Proto-star curved secondary holder

I'm working on another scope, an 8" f6. I'm trying to decide which spider/secondary holder to use. I'm looking at the Proto-Star curved holder (really "U" shaped, www.fpi-protostar.com/curved.htm ). Has anyone got any experience with this? I'm concerned that it would be difficult to adjust collimation (hard to center accurately in the tube) and that it would not hold collimation well. Maybe the 3 vane spider would work better and still have less diffraction than a four vane. Any comments would be appreciated. Thanks

Dave Burtrum

I made a curved spider for my 8" F/6. No matter how I made it, you end up bending the curve to get it collimated well. If you read the technical pdf documents on the protostar spider, at the very end of installation, they recommend the same, bending it to get it just right. Also the stability of a curved spider has the potential of not being as good as a straight vane style since the mirror holder is not under tension, so you possibly can get a springy effect when moving the tube. Concerning the diffraction, you still could see the curved vane diffraction at low power on bright objects, but at high power (where it really matters) the diffraction was invisible. So that is my experience, yours and others may vary....