By request, attached are some close up shots and the design plans for my offset wire spider. The telescope is a 16" f4.5 with an 88mm secondary and I rebuilt my spider as part of an UTA rebuild to lose weight. I'm not sure that anything I've done here is terribly original, but I'm pleased with the overall result - the spider is rigid and doesn't suffer from vibration - and I thank the many contributors on this and other sites that have provided many of the ideas I have implemented together successfully here.
Key features include:-
1. low profile UTA, total height 162mm. I occasionally pack my telescope into the boot of an ordinary sedan. The photo below is my original (heavier) UTA but the rebuild (above) is dimensionally identical.
2. Guitar strings and lockable guitar machine heads make installation and adjustment quick and easy, and permit collimation. Below are two views...
The spider uses 8 x #2 guitar string wires tensioned with lockable guitar machine heads. This technique made construction very simple; I found it easier to build a wire spider than a normal vane spider. I didn't even use a jig; I simply placed the central support upside down on the table and the UTA around it (upside down) and threaded each wire from the center out through each head loosely, locked the heads, cut the wires and began to tension. When it was roughly right, fit the laser and fine tune. So there is no reason to be intimidated by wire spiders being too fiddly or difficult.
3. wire vane fixture points offset from center to edge providing stable geometry preventing rotation (yaw). See discussion of this important feature in these threads here and here...
4. spider fixing plate offset behind mirror to minimise overall height of structure and by extension minimise UTA
5. wires are crossed vertically to maximise stability
5. secondary is designed offset to optimise beam while maintaining parallel vanes to minimise diffraction.
Below is an image of the pdf file attached for anyone who wants to build their own. If you print it on A1 paper it will be drawn to scale full size. 16inch-newTER.pdf 142.11KB 343 downloads