Posts Made By: jess tauber

I have the opportunity to purchase two identical large front surface mirrors originally manufactured by Perkin Elmer. They are 30 x 40 inches, and curved, about 1 inch thick. Unfortunately they are on the other side of the country and I don't have any way of determining whether they are of any use for an ATM. So far as I can tell they don't appear to be conic sections though I could be wrong- they may be cylindrical- sagitta about 7 inches, so would be a close focus at any rate.

I also don't know what kind of surface smoothness and figural accuracy they have. Not exactly the kind of gamble one wants to plunk down a couple of hundred dollars for, but it they do focus images well that would be a great price. I'm waiting to hear back from the seller to see whether he can follow my instructions to find what kind of focus they do have.

My inquiries to the current Perkin Elmer outfit have gone nowhere- and the seller has no idea how old these are or what their original application was. At least the coatings are relatively new.

Has any of you ever seen one of these things, and can you say what they were used for?? Thanks.

Jess Tauber

OK so I can't remember what its final name is- you know, that wheeled, powered personal transportation system that's supposed to get you around city spaces without having to walk? Its been in the news here and there over the past couple of years. Has onboard computers and maintains its balance as the rider's weight shifts.

Why couldn't we do something like this for a dob mount? Just wheels interacting with the dirt/floor/pavement. Could include progamming to find objects, track, etc. Why not?

Jess Tauber

O when will the insanity end???? I was just reading about the use of shaving mirrors over on CN and their potential use for reflector primaries.

Yeah, I had my idea of utilizing the backs of large security mirrors (some up to 64 inches diameter, which would make a nice aperture if you could figure, polish, and support it, unfortunately they tend to be way too fast (F/2 and under)).

And I've thought of other nontraditional avenues such as meniscus glass, and membranes under over/underpressure (vacuum to you other guys) tension, all of which had been though of by other people.

One of the issues here though is that the material will warp in undesirable ways as it is deformed under tension. Surface area/volume relations and all that. BUT such relations also are affected by temperature.

Soooo, instead of simply fighting such things by creating zero-expansion materials, why not take advantage of such behaviors??? That is, vary the expansion coefficient in a radial (and perhaps also thickness) gradient? A flat sheet of such material will ideally warp in such a way as to produce a usable figure all by itself, and perhaps if done right smooth out in the process, as the temperature changes.

Maybe I need a new supply of mushrooms, but it would be curious if such a thing could be done. Anyone ever heard of gradient expansion materials anywhere?

Jess Tauber

I was playing with a Barlow lens the other day and noticed I could to the 'variable' thing just by playing with the position of the lens in the focuser. Segueue to now and it occurred to me that one might use this effect to make binoculars or a binoscope with objectives that didn't quite match focal length-wise.

Then the only thing to need tweaking might be the relative positioning of the objectives in their tubes forward/backward so eyepieces remain parallel. For refractors this isn't so much of a problem, but for reflectors the focuser positioning versus secondaries creates other issues, such as relative brightness- leading to the second possibility- using objectives of different aperture (with or without masks).

So one could end up with a Frankenstein kluge- the question is whether it will work, regardless of whether it will be pretty?

Thanks.
Jess Tauber

Only posting here because we were talking about similar things just a few days ago.

See ScienceDaily: http://www.sciencedaily.com/releases/2006/10/061002154230.htm

Someday entire telescopes may be made this way.

Jess Tauber

We'll have to see whether France's new Armenian Genocide anti-denial law (very similar to that now law in Germany and Austria re the Jewish Holocaust) will pass. The current French government is wary of upsetting its lucrative business relationships with Turkey.

Apparently the Turks are still too brittle emotionally to swallow this particular pill, even after 90 years. It cuts too close to home re the founding of the current state viz the old Ottoman one? Kinda like George Washington's involvement in the destruction of the Iroquoian tribes before the founding of the good ol' U.S. of A.

And of course the Australian government can't apologize to the native aboriginals, since that might mean lawsuits and compensations and other terrible things. By the way, a recent court decision down under recognized native title to the land under Perth. Stay tuned.

In Turkey of course the 'Armenian Question' was solved by deportation and extinction, but there are the Kurds in the east who still want THEIR own state. The old League of Nations recognized the Kurds as deserving of same, but the then new Turkey didn't feel like relinquishing this particular stretch of land.

In the meantime of course they put a real damper on Kurdish culture, preventing the people from using their language publically, teaching it to their children in school, etc.

Similar suppression was dealt to many different Native American peoples by the U.S. and Canada, either through official channels or indirectly through religious organizations running schools.

All of this must be set at the feet of a particularly virulent strain of insecurity that sees any deviation from self-same likeness as a threat- different races, cultures, languages, religions, political agendas, orientations etc. must be stamped out, extirpated, smothered.

Maybe the world would be much better off if people who believe such nonsense themselves could be corraled somewhere well away of the rest of us- but then anyone contemplating such action would have to join the group in exile itself!

Jess Tauber

As more and more apples tumble from the Republican applecart in anticipation of the upcoming midterms, there is this from the BBC website: 'Bush aides 'mocked evangelicals'' (http://news.bbc.co.uk/2/hi/americas/6054208.stm)

I heard a couple of minutes last night of the interview with David Kuo on the CBS show '60 Minutes' (I think- was just passing through...).

Let the games begin........Who Lost God?

Jess Tauber

In order to be a star, one needs to be above average, special even....I don't think the Sun rates such status, being a yellow dwarf, and thus not even up to sticking up for its putative rights in the HR regime. Nor does it loudly proclaim itself with radiant intensity but slinks along energetically at a slow crawl. Yeah, maybe it shines brighter perhaps than some red dwarfs, but what kinda claim to fame is that, huh? Gimme a blue supergiant any day. Star, schmarr- the Sun on the set is an extra at best.

Jess Tauber

My dead horse again...

Over at CN in their ATM forum I recently posted about deforming from one figure to another (in my case from paraboloid to hyperboloid, but no matter this is just the intro here).

For a long time I've been wondering whether security mirrors (at least relatively flat ones, not domes) could have their mountings removed and be figured/polished to be at least a low power objective. Some of these mirrors are very large, and much cheaper than thicker telescope mirrors- the latter of course being something of a problematic issue. There are 64 inch security mirrors out there for just a few hundred dollars.

Some of these are glass, others are plastic. I'd imagine that although glass might be easier to get a nice polish out of it is just asking for disaster. Plastics have too much play at both the micro and macro level but at least you won't be picking shards out of your toes.

Now we've discussed here in the forums using water jets as a polishing method- could something like this also be used for 'grinding'/figuring of a plastic element? Would a liquid with enough speed/force be able to prevent major gouging of the surface?

There are both thermoplastics (less good) and thermoset plastics (better for stability).

OK, getting past the initial problems (and assuming that proper mounts can be made) what about flexing to paraboloid here? Can it be done with a plastic mirror? Any downsides relative to glass (which of course is stiffer (but Bakelite and similar thermosets (not marmosets)?).

Just feeling about in the dark here....

Jess Tauber

The actual piece is factually '0k' but the title editor is asleep at the switch (http://news.yahoo.com/s/ap/20061101/ap_on_sc/moon_study)

How many times have you seen such stupidity in media rewrites?

OTOH perhaps this is something new we haven't heard about, following hot on the heels of Pluto's planetary demotion?

Jess Tauber