A question asked me in a recent email seemed rather important so I thought I'd post my answer to the list in case anyone else was working on a parallelogram. Namely, how long to make the arms? A few things to keep in mind: You want to be able to view directly overhead when standing, without having to "scrunch down" at all. Any kind of stooping to get under the binocular when it's pointed overhead will cause muscle fatigue and strain, and defeats the purpose of the parallelogram. I also like to add a few inches for folks a bit taller than I am. I'm 5'-11" in my shoes, but I have good friends in the 6'-4" range so making it tall enough for them as well is a nice gesture. All of the height doesn't have to come from just parallelogram arm length. Excessively long arms will lead to an overly-long damping time for natural oscillations and vibration inherent in cantalevered or balanced structures. Some of the height can be achieved with the tripod or post it is mounted on. But also consider those times when you want to observe seated or reclining in a lounger- the arms can't be so short that the binocular can't reach low enough. Again, the tripod can help by being adjustable to this lower limit, but it is a nice feature if most, if not all, of the minimum-to-maximum height range can be accommodated with just the parallelogram arms themselves. At least try to maximize this range and then leave the remainder for an adjustable tripod, if necessary. Sometimes at star parties I will set up two parallelograms, one for a greater height reach than the other, to accomodate everyone without having to re-adjust tripod legs in the dark. Back to chair or lounge observing for a moment. If using a parallelogram for this style of observing, it is mandatory that the design have pan capability right at the binocular, and not be completely reliant on the central pivot atop the tripod for azimuth changes- otherwise your chair had better have casters because you'll be constantly rolling around the tripod to stay under the binos. Hard to do in the field in most cases! I suppose you could set your chair on a mechanics "creeper", on a concrete surface, otherwise design-in some pan capability at the bino end of the arms. Hope this helps. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com