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Posts Made By: Dan D DuBal

July 10, 2002 10:32 PM Forum: Astro Binoculars

Best Bang for the Buck

Posted By Dan D DuBal

I like both the Pentax PCFs and Minolta Activas, among the most readily available brands. My 7x50 Tentos, while far from waterproof, are also great. Zeiss-style body, classic hard leather case, small guide/manual (Russian, German, French, English), and two sets of eyepiece filters (yellow & orange -- no personal opinion yet on their utility). Came off the assembly line in '88, been stored in original packaging since then, arrived perfectly collimated. Good mechanics (albeit not as refined). Optics excellent.

Whopping $50.

I'll probably end up with 12x50 Activas, as well. And maybe Orion's 15x63 Mini-giants. And maybe...
:-)

Cheers and bino fun.
-Dan

July 14, 2002 07:44 PM Forum: Deep Sky Observing

Daytime "star test" question

Posted By Dan D DuBal

Hi Jim.

What scope are you looking to test (focal length & aperture)?

I have Suiter, and I'd be glad to give you some rough (but conservative) guidelines.

I've star-tested using chrome bumbers and other bright solar reflections from distances beyond a mile. I've also star-tested using a precision pinhole at ~30 feet (small refractor). The idea is to image an intensely bright spot at a distance which yields parallel, effectively infinite-distanced light with zero (or minimal) spherical aberration -- an effective airy disc. The smaller the diameter of the reflecting spheroid (or quasi-spheroid), the shorter the minimum working distance needed to do so. Unfortunately, the smaller the image spot, the dimmer the reflection will be. Another unfortunate aspect: the greater the working distance, the greater chance of poor seeing over the intervening distance (hence, no real advantage over true star-testing, other than the artificial star's being stationary). Still, it's do-able.

If nothing else, I can give you a rough idea as to what you'd need to replicate a good-enough artificial star image.

Best wishes.
-Dan

July 17, 2002 07:39 PM Forum: Equipment Talk

Prices on AstroMart

Posted By Dan D DuBal

It's just you.
:-)

Okay, seriously: if you feel stuff is overpriced, that's cool. I don't notice very much, myself. Most items I run across seem appropriately priced for the market (or at least nearly so). And it's that word, "MARKET," which is the key. If there's a ready supply of buyers willing to pay (bad example--) $50 for a once-tried, mis-aligned, discarded-but-mint, prism diagonal, then I have absolutely no problem with folks continuing to feed that market and take the buyers' money. I wouldn't presume to tell one of those buyers, "What're you doing? That prism wasn't worth $50 to you. It was only worth $10 to you."

In some cases, the supply a given item may be zero (or almost zero). If the demand for that item is plentiful, the price will be higher. (If supply is plenty, the price will drop.)

There may very well be just as many UNDER-priced items out there, too. When that happens, how many buyers do you think would come forward and offer pay *more?*

Every deal involves a seller AND a buyer. Why lay blame on the seller?

Best wishes.
-Dan

July 19, 2002 04:09 PM Forum: Eyepieces

Re: Monocentric anyone?

Posted By Dan D DuBal

Yes, it was Jay.

Search on "jay freeman monocentric" will yield a few sources to the same article text.

Here's one link (to SEDS):
http://www.seds.org/billa/psc/or/j17.html

Cheers.
-Dan

July 22, 2002 07:30 PM Forum: Equipment Talk

Can I use 1.25" diagonal in 0.96" scope?

Posted By Dan D DuBal

Hi Colin.

Here's a few questions:

Does the Pentax prism diagonal have a 1.5-inch inlet barrel? (Mine does.)

How much distance (about) between front of prism housing & the juncture of the o.t.a. & drawtube, when scope's focused at infinity (Moon's good). In other words, how much *available* inward travel do you have, when using the prism & your current eyepieces?

Do you have a 1.5-to-1.25-inch adapter?

That's enough ??s for now. I'll let you catch up.

Assuming my prism is like yours, I can confirm the following: I need another inch or so inward, over the Pentax prism, after replacing it with a 1.25-inch mirror diagonal & using typical/standard eyepieces (.96-inch 18mm Kellner to 1.25-inch 18mm Kellner, for example). Maybe ~1.25 inches more, in some cases.

I've never seen an 85 in person. You have a wonderful, rare, achromat. If I ever seen one in the field, I'll pop in & check to see if it's you. (Likewise, if you see a little Pentax 75 EDHF, it might be me).

There's a shot of the 85 (& mount) on the APM website. Is that your layout? Check it out, if you haven't (might need to cut/paste the URL):

http://www.apm-telescopes.de/magazine/images/
PentaxRefraktor.jpg

Best wishes & plenty of available focus travel!
-Dan

July 29, 2002 10:09 PM Forum: Equipment Talk

old Binoculars

Posted By Dan D DuBal

Hi Dave.

Nippon Kogaku was a Nikon "parent" (though N.K. did *not* cease to exist once the "Nikon" brand name was born, 1946). Your pair may pre-date Nikon altogether.

The first Mikron reverse-prism compacts were marketed in 1921. Yes, they are very good. Yes, they are collectible.

I'm not a collector, myself, so I can't offer an informed estimate of their value. If condition is good-to-excellent (clean optics, no delamination, no dents/cracks, etc.), I could see them fetching $80+. However, Nikon/Nippon Kogaku collectors are a *far* better source than I. Their value might be higher -- depending on condition, rarity, features, et.al.

Is there a matching case? If so, that should help value--especially if condition is nice (no mildew, rot, etc.).

Advice: do *NOT* clean them with any type of solvent. Careful cleaning of grime/dirt (if any) is fine, but don't do anything to dissolve/remove the body's existing finish/patina. Ditto for the case, if you have it. In other words, *don't* try to make them look new.

Don't throw anything away, either.

You'll find some historical info at
www.nikonhs.org/history.html

as well as the Nikon Corporation website
www.nikon.co.jp/main/eng/portfolio/history.html

Congrats on finding a nice little piece of Nikon history(actually, a nice piece of binocular/photographic history, in general).

Best wishes.
-Dan

August 15, 2002 07:48 AM Forum: Equipment Talk

.965" eyepieces

Posted By Dan D DuBal

Hi Bob.

Zeiss, Pentax, & Takahashi are most popular among recent (or current, in Tak's case) premium .96 eyepieces. Other (rarer) premium 96ers include JSO, Goto, Nikon, Kowa. Any good example from one of these brands is worth full consideration, in my opinion. Most will have the "orthoscopic" label (whether traditional Abbe or not), but you'll find Kellners & other designs, too. The Pentax XPs, for example, are designed for eyepiece-projection astrophotography, but many folks swear by the 3.8mm XP as a great planetary eyepiece.

Actually, my early '90s Celestron 18mm Kellner is excellent, too.

I'd have absolutely no qualms or hesitation about buying a good example of a .96 orthoscopic or Kellner from any of the above brands, if the price is right.

A bit of trivia, as an aside: the Takahashi 5mm & 7.5mm LE eyepieces utilize negative/amplifying elements in a sub-diameter assembly *within* the 1.25-inch barrel. This assembly is, itself, housed in a .96-inch barrel. If one were so inclined, they could unscrew the 1.25-inch barrel and use either of these LEs in a .96 diagonal or focuser. I've not done this, nor do I suggest it. The sub-diameter barrel is black-anodized alloy and, I'm sure, more prone to scratching/gouging. Removing the 1.25-inch barrel also exposes threads which would be prone to damage, as well.

Best wishes.
-Dan

August 24, 2002 02:31 PM Forum: Equipment Talk

TV Plossls vs. UO Orthos

Posted By Dan D DuBal

Axial fidelity (contrast, sharpness)? No. Not saying UO's are superior -- just that Tele Vues don't beat them.

Field-edge correction in faster scopes? Probably (though not blatantly). I recently had the chance to view the Helix Nebula via Tele Vue 32mm and an f/5 Starmaster. Awesome field, axis to edge.

Best wishes and luck.
-Dan

September 2, 2002 09:33 PM Forum: Equipment Talk

URL needed

Posted By Dan D DuBal

Don't know if you mean Gary Russell (Russell Optics & Machine), or Bill Burnett (Internet Telescope Exchange), but both links can be found on Astromart's "Home" page.

Best wishes.
-Dan

September 3, 2002 07:14 PM Forum: Astro Binoculars

8X binos

Posted By Dan D DuBal

While certainly far from ideal (or even recommended) for stargazing, my 8x32 Canons are capable of showing LOTS of celestial goodies. I can only imagine (with envy) how your Audobons would fare, in comparison.

As for my own 7x50 Tentos, the deal was simply too attractive to ignore. In my case, there were two or three particular attractions:
1) amazingly inexpensive (I paid $50)
2) combination of aperture & wide field of view (7 degs)
3) curiosity (towards Tentos in general)

I'm very impressed with their optical quality. I don't know of a sharper pair of 7-deg. 7x50s available at even three times their cost. If they were 8x50, all the better.

I vividly recall my first view through a pair of 8.5x44 Audobons. Absolutely wonderful to handle, and even nicer to view through. Awesome clarity & color fidelity, and my eyes simply loved them. Very easy/comfy view.

Given their 8-plus-degrees view, I consider the Audobon's off-axis fidelity (beyond 6 degrees) to be relatively good. It's very difficult (& costly) to design & execute a reasonably flat AND very wide field with a sharp edge.

I can quite easily see myself holding a pair of 8.5x44s in the future. Enjoy the heck out of yours.

Best wishes and happy "birding." :-)
-Dan