Ha ha ha ha.... (maniacle laughter) You've fallen into my cunning trap - now I get to spout on about my latest obsession with a clear conscience!
OK, if anyone wants to investigate the wonderful properties of Tilted-Component Telescopes, you should do a Google search for "Wierd Telescopes" and download WinSpot32.exe (a small app) from Dave Stevick's web page. There are many TCT designs included in the download, including an f/10 Folded Stevick-Paul. I have uploaded my f/15 design to my subdirectory in the temporary files section of this board. Download them and remove the .txt extensions and load them up with WinSpot32. Fiddle and play to your heart's content.
the files are at:
www.irishastronomy.org/user_resources/fi...71-FSP138f15a.sp.txt
and
www.irishastronomy.org/user_resources/fi...607-FSP138f15.SP.txt
one shows the normal folded layout and the other includes an additional flip-down mirror to bring the focus to a convenient location for viewing high altitude objects.
When you load up each file, click Focus then Plot Standard, then Airy. The central dot is the on-axis bundle of rays, and the four slightly larger blobs at N, S, E & W are the off-axis bundles focused for 0.25 degrees off axis (0.5degree unvignetted field of view.) The circle represents the maximum allowable size of the Airy disk. Anything bigger than this circle means that the image is not defraction or aberation limited. As you can see, the Folded Stevick-Paul design falls waaaaaaay inside this criteria. No spherical aberation; no coma; no astigmatism, and as it is a reflector, no chromatic aberation! I'm hoping that this unobstructed design will make a planetary telescope to knock my socks off with!
If anyone wants to compare the spot diagrams for a standard Newtonian or a Classical Cassegrain, I think I have those files somewhere.
How long is it going to take to complete? Weeeeell... that rather depends on my arms and stamina in general! At present, I am managing to get about 2 hours work in every evening before I pass out in a quivering heap. Polishing out a 6" or 8" mirror is easy. Polishing out a 14" is *much* harder work! There is considerably more resistance and consequently more effort is needed... and for much longer!
So far I have put in about 10-15 hours of polishing on the 14". I reckon it will take about another 5-10 hours to polish out and fine tune the radius of curvature to the +/- 0.5mm tolerance I have set.
I then have to polish out the three 10" flat disks and test them against eachother by interferance to get just one master flat. I then have to re-grind the remaining two 10" disks to become a matching pair of concave and convex sphereoids and polish them out. Say 10 hours grinding and 10-20 hours polishing. The two sphereoids also have to be tested against eachother by interference and polished to match. I don't look forward to that... or making the flat.
The tube, cells, tilted focuser and mounting are positively trivial tasks compared to the optical work, but I am hoping to have the whole shooting match finished by... er... sometime around Christmas (though I'm not going to say which one!)
Good grief, I don't believe I just set such a deadline! Now I'll have to try and keep on track or have my grandiose claims come back to bite me on the ass and generally haunt me!
Phil.
PS - I was driving home tonight over the Wicklow Pass near Laragh and stopped to take a pee(k) at the sky. The Milky-Way was stunning - you just don't see the sky like that from Bray anymore. Is anyone doing observing sessions these days either in Cloon, Djouce or in Wicklow in general? I *need* to get back out under the stars before I forget my way completely!
  