Posts Made By: William Chang

May 6, 2005 10:23 PM Forum: Telescope Making

Schiefspiegler anyone?

Posted By William Chang

Maybe not a Schief, but a Classical Cass or Mersenne secondary? (Respectively hyperboloidal and paraboloidal, grind your own.)

If the primary were f7 or so, you could "fold twice" with an X% CO round secondary and same X% CO elliptical tertiary, for low eyepiece height. But that's not what you have.

-- William

May 9, 2005 02:38 AM Forum: Refractors

Refractor on a Stick (Lens testing)

Posted By William Chang

Keith, is the rear flange custom? I'd love to find something like that for my own SkyBeam/OpticalBench project...

-- William

May 9, 2005 03:09 AM Forum: After Dark

Burion 100F6

Posted By William Chang

Neat. Possibly "too late", but it would be instructive for us to see how the objective attaches.

I happen to be looking for a decent 4" f/6 objective too :-)

-- William

May 13, 2005 04:21 AM Forum: Beginning Astronomy?

Just a quick poll.

Posted By William Chang

I got hooked by the S&T Gleanings in the public library, and naked-eye views of Orion -- in 10th grade. Eventually ordered a Dynascope but waited almost a year for delivery. Took it out to see M42 under NY streetlights. Soon after, I left home (and the RV-6) for college. Ten years later, I bought one of the first 80f5 (Celestron SS-80) and ProOptic Plossls, but the purple halo around the moon was not good. Nearly another ten years later, I tried again with a Genesis and a Questar... and then a "classic" 8f6 Dob (made by our own Walt Hamler). Then I _really_ got hooked.

Now, I have too many telescope projects to list. The Genesis was sold in '03 (it is _right now_ making another appearance on AM), and the Questar Duplex was replaced by an Intes-Micro M615 Mak, Borg 100 Achro piggyback, NexStar mount/Ray's Bracket, Denkmeier II, etc (same $). This "AlterBorgRayStarDuplex" will also be joined by a Starmaster 12.5 ELT. And, still too many projects...

-- William (Saratoga, CA)

May 24, 2005 02:06 AM Forum: Beginning Astronomy?

with your significant other

Posted By William Chang

My wife will always come out to look (and help round up the kids too). Of course, she's not obsessive about the equipment like I am. She also has better "experiential momory" than I.

The meteor storms a few years back were really great. -- William

June 6, 2005 02:29 AM Forum: Investment Discussions

Long bond yield, comments???

Posted By William Chang

Maybe Fannie Mae is buying them up, along with all of the nation's mortgages.

Isn't the commodities "inflation" simply a reflection of the depreciated US$ against the Euro? Of course, the US$ is low because the Fed prints all the money that anyone asks for, including Fannie Mae.

June 14, 2005 05:43 AM Forum: Equipment Talk

My New scope?

Posted By William Chang

If it doesn't have to be truss, and you have a large budget, maybe one of the high tech Dobs:

Compact Precision Telescope (retractible OTA, foldable mount, world-class mirror cell)

Infinity Telescopes Uti (carbon fiber, extremely compact and transportable)

Plettstone (three-pole, Albert Highe design)

I have looked through a CPT with Royce 10". As for the Starsplitter -- I have the mirrorless body of a Compact II. It seems pretty nice except for the old style "pie mold" mirror cell. The sling mirror cell shown on Starsplitter site looks much better, but the extremely low price of the cell makes me worry a bit. My point is to shop for a mirror cell first -- it defines the maker....

Or buy a DAR Astro cell and Orion XTi, replace the Orion mirror/cell/focuser.

Just some random thoughts smile

-- William

February 3, 2006 03:46 AM Forum: TeleVue

Slo-mo for Gibraltor

Posted By William Chang

I have a Gibraltar that a previous owner modified -- the azimuth has a zero-friction needle bearing. If somebody has a slo-mo/clutch idea I'd love to hear it too.

However, I've long had the idea of inserting between a Gibraltar/TelePod head and the tripod, a barndoor-tracker-like equatorial adaptor. Basically, add wedges to the two barndoor tracker leaves so the top and bottom surfaces are (near) level. Or, think of a small box sliced and piano-hinged to open/rotate about the polar axis. I called that the Soapbox/TeleTrack but in old issues of Telescope Making a related design was known as "nested corners" equatorial platform. I don't have a TelePod head to play with though, and none has been available lately at a good price ($150).

Would you be interested in building a prototype or two? :-)

-- William (Saratoga, CA)




February 5, 2006 07:51 AM Forum: Equipment Talk

Fujinon 16x70 vs 4" refractor

Posted By William Chang

Hi Dave, I'll chime in here rather than reply to your email.

IMO the biggest drawbacks with binocs are (1) straight-through view aka pain in the neck, (2) fixed eyepiece/magnification, so you can't optimize for a given object or conditions (such as sky brightness). There are exotic binoculars (Apogee RA88 -- one was listed just yesterday) that more-or-less address these two issues.

In my own light-polluted skies, I've found that a magnification around 35-40X FOR ONE EYE really helps to darken the sky background, bringing out fainter stars and objects. In my experience, two eyes should enhance perceived contrast fairly significantly so 16X might be enough -- but I have not looked through a Fujinon. Another thing to note is that the Fujinon's EPs aren't nearly as wide and flat-field as your 24Pan. While I can spot open clusters with a nice pair of 10X binocs, the power is too low.

When I first learned the skies I was fortunate to have a TeleVue Genesis with its excellent red-dot finder. Sometimes 10-mile-distant San Jose would become fog-covered, making my sky dark enough to show (barely) the Milky Way. On those rare nights scanning the sky was FUN. I think my first such night I managed to find nearly all of the visible well-known open clusters -- in most cases seeing them for the first time.

A few months later, I ran into the limitations of a 4" scope: globular clusters and galaxies were no fun. I managed to buy an 8" Dob with an exquisite mirror (made by an Astromarter) and, on another good night, picked off most of the Messier globs and galaxies visible. (Orion UltraBlock filter definitely helped.) In a moment of weakness I sold the Genesis and still miss it. (Then at some point I got into binoviewing but that's another story!)

Nowadays I have a few projects, including Big Dobs and Binoscopes.

-- William (Saratoga, CA)

February 5, 2006 08:02 AM Forum: Takahashi

Small Mount for Sky90?

Posted By William Chang

Lukman, can you show how the attachment is made? Thanks, -- William (Saratoga, CA)

p.s. I have a 6" Mak mounted on a NexStar 8 single-arm fork with Ray's Bracket. I'm thinking of moving the dovetail clamp from the Bracket (bolted on) to the NexStar round plate directly (again by drilling and tapping two holes for the bolts). But yours looks a bit different (from this angle).