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Posts Made By: Dan D DuBal

May 23, 2003 10:05 PM Forum: Solar System Observing

TV-102 detected Jupiter phase - fact or fiction?

Posted By Dan D DuBal

Well, Ron, my night sky was mostly clear, but the seeing was fair at best (moderately "thick" laminar flow). I thought I *might* have observed "something going on" along Jove's trailing limb, but it could just as easily have been illusory. Just too wide a margin for error.

I'll try again, tomorrow night.

Meantime, I'll set my alarm for 4am (MDT) and hope my southern vantage is clear and the seeing good. Around that then, Syrtis Major will be quite major indeed. Besides, Mars's 87% illumination will be a bit easier to discern :-)

Cheers.
-Dan

May 28, 2003 07:11 AM Forum: Equipment Talk

Galileo 90mm Mak-Cass

Posted By Dan D DuBal

Not sure who makes it. I *do not* believe it's Synta.
Apogee once sold the Galileo Maksutov.
Opticmall currently sells it.

I have the Photon Instruments version of this Mak (which actually pre-dates the Galileo version), purchased some three years ago. My sample is overcorrected to a level *greater* than 1/4 wavelength (i.e., it's not "diffraction limited"). Mine's right at 1/3-wave. I've yet to hear of any stellar samples of either the Galileo or the Photon, but (admittedly) I haven't been *looking* for such reports/reviews, anyhoo.

If you're looking for a viable alternative to the ETX 90 -- one which has good-or-better optics for astronomy -- I myself would suggest you avoid the Galileo. However, that's based *only* on my own experience with a single example of the Photon.

On the other hand, if you're looking for a decent long-range terrestrial scope with closer-focus capabilities (which was what I wanted in the Photon), then the Galileo may fit the bill just fine.

Hope that helps a little. If any ??s, don't hesitate to ask.
Best wishes.
-Dan

May 29, 2003 07:05 AM Forum: Equipment Talk

Does this exist? Should it?

Posted By Dan D DuBal

The Terra Hoc and Star Hoc 90mm refractors (1000mm f/11.1) utilize 2-inch focusers and are available through Hardin Optical (Canada).

The 90mm achromat has always suffered a sort of "middle child" reputation, due to two important factors:
-size/bulk
-price/cost
In a nutshell, there isn't much difference between most 90mm achromats and 100-102mm achromats -- whether we're talking aperture, overall size/bulk, or price.

The "good side" of this minimal difference:
A good 90mm achromat can perform at a level quite near that of a good 4-inch achromat.

The "bad side" of this:
A good 4-inch achromat can be purchased for about the same price as a good 90mm achromat -- oftentimes, *exactly* the same price.

So, the customer's question becomes, "Why not just get the 4-incher? It's really not much bigger, and they cost about the same."

Indeed, most potential buyers do just that: opt for the 4-incher. Others go for the $$ and bulk savings and choose an 80mm achromat (which, itself, performs very similarly to a 90mm achromat).

The second-hand market does include some interesting 90mm achromats from the past, including rare birds such as a Vixen 90mm f/15. It's always a kick when those goodies show up on Astromart.

Best wishes.
-Dan

June 2, 2003 08:47 AM Forum: Deep Sky Observing

Best 10mm EP for Deep Sky Observing?

Posted By Dan D DuBal

What's your Newtonian's focal ratio? Would this eyepiece be "dedicated" to this scope, or would you be looking for maximum performance with other scopes, too?

Cheers.
-Dan

June 18, 2003 11:51 AM Forum: Equipment Talk

Info on Cheap Ultrawide Knight Owl eyepiece

Posted By Dan D DuBal

Hardly.

You can purchase the BW Optik 30mm from Anacortes for $94.99, and Herb can vouch for whether or not the BW has filter threads (it does).

The Knight Owl doesn't mention filter threads. Makes me wonder.

By the way -- please read "Terms of Service" "Message Board Useage Policy" regarding both hot links *and* the particular source for the link you posted.

Cheers.
-Dan

June 22, 2003 11:20 AM Forum: Equipment Talk

everbrite diagonal

Posted By Dan D DuBal

Hi Paul.

You might be seeing a decrease in reflectivity in the >20-yr-old aluminum coating. If able, try comparing your diagonal to a friend's newer one. A well -aligned & -coated prism diagonal will also yield a fair comparison, as its efficiency should be 95+%, too.

Is the extra bit of reflectivity worth the extra $$? That's a subjective decision -- only you can answer it. Based solely on your own brief description of what you experienced: "slight dropoff in brightness" (not even certain it was true), & your experience level (>20 years), I *will* dare to presume this: any well-made diagonal with a smooth, flat, 90%+-reflective mirror (not necessarily 98%) will show you *all* your eyes & your C8 can see. In terms of actual discernibility, we're talking about super-subtle threshold stars & barely-perceived differences in details &/or brightness. If you are one who spends most of his/her viewing time out there at the limits of visibility, then maybe the extra smidge of reflectivity is worth the high $$.

However, there *are* factors beyond reflectivity to consider. Some are purely subjective (which is allowed, after 20+ years of viewing!). Some are:

1. The A-P, Tele Vue, & Lumicon dielectic coatings are *extremely* durable -- significantly moreso than typical hard-overcoated aluminum.

2. Their reflectivity *does not* lessen with age, as they are completely dielectric (non-metallic). Even protected aluminum will eventually oxidize; peak reflectivity will lessen over years (though nowhere near as quickly as with unprotected aluminum).

3. Assuming one starts with an extremely smooth flat, the high-end multi-layer dielectric coating process will indeed yield a smoother mirror (hence a slight advantage in scatter & resulting contrast) than possible via aluminized diagonals. Of course, this begs the ??: how visible is this advantage? Unfortunately, that depends on factors such as visual acuity, seeing conditions, atmospheric scatter, inherent brightness of objects observed, telescopic system itself (accessories, too). For me, the "less scatter" consideration was less important when I purchased the A-P Maxbright. But that's just me.

4. Aesthetics. The Maxbright is beautiful. Finish is wonderful, & it exudes precision & quality. (See? I told you subjectivity/aesthetics may be a factor!) Of course, the A-P is a 2-incher, & you may prefer the 1.25-inch format (a sound option, considering its long f/10 ratio).

Personally, I'd have no qualms buying any of the the high-end 1.25-inchers from Tele Vue, Intes, or Lumicon.

All my babble may not have helped a bit. :-)

Best wishes & luck.
-Dan

June 22, 2003 08:55 PM Forum: Equipment Talk

Danger Will Robinson!

Posted By Dan D DuBal

Yikes! Glad to hear concrete was kissed.

For those wondering: my own 2-inch Intes extension (both upper collar and lower barrel) is machined from *one* section of alloy and is black-anodized throughout -- aside from the infamous Intes textured matte powdercoat finish on the outside of the upper collar). Over the years, Intes has offered very little in the way of chrome finish on any of their accessories.

Best wishes and continued luck, Barry.
-Dan

June 25, 2003 07:20 AM Forum: Equipment Talk

Best filter for Mars..

Posted By Dan D DuBal

Hi, John.
I usually observe without filters, but here are three that I have used in the past. These would be my own first choices for Martian surface features:
(in no particular order)
#15 yellow
#21 orange-red
Baader Planetarium Sky Glow

Of course, your question just triggered my curiosity, so I'll likely give these three stooges another run. :-) I'll report back with my impressions...

Best wishes.
-Dan

June 25, 2003 09:39 PM Forum: Eyepieces

worth upgrading Meade 4000 for planetary?

Posted By Dan D DuBal

I would consider any potential performance "improvements" yielded by Tele Vue plossls and/or Ultrascopics/Maximas/Gold Plossls to be subtle at most -- particularly at lower magnifications (i.e. ~15-50x). Longer scopes, such as an 8-inch f/10 Schmidt-Cassegrain, would yield magnifications in the 80-100x range -- certainly a useful range, particularly with Luna. Still, differences would likely be minor at most. Minor enough that average seeing conditions (atmospheric turbulence) would likely erase or "hide" any differences from the eye, anyhoo.

If you're able, try and locate a fellow stargazer with one of those longer Tele Vue plossls or Ults/Maxs/Golds -- take a test drive and compare. *That's* going to provide your own best evidence.

If I were in your shoes, I'd be *quite* tempted to replace both the 20mm and 26mm Meades with a single wider-field eyepiece, such as the 23mm Axiom, 24.5mm Superwide, or the 24mm UO Konig (big $$ advantage over the other two). -But that's just me. :-)

Best wishes and luck.
-Dan

June 29, 2003 08:34 PM Forum: Eyepieces

5 or 7,5 mm?

Posted By Dan D DuBal

I concur with the "get thee a Barlow" (&/or Powermate) advice.

The best 5mm, 4mm, and ~3.3mm eyepieces I've ever used all were "born" from a single 10mm Clave. Sure, I probably have an exceptional older one, but the fact remains -- whether used alone or coupled with my Ultima Barlow &/or my 2.5X Powermate, the Clave never ceases to make me grin.

A very good 10-to-15mm Abbe, Masuyama, Monocentric, or Plossl (or even a UO Konig), when coupled with a very good magnifier, will do an excellent job in the ~3-to-7.5mm range.

Best wishes and luck.
-Dan