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Posts Made By: William Chang

September 20, 2003 03:38 AM Forum: Telescope Making

Double scopes

Posted By William Chang
Hi Robert (and Ed). I went to the trouble of obtaining a pair of Celestron SS80 f/5's and straight-through porro prisms (which were _very_ hard to find inexpensively), and designing a co-collimatable mounting system to align the scopes. The two porro prisms bring the EPs to within the normal IPD. Alas, they would not reach focus, so I need to either shorten the draw-tubes or find a shorter "collar ring"...

If money were no object, just get a pair of premium porro-prism spotting scopes and mount them +(O O)+ if you know what I mean. The challenge is to maintain perfect co-collimation at high power, with an eyepiece assembly that allows easy IPD adjustment.

If each scope were left-right reversed but top-down correct (refractor + star diagonal), you will get what's called pseudo-stereo on terrestrial objects -- a basketball will look concave :-) Astronomically it's not supposed to make a difference due to the great distance involved, but I haven't convinced myself of that yet ;-)

-- William

p.s. By the way, my mount design looks like O/\O where the left scope pivots on the / slope, and the right scope pivots on the \ slope, of the aluminum angle. The two scopes can be adjusted along orthogonal axes for co-collimation.

September 20, 2003 06:39 PM Forum: Equipment Talk

EPs with built in barlow vs separate barlow

Posted By William Chang
Has anybody tried Rick Blakley's Uranoport "screw-in" recessed Barlow?

(Rick, perhaps you would like to comment?)

I personally find it hard to resist interesting optics, and may try to get one to compare with (1) long Barlow, (2) short Barlow, (3) Barlow optics screwed into the filter threads, and (4) EPs with built-in Barlow... What would be a good test set?

-- William

September 20, 2003 11:11 PM Forum: Chinese Optics Imports

Update from Bill, When?

Posted By William Chang
Sigh. Couldn't a few random production units (_real ones_) have been flown in before the rest got on the boat?? Q/C is a statistical science -- presumably Bill Burgess had earlier tested multiple samples of the optics and was satisfied -- hence jumping to the conclusion the later broadband coatings must have been responsible for the problem... Now if all he tested were the pre-production units, this could be a problem.

I recall reading somewhere Orion only had 25 units of the 80ED. Pretty scary way of doing business -- if true.

-- William

p.s. I'll take someone's spot for a 1278.

September 24, 2003 06:12 PM Forum: Meade

10" Schmidt-Newtonian coma problem

Posted By William Chang
I'm no expert but I've read the Schmidt design "merely" reduces coma by half, so the (unuseable) f/4 coma is corrected to more like f/6, i.e. still present but useable. (I have the SN6 f/5 which is pretty good coma-wise.) That said, given the superlative astrophotos done using the SN's, it's quite possible your scope may need some work. However, re-collimation of the SN is supposed to be a pain and some people eventually gave up and shipped their scopes back to Meade (so try not to void the warranty). Maybe if you used CCD the corners/coma wouldn't be a problem?

-- William

September 25, 2003 08:40 PM Forum: Eyepieces

Opinions Wanted: Ultima 30mm or 35mm?

Posted By William Chang
Peter, since you have the 24mm (envy of the world :-) the 35mm makes more sense. You might look up my long posts from a few weeks ago, and the respective threads. This seems to be a FAQ!

http://www.astromart.com/messages.asp?message_id=116817

http://www.astromart.com/messages.asp?message_id=103983

Also read the following regarding "Ultima 30mm tight fit" (which I can confirm with my _two_ independently obtained samples -- solution: replace the chrome barrel).

http://www.astromart.com/messages.asp?message_id=109219

The 35mm is often cheaper on AM than the 30mm.

Clear skies, -- William

September 25, 2003 08:54 PM Forum: Binoviewers

Stupid Question?

Posted By William Chang
Re: collimating with or without diagonal/binoviewer in place

If the diag/bv ever needs to be rotated (GEM, Dob) then the draw-tube has to be true. If the scope is an alt-az SCT with moving-mirror focus and optically stationery diag/bv/ep assembly, then either way should be fine.

-- William

September 28, 2003 01:47 AM Forum: Refractors

Small Refractor for Wide Field and Planetary?

Posted By William Chang
Well, the TeleVue 4-inchers have been showing up a lot on AM -- suits any budget. I think they are all fine on Wide Field, and on planets you may see a very slight pale ring arount moon and Jupiter (I wouldn't exactly call it "color" but technically that's what it is). You'll have to decide how little of it you can tolerate. While these are not airline carry-on like the Traveler, I think they'll go into a suitcase just fine -- wrapped in a foam camping mattress or something.

Or the Borg -- why not the 100ED? I believe these come up once every few months and one sold recently for about $1600 with a bunch of extras. It's _very_ compact.

-- William

p.s. I use a Genesis on the Panoramic mount at up to 270X.

September 30, 2003 06:03 AM Forum: Equipment Talk

Good focuser for a dob?

Posted By William Chang
I have a Phase4 from AstroSystems; it has a synthetic base so is pretty light (for specs see www.astrosystems.biz). However, I have not installed it yet so cannot give you a first-hand report. I'm sure Ed Taychert can, since he sells it with his Tscope. It's low-profile if you countersink the base part into the focuser board, otherwise not particularly so despite the spec. (I know where you can get one used if you want one; search the Ads.)

As for nesting -- the FT detaches right? (I went through this "calculus" not long ago.)

-- William

October 2, 2003 03:42 AM Forum: Telescope Making

apple ply versus baltic birch

Posted By William Chang
I thought ApplePly is more like 3-4X Baltic Birch in price, after special freight (from www.aitwood.com), and cannot be purchased pre-cut or in smaller sizes. Whereas BB is available pre-cut and UPS-shipped. I even posted a wanted ad for small/scrap ApplePly, and recently someone else did the same...

ApplePly is supposed to be lighter.

-- William

October 5, 2003 05:54 PM Forum: Equipment Talk

UO Orthos Overated?

Posted By William Chang
My 2 cents... the 12.5 Ortho is unique in having both a simple design and decent eye-relief (around 10mm). I can (just) use it with thin glasses. The 12.5 Ultima by comparison has about half the eye-relief; the Plossl is somewhere in between, but definitely less than the Ortho.

-- William

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