Author Topic: 10" Planet Killer  (Read 141 times)

adpotabza

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10" Planet Killer
« on: December 24, 2017, 06:35:15 PM »
I figured I should start a thread with this as I actually now have sufficient money to get it done.  I have been mentioning this layout for some time.

As many of you know, I spent the end of May and beginning of June this year making a 6" f/6.5 mirror, which is presently a wonderful half-polished sphere.  It sits in my garage stuck into its pitch lap which neglects to unstick despite all efforts (probably because I was using Burgundy pitch which I added too much oil back in to revive, worked in a popular garage, and did the wrong things to try to divide them).  The failure of this project not only cost me $100 and something like 60 hours of my entire life, but it also greatly discouraged me from making yet another mirror.

Not trying again would be a waste, however.  I finally have a fairly well cleaned-up garage, a Foucault tester, and also a fair amount of understanding of the topic.  I would like to try to make another, not simply to prove it could be done but also because I really could commercialize this.

As opposed to make another 6" (I have a 6" f/8 Newtonian I pretty much never use thanks to my 8" SCT), I have decided I have enough experience to produce a 10".  I did achieve a wonderful sphere and I had gotten through a sizable chunk of polishing on both", so provided figuring isn't too hard I think I could do it.  Slower 10-inchers are done by first-time mirror manufacturers, and I am at least a bit more knowledgable than the usual first-time mirror manufacturer.

I'm going to be planning for a 10" f/7-8.  Optically, this layout will allow for pretty much no coma, a 20% or smaller central barrier, and effortless collimation.  I am tall enough (6' now, probably 6' 6" or more in the future) which I will need no more than a short step stool for viewing, even in the zenith.

The mirror blank, along with probably the secondary, spider, and focuser, will be gotten in Stellafane after this month to save money.  In the meantime I will start the construction of the range itself, along with enhancing my "optical shop" so it is somewhat easier and more comfortable to use.

The layout for the range is to use a mirror box in the back like in a truss Dob, but with a good tube rather than trusses, similar to the larger scopes produced by John Dobson himself, or even the Odyssey Blue Tubes (albeit with considerably thinner baltic birch plywood).  This will allow for easy, no-tools removal of the primary for analyzing (I hope to star test and Foucault/Ronchi examine the mirror when possible), and also effortless spinning of the tube.  The mirror will rest on a strap and also be held by 2 pieces of timber (like Dobson's first scopes) during testing but I will use glue to attach it into the mirror cell when that's done.

The tube itself will be Sonotube, but having an interesting quirk.  Since Sonotubes are not available to me in lengths of over 48", I will need to place two tubes together.  The method that I plan on using is basically exactly the same as the sole posted by Jthompson, using a marginally smaller upper tube that fits within the lower one, fastened by bolts.

The scope will be able to fit in a car and so make occasional excursions to dark heavens and astronomy classes/outreach events, but this isn't its principal purpose.

I plan on using it on an EQ platform for outreach and planetary imaging.  I may make or buy one, based on what I could afford.