Posts Made By: William Chang

How black is your black?

How soon will the colors visibly fade?

Is color-laser blacker and/or more archival than inkjet?

Thanks, -- William

It takes at least an extra 15-20 minutes at the P.O. to ship overseas, not counting the extra packaging effort of maximizing protection while minimizing weight ($6 if it crosses over to the next lb). Hence I can perfectly understand why a business charges a hefty service fee for overseas orders.

I have sent many premium eyepieces overseas, with the following conditions: PayPal with fees (now 4%), fully declared and insured Global Express Mail (EMS). And, I try very hard to make sure it fits the buyer's needs, and to describe the condition fully. Given the recent US$ devaluation, I guess it's still a very good deal for an overseas buyer.

The only non-EP I've sent overseas is a Questar -- again high value, relatively light weight. Only cost $100 EMS with a fair bit of thorough (and inventive) packing. Shipped on a Friday, received on Monday (still Sunday in the US!).

-- William

I haven't been too lucky with UPS lately

A couple weeks ago a Unitron #142 3" equatorial mount came with the mounting bar (where telescope cradle attaches) snapped in two. The material is some kind of cast aluminum that AFAIK precludes welding. My plan of attack is to use JB-Weld, then reinforce the mounting bar with an aluminum splint. (I have since learned of three other people who had encountered the exact same problem!)

Then yesterday I took delivery of a "red tube" Edmund 6" equatorial. Alas, the finderscope mounting rings were knocked off the tube, each taking with it a piece of about 1"x2" red tube material, some kind of laminated/ply phenolic resin. Structurally I don't think there's a problem, so I'd like to glue the pieces back as unnoticeably as possible. (And I've also heard that the red phenolic tube isn't the hardiest.)

PLEASE recommend adhesives or procedures for either of these repairs!

These are actually my first two GEMs, not counting the Criterion RV-6 Dynascope I had ordered in high school, that was delivered a year later just when I left home for college -- so I never really owned it. Neither the Unitron/Edmund had been in "collectible" condition, but I still hope to repair these vintage scopes and put them to good use!

Your help is appreciated,

-- William Chang (Saratoga, CA)

I haven't been too lucky with UPS lately.

A couple weeks ago a Unitron #142 3" equatorial mount came with the mounting bar (where telescope cradle attaches) snapped in two. The material is some kind of cast aluminum that AFAIK precludes welding. My plan of attack is to use JB-Weld, then reinforce the mounting bar with an aluminum splint. (I have since learned of three other people who had encountered the exact same problem!)

Then yesterday I took delivery of a "red tube" Edmund 6" equatorial. Alas, the finderscope mounting rings were knocked off the tube, each taking with it a piece of about 1"x2" red tube material, some kind of laminated/ply phenolic resin. Structurally I don't think there's a problem, so I'd like to glue the pieces back as unnoticeably as possible. (And I've also heard that the red phenolic tube isn't the hardiest.)

PLEASE recommend adhesives or procedures for either of these repairs!

These are actually my first two GEMs, not counting the Criterion RV-6 Dynascope I had ordered in high school, that was delivered a year later just when I left home for college -- so I never really owned it. Neither the Unitron/Edmund had been in "collectible" condition, but I still hope to repair these vintage scopes and put them to good use!

Your help is appreciated,

-- William Chang (Saratoga, CA)

I don't have an 8" SCT but...

Linton & Mark already gave the "by the book" answer, ~20mm that would give you 2mm exit pupil and 100X, pretty much the ideal all-around magnification for diverse DSO.

Personally however, it would be the spectacular 12mm Brandon, which is very inexpensive when you can find a pre-owned one (a couple times a year). This magnification (167X) is ideal for planets, planetary nebulae, and globular clusters -- after all the SCT's forte! -- so it would become the VIEWING eyepiece (as opposed to finding or scanning). You wouldn't like the Brandon's FOV, but after one look you also wouldn't care

I would not recommend a zoom because their widest AFOV typically occurs at the high-power end. So the great 8-24 Pentax XL at 8mm gives 250X (60* AFOV); at 12mm its AFOV is still quite respectable, but at 20mm it's down to about 40*.

-- William Chang (Saratoga, CA)

I have M13 through a Royce 10" f/6 indelibly etched on my retina -- wondering if there's a chance I might be disappointed by a (much more convenient) f/5. Not worried about collimation, but rather field curvature. Any thoughts? Thanks,

-- William

p.s. I do have a Paracorr but it has trade-offs; prefer to not need it.

I learned the sky with a Genesis which I unfortunately sold a few years ago. Luckily, I will be getting a TV102 with (basically free) TelePod and 22 Pan, 7/5 Monos. Would you guys recommend a fine focuser upgrade and/or OCS for the DenkII? What else? Any tricks to stiffening the tripod legs? Thanks everyone,

-- William

I learned the sky with a Genesis which I unfortunately sold a few years ago. Luckily, I will be getting a TV102 with (basically free) TelePod and 22 Pan, 7/5 Monos. Would you guys recommend a fine focuser upgrade and/or OCS for the DenkII? What else? Any tricks to stiffening the tripod legs? Thanks everyone,

-- William

I have made some drawings (in the style of All About Telescopes) that show the geometry of the Amici RACI Prism and corresponding mirror implementations. Derivations include: cross sectional area and light-path for parallel, horizontal rays; angle of incidence; shape and rotation of the reflective area for a circular bundle. I will add explanations later.

As can be seen, several mirror-based implementations are possible, in addition to the commercial EMS system which utilizes two 60* elbow joints.

Roof cross-section angle alpha ~ 70.53*
Angle of incidence = 60*

Enjoy,

-- William Chang (Saratoga, CA)

Wondering if there's a BV optical design that is already Right Angle, for refractors of course. Buried in microscope literature perhaps?

-- William