A big wooden GEM?
Posted 16 February 2011 - 07:24 AM
I will also ask this in the ATM forum, but I hope it is OK to also ask here.
I have sometimes contemplated getting a large refractor, but one thing that has kept me from getting one is the issue of mounting it. I will say right up front that tracking is absolutely essential to me. I sometimes observe tiny planetary nebulae at 800x - 1000x even with my 4", so a 6" or 8" will be used at even much higher powers. Stability at that kind of power is also extremely important. At 850x, which I've used, the true field of my 7mm ortho is just a hair over 3 arcminutes.
My personal preference is a german equatorial mount, both because it looks classic, but also because it has certain advantages for visual observing that I've come to appreciate, for example the ability to lower the eyepiece height when observing objects low in the sky away from the meridian by letting the scope hang from the dec axis instead of being on top of it.
But a large equatoreal mount is expensive if new and used ones here in Europe doesn't seem to surface the market very often at all and shipping a huge lump of metal from the US is out of the question.
I would therefore like to know if some of you have built or seen a big GEM made from wood? Plans would (!) be nice, but are not absolutely required. Ideas of all kinds are welcomed, especially on the drives and slow motion controls.
Posted 16 February 2011 - 11:09 AM
what do you mean by "large" - is the mount going to be portable ?
If not, consider the Michael Knopf MK-70 equatorial mount, which can be purchased (with FS-2 GOTO) for approx. € 8000,- from Astrolumina.
Weight of the head is 105 kg (but splits in the RA and DEC component), and will definetivly carry a 10" f/12 refractor. It uses friction drives, so no PE. All Knopf mounts were designed using the finite-element-method, so are optimezed for maximum stability. Only steel used, no aluminium.
All reports I've read are very positive.
I regard the price a bargain considering the payload capabilities of this mount (and the fact that it includes GOTO (which is a thing that has arisen your curiosity, right ?)).
Posted 17 February 2011 - 04:34 AM
I am a bit divided over the portability issue, but let's just say "no" for the moment. The reason I wanted something I could build myself is that I don't have € 8000,- for a new mount. Had I had that, all problems would have been solved in an instant.
Goto is not important for me.
The Knopf mount is impressive - especially for the price - but the funds aren't available right now.