Re: Dob Flexion (was Returned Messages)
Chuck Grant (grant@aretha.llnl.gov)
Thu, 20 Apr 95 10:38:33 -0700
> From: espector@mltsa.mlm.att.com (Edwin Spector)
>
> I don't understand all the fuss about flexing in Dobsonian
> groundboards due to bearing position. If these are (say)
> 3mm PTFE, it would take a pretty big warp before something
> started fouling. With 3/4 inch ply, that would be a very
> heavy telescope :-O
>
> On a lesser scale, a warp of even 1mm should not cause
> problems (I think). After all, this is a Dob, not an
> equatorial. You have to nudge it all the time, anyway.
>
> Sorry if I've missed the point.
>
> Regards
>
> Edwin Spector
> edwin.spector@att.com
>
My point is not static flex. My point is dynamic flex: vibration when
touched and springiness that makes the scope bend when pushed and then
snap back into place instead of smoothly slipping on the bearings and
staying pointed where you pushed it. Of course for a small, light
weight telescope used only at low power, just about anything will do.
But if you are trying to build a large, high performance instrument
everything becomes more critical.
If you have ever pushed around a good, big dob with a stiff truss and
"that buttery smooth feel" at over 300x then you now how nice it can be
and will never want to go back.
Chuck