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Posts Made By: jess tauber

July 17, 2005 09:36 PM Forum: Telescope Making

cylindrical mirrors

Posted By jess tauber

Has anyone on this forum had any experience grinding/polishing cylindrical mirrors? I'm looking to make a version of the "mirror-o-matic" for these. Thanks. Jess Tauber phonosema[email protected]

July 29, 2005 07:52 PM Forum: Telescope Making

cylindrical diagonals?

Posted By jess tauber

Hi again. I'm building a binoscope out of two Synta 6" f/8 scopes, and am trying to figure out the best way to bend the light path to severely shorten the overall length. So far I've been hunting around for flats, diagonals, Newtonian secondaries and so on (just got a bunch of inexpensive copier first surface mirrors that probably won't be flat enough).

Anyway, it snapped into my head moments ago as I was reviewing the sketches I have for the design that perhaps one could substitute a cylindrical mirror for two flats perpendicular to each other (causing a 180 light path turn with translation away from the original axis).

The question I have (lacking a ray tracing program) is whether a simple cylindrical unit would suffice here, or would it have to be more like a toroidal mirror, to preserve the trajectories of rays laterally. Just on paper the reflection in the direction of translation away from the original axis looks ok. I have problems with 3D images without having an actual model in front of my face.

Thanks for input.
Jess Tauber
phonosema[email protected]

August 3, 2005 06:58 AM Forum: Telescope Making

In-line finders?

Posted By jess tauber

Ok- I give up on cylindrical finders....

A couple of months back on ebay, I saw an ad for an old ATM-made Newtonian scope that had the finder on the INSIDE of the main tube. I couldn't see from the pictures how it was supposed to be looked into- whether it had its own eyepiece or somehow interacted with the main focuser (I guess with a variant of a flip mirror?).

Obviously it was a narrow aperture finder, since anything else would start getting in the way of the objective mirror. But it got me thinking that perhaps one could mound a finder on the upper side of the secondary. Someone must have thought of this before, and perhaps posted it here? This in-line finder could have an aperture as broad as the narrow axis of the secondary.

If it were just piggybacked it would still need its own eyepiece and focuser, and if it were to feed into the main focuser, then one would still need to be able to flip or turn the secondary. Or I suppose one could use a combination sled and regular in/out focuser with a secondary-piggybacked finder?


Thanks again for your indulgence.
Jess Tauber
[email protected]

August 8, 2005 07:13 PM Forum: Telescope Making

in-line barlow?

Posted By jess tauber

As a continuation of my exploration of what one might be able to do along the main telescope tube axis, I started wondering today whether anyone has ever heard of ATMs placing barlows or focal reducers in between the primary and secondary of a Newtonian system. Something like this might take advantage of the optical shadow already present from the secondary, and at the same time allow much easier use of binoviewers. Yet it would probably require a trap door to put it in when tube is solid. Dunno if any advantage gained in terms of light-loss versus a more traditional mounting at the focuser since intercepting the the full light cone from the primary means wider radius than the secondary- unless its mounted directly on the secondary itself to minimize this effect?

Jess Tauber
phonosema[email protected]

August 24, 2005 03:50 AM Forum: Deep Sky Observing

Galaxy Distribution by Type

Posted By jess tauber

Hi folks. I've got a question regarding the distribution of galaxies by type in the sky. As I was getting myself a basic "up to speed" from my recently purchased set of Burnham's I started noticing that the different types of galaxies aren't spread uniformly in the various constellations- I'm NOT talking here about clumping of galaxies generally, which I'm aware of (such as the Virgo Cluster).

So I started crunching numbers- not only are there some pretty interesting skews in terms of how common different types of galaxies are across the sky, but also there is some real clumping of types as well (for instance ellipticals over here, spiral type 2 over there, and so on), as if something in the local region of formation statistically affected the entire group. Even some different types tend to be found together, at the expense of others.

I'm not aware of ever having read anything like this in any introductory books on cosmology I've read- anyone out there aware of similar findings?

Jess Tauber

August 25, 2005 04:33 PM Forum: Astro Binoculars

Comet King?

Posted By jess tauber

Hi. I just purchased a 20 year old pair of 20x80 Comet King binoculars, and want to know more about them- there is essentially nothing on the WWW, and only a small handful of references here.

Apparently they were made for University Optics- does anyone know for how long they were manufactured? The views are just incredible with these, with crisp pinpoint stars over better than 90% of the field (things get fuzzy only on the very edges between my eyes, and I wonder whether that has more to do with the prisms than with the lenses). I had been thinking of reselling but not now.

Anyone have any good info on this brand? Thanks.

Jess Tauber

September 4, 2005 07:38 PM Forum: Deep Sky Observing

Star cluster patterning?

Posted By jess tauber

Hi. I was observing last night with my old Coulter 10" reflector and sat down to scan the sky between the Double Cluster and the Pleiades. I started wondering whether there was some sort of patterning to the clusters- it almost seemed as if stars were distributed along long strands, like frog eggs- in some radially extended, in others more spirally- the Pleiades seemed especially like the latter.

Is this an optical illusion caused by the mind's insistance on making sense of randomness, or is there really something going on here? Thanks.

Jess Tauber

September 5, 2005 12:29 AM Forum: Telescope Making

panorama camera

Posted By jess tauber

Hi all. I just got a pair of demo 16 inch apparently spherical mirrors, one concave, the other convex, F/ about 2 for the concave. I was thinking maybe I could use the convex one to build some sort of all-sky panoramic film or CCD camera setup, but haven't a clue as to design, the camera needed, etc, or even how to tell if the mirror shape/smoothness is good enough for this application. Any helpful advice? Thanks. Jess Tauber

September 7, 2005 11:40 AM Forum: Telescope Making

gears for porro prisms?

Posted By jess tauber

Hi. For my big binocular project I'm going to have porro prisms next in line before the eyepiece holders, and have wondered whether anyone has heard of using interlocked gear teeth, or other mechanisms, for coordinating their rotation for adjusting interpupillary distance. I don't want to get too complicated, but don't want the ep holders to rotate freely relative to each other either. Thanks.

Jess Tauber

September 9, 2005 01:45 AM Forum: Astro Binoculars

big binos, porro prism rotation

Posted By jess tauber

Hi again. I posted a question about this to the telescope making discussion, but got no takers. Hoping to have better luck here.

Many of the bigger binoculars, especially higher end ones, seem to have fixed barrels, and allow for interocular distance adjustment by rotating their porro prisms. Lots of large military units do the same thing. Anyway, what I want to know is whether anyone knows if the rotations are always completely independent for each eye (which could lead to images not unifying?) or can be linked, say by gear teeth or other mechanism. Thanks.

Jess Tauber