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Posts Made By: William Chang

August 26, 2003 02:11 AM Forum: Equipment Talk

2-inch Barlow under 2X?

Posted By William Chang

I'm aware of only the Siebert 1.5X 2" Ultra Barlow -- can anyone comment on it, or anything comparable?

I have 32mm and 17mm 2" eyepieces that I would like to Barlow -- but my 2X Big Barlow is no help, especially since I have 8mm covered as well. I might get rid of the 17mm but it's a Nagler T4...

Thanks in advance, -- William



August 26, 2003 02:22 AM Forum: Eyepieces

2" Barlow under 2X?

Posted By William Chang

I'm aware of only the Siebert 1.5X 2" Ultra Barlow -- can anyone comment on it, or anything comparable?

I have 32mm and 17mm 2" eyepieces that I would like to Barlow -- but my 2X Big Barlow is no help, especially since I have 8mm covered as well. I might get rid of the 17mm but it's a Nagler T4...

Thanks in advance, -- William

August 27, 2003 05:33 PM Forum: Binoviewers

Denkmeier StarSweeper with long-focus refractor?

Posted By William Chang

Would it work?? I'm thinking f/15 + SS, less color than f/8 Achro? Hmm...

-- William

September 11, 2003 10:25 PM Forum: Equipment Talk

Schmidt-Newtonian and high power?

Posted By William Chang

The Meade SN's are often praised (or put down) as RFTs. Is there a reason (quality?) why they aren't good for high magnification? (Besides collimation and C.O. issues which other scopes share.) Thanks,

-- William

September 12, 2003 06:23 PM Forum: Eyepieces

Best 10-12mm eyepiece?

Posted By William Chang

I have been scratching my head on this one...

Scanning reviews & postings, this range of focal lenghts seems to engender "top of breed" eyepieces in every line. What I mean is, the 10.5 seems to be the favorite among the Pentax XLs; the 12 Radian has the highest ratings within that line; Speers-Waler has a well-reviewed 10 and a 12 (or used to); Nagler has 11T6 (the T1 was highly sought after) and the big-lens 12T4.

Taking into account the usual measures including comfort (eye-relief, blackout), performance (contrast, sharpness, FOV), and weight -- is there a "best" among the best?

I have the 17T4 and Speers-Waler 5-8 (both about 80* AFOV) and would like to fill the gap. I sold a 13T1 because it was a tad too close to the 17; wanted a bit more power. I almost jumped on a 10.5XL (for its legendary ease-of-use) but in terms of FOV, the SW5-8 kind of covers it at 8mm (though it's less user friendly). So am I really just choosing among three TeleVues: 12 Radian, 12T4, and 11T6?

I'm also considering the Pentax 8-24 zoom; at 10-12mm the FOV is 50-55*, narrower than the 10.5XL but more flexible and almost as sharp. Yet another possibility is one of the new crop of ~1.6X 2" Barlows, with the 17T4.

Which of these super eyepieces would you rather have? (Only one please!)

-- William

p.s. I wear glasses, but at this magnificaion can usually do without.

September 20, 2003 03:59 PM Forum: Maksutovs

APM 5" f/15 Mak?

Posted By William Chang

As Phil noted, these have a small C.O. of only 27.5%. Chinese-made, built-in flip diagonal and axial port, only $300. Any good??

-- William


September 22, 2003 01:23 AM Forum: Maksutovs

Can a user collimate ETX 125?

Posted By William Chang

I just read a report of an out-of-collimation ETX straight out of the box. Assuming it is impractical to send it back to Meade, can a (non-expert) user expect to collimate it?

I also just found the following including a warning from the esteemed Dr. Sherrod that users shouldn't try to collimate their Maks (ETX in particular).

http://www.weasner.com/etx/warnings/collimation-warning.html
http://www.weasner.com/etx/techtips/collimating.html

Comments anyone?? If true then non-experts should stay away from Maks that aren't covered by a factory warranty, including those sold on Astromart! (Can also lose collimation during shipping.) Sounds pretty drastic.

The Meade Schmidt-Newts also have a reputation for being hard to collimate (and not hard to lose collimation)...

Whereas the SCTs seem to be designed to be collimated by the user. Why is there such a difference?

I'm considering getting a custom ETX (out of warranty). Any advice will be greatly appreciated,

-- William

p.s. I can collimate a Newt :-)


November 28, 2004 03:59 AM Forum: Telescope Making

Classical Cassegrain optics?

Posted By William Chang

Does anyone know where I can find 8" or so aperture Cassegrain optics? (Got one hiding in a closet? :-) Thanks, -- William

December 5, 2004 12:53 PM Forum: Equipment Talk

Focuser for 7" OD Newt?

Posted By William Chang

I would like to change the 2" focuser on my Meade SN-6, but I can't find a decent one that's designed for such a small tube diameter. (JMI's 1.25" RCF has a 7" OD base but not the 2" one.)

Ideally, I'd like one with ~2" travel, and be relatively low-profile -- for DenkII binoviewer without OCS. (I'd stack extension tubes for mono. The focal plane of this scope is a whopping 6.5" outside the tube.)

Any suggestions will be greatly appreciated! -- William

December 6, 2004 09:00 PM Forum: Telescope Making

Mersenne-Gregorian?

Posted By William Chang

A la Clyde Bone's Mersenne telescope with "neutralizing" convex parabolic secondary (S&T 9/99) directing collimated rays to a refractor, what about the Gregorian configuration -- concave parabolic secondary with coincident focal point as the primary? How much aberration off-axis? Does anyone happen to have done a ray-trace or have good intuition how well it would work?

Thanks, -- William

Note added: Guess what -- just found Vlad's one-week-old (!) message in the ATM List: (my interpretation) the coma will be worse by 1/obstruction, astigmatism by 1/obs-squared. Ouch.