I would tend to cut long and, if necessary it won't be a problem to shorten. If you're always going to use the diagonal, I'd set it up with a 6mm EP (or whatever EP that you know of to be the shortest focus point that you know of) to be near the bottom (about 1/2" from) the end of travel. If you plan on removing the diagonal for some viewing, do the min. height for that setup (recommended). The best way is to setup the lens on a support and look at something far away. My 200"fl refractor has a definite focal shift for anything under a mile distant so beware. The 6" focus range is probably acceptable for use with a diagonal that you may remove. The problem with answering your question is that all of the different EP's focus plane is different, even within a particular manufacturers line there can be major differences. Cut the tube long and do a final cut after everything else is done and you can verify the cut. You can imagine my pucker when I cut the wood of the tube for my 200"! You don't do that lightly.

• Re: Tube length - Josh_Miller/">Josh Miller - May 23, 1999 - 00:11 UTC