, with the camera
held in a fixed position, to achieve focus. This solution has the advantage
to deal with a total focal ratio of (just as example) f10 in comparison to
your solution around f2 (primary mirror only). The smaller the f ratio the
higher the focusing accuracy.
The other reason not to use the secondary to focus is you really don't want
to put to much weight on the corrector plate.
Renato
> -----Original Message-----
> Heapy Chris CG
> Sent: Thursday, 28 January 1999 21:18
> Subject: [M]: LX Focussing Strategy
>
>
> A hypothetical question:
>
> If one were to replace the secondary holder with a modified
> version capable
> of being moved (powered by a radio-controlled motor), would the change in
> geometry adversely affect the image?
>
> The potential advantages are:
>
> The main mirror could be positively locked in place without worrying about
> attaining critical focus first.
>
> The lightweight secondary could be moved precisely without danger of it
> flopping around, a leadscrew and 3 linear bearings would assure this.
>
> Plenty of room for motor/leadscrew/reduction gearing - though the
> secondary
> housing would need to extend forwards.
>
> The radio-controlled servo motor would not introduce diffraction artifacts
> the way a wired motor would (though the Celestron Fastar seemed
> to cope OK),
> the % obstruction would be the same.
>
> No modifications to the standard focussing mechanism (which would still be
> available).
>
> Any thoughts?
>
> Chris Heapy
>

View index by [date] [author] [subject]
Previous message: [M]: ., Gene J Ducote
Next message: Re: [M]: Piers - set in concrete or bolted on top?, Eric Schandall
Next message in thread: Re: [M]: RE: LX Focussing Strategy, Chris Heapy
Previous message in thread: [M]: LX Focussing Strategy, Heapy Chris CG