Posts Made By: William Chang

Holy Cow! I'm speechless :-) -- William

Well, a folded 6" f/15 is potentially a travel scope, and would be stable on a much smaller/cheaper mount, compared to a straight-tube f/12. If I can get my hands on an objective I would do it :-) I would use a reasonably priced high quality 3" first mirror instead of 4". On the other hand, a 6" f/8 with Chromacor is much easier to own. Good luck with your project,

-- William Chang (Saratoga CA)

Would there have been material difference, if you had included 8" SCT, plus 6", 11" and 14" Newts in the mix? Does Aberrator really care :-)

-- William

Keller makes maple plywood drum shells and cylinders (available from Anderson Internation Trading). The cylinders are sold in lengths of 27", 48" and 96" (exotic veneers available); the drum shells in various sizes. I'm considering a 13D 9L drum shell for the secondary cage of an 11" f/4.5 former StarHopper. Thickness goes up to 10-ply, 0.27" for the 100% maple drum shells, up to 7/16" for cylinders.

Has anyone any experience with these plywood tubes, or general comments/suggestions?

-- William

If you get JMI Wheelie Bars and Lymax Cooler for the NS11, you might find it easy to use (e.g. seeing Mars in early morning). I don't have this setup but did research on it (waiting for the right opportunity to own one :-) Folks on SAA recommended this scope when I asked for aperture fever remedy under serious light pollution.

The FS-102 duplicates the TeleVue; you can mount the TV on your GM-8. Or get a Chromacor'ed 5" or 6" refractor, or a 6" Mak-Newt. Wheelie Bars may also come in handy here if the scope is near the upper limit.

-- William

I haven't built any (see the other thread). I did get a Meade SN6 ($200) to try "over the shoulder" bazooka-style. A star diagonal redirects the light along the tube axis, but I was thinking looking UP rather than down. If this works, a twin-tube alt-az mount (Giro??) -- or a yoke as you suggest -- can be positioned behind the recliner etc. Or it could be a mobile unit :-)

-- William Chang (Saratoga CA)

Very ingenious! What's the dimension of the "cube"? Please post a report! -- William

Thanks Mike, this is fun to play with. I can't remember the "formula" (or plot) of the number of stars of a given (sub-)magnitude -- does anyone know?

(MATH ALERT)

In principle, one can define a "Richness of Field" function:

RF(visual magnitude limit, aperture, magnification)
= expected number of visible stars in the FOV

possibly normalized for maximum exit pupil (7mm; it could be a function of visual limiting magnitude and observer's age) and eyepiece AFOV (say 60*), and possibly other factors such as elevation, humidity, angle, etc.

Then, for a given visual magnitude limit, one could look for the combination of aperture and magnification that maximizes the RF() function, and call such a telescope a Richest Field Telescope -- RFT. My gut feeling is that the visual limiting magnitude is a major determinant in "scoping out" the RFT aperture/magnification -- i.e. different scopes under different skies.

In the extreme of dark skies, the unaided naked eye (7mm aperture, 1X power, 60* FOV) may come pretty close. But near cities (or under full moon) there are few naked-eye stars, so one needs extra aperture/magnification to darken the FOV background -- in order to see more stars. Using the calculator, I found the L.M. difference between 16X and 38X for a 4" refractor (and 40-year-old-eyes), to be 1.2 for mag-5.5 sky, 1.5 for mag-4 sky, and 1.7 for mag-2.5 sky. Higher magnification helps more when the sky is bright.

Plugging in the star-count as a function of magnitude, one ought to be able to figure out which telescope or binoculars is "RFT" under a given limiting magnitude. Does this make sense to anyone?

-- William Chang (Saratoga CA)

There must be a Dremel tool/bit that would work. Or the "drill saw" that cuts with a bit -- have you seen that? Or you can just drill lots and lots of holes...

I designed a three-part interlocking tube that collapses to about 20", and one of these days will order a suitable plywood drumshell and give it a try. I did see, and consider using the plastic tube you've got, but even cut in three it's still heavy -- the wall is just too thick.

How about using it as a backyard pier?

-- William Chang (Saratoga CA)

Regarding vibration: are you using suppression pads? They make a huge difference. My old Panoramic (delrin sleeve azimuth) is unuseable without them, perfectly steady with them. That said, my new used Gibraltar (fancy) azimuth wiggles when I focus. How do you adjust it so it doesn't?

It can't be that hard to add azimuth slo-mo: have the eyepiece caddies "walk around" the flat round base on rubber rollers, if you think about it... Better yet, I have a design for a barndoor-style equatorial adapter (!) that would go in-between a TelePod head and the tripod. Unfortunately I don't have a TelePod so will probably try it out on a Giro first.

-- William Chang (Saratoga CA)