Talk:Telescope

I have remove the following statement, which I think correspond not to spherical aberration but field curvature. -- looxix 19:33 Apr 21, 2003 (UTC)

Some schmidt cassegrains have intentional spherical aberration, and compensate with a film-holder that stretches the film into a mild spherical shape.

The Telescope mountings para is largely incomplete lacks equatorial and meridian mount. Ericd 01:47 Apr 22, 2003 (UTC)

I am not conviced by :

"The phenomenon of optical diffraction sets a limit to the resolution and image quality that any telescope can achieve. We still do not know when this limit will be reached, but most astronomers believe we will reach it sooner or later."

IMO diffraction occurs with a small apertures and research telescope have large apertures.

But, I'm not a specialist. Ericd 17:56, 2 Oct 2003 (UTC)

You can read about the influence of diffraction on resolution limits at the [link provided at the bottom of the page, but I'll clarify in the article. Nixdorf 23:08, 3 Oct 2003 (UTC)

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Would anyone be interested helping with a Wikipedia:WikiProject Telescopes and/or Wikipedia:WikiProject Space Telescopes? Should a telescopes template include space telescopes? It/they could be modeled after the following articles:

• Wikipedia:WikiProject Astronomical Objects
• Hubble Space Telescope
• Spitzer Space Telescope
• Arecibo Radio Telescope

--zandperl 15:23, 16 Feb 2004 (UTC)

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The article doesn't seem to mention photography through telescopes. I'm not sure if it should, but I was looking for that. --blades 10:05, 30 May 2004 (UTC)

Synthetic aperture vs adaptive optics

It is my understanding that synthetic aperture refers to a technology for radio telescopes, while adaptive optics is an entirely different technology used for optical telescopes. But this article seems to use synthetic aperture for both. (It might even be using the term to cover interferometry, in one instance). Am I mistaken - does synthetic aperture apply to optical telescopes ? -Willmcw 06:47, 11 Dec 2004 (UTC)

Umm, I am not an expert, but yes, both techniques are applicable to optical telescopes. Both are important and should be described. Briefly:

Adaptive optics refers to a set of techniques for distoring the received wavefront to correct for measured distortions along the optical path (e.g. effects of the atmosphere). They are being used with great success in many new telescopes.

Synthetic aperture refers to a set of techniques for combining information from several telescopes at one time or the same telescope at different places, for instance, to approach the resolution of a much larger physical telescope (one with a larger aperture). Synthetic aperture techniques have been employed for many years, with great success, in so called "sideways looking" radar and sonar systems, for instance. Optical and radio telescope arrays are synthetic aperture techniques. --AJim 04:58, 20 Dec 2004 (UTC)

Just linking the existing entry on Aperture Synthesis (AS) to the this discussion. AS as used in the Very Large Array allows the VLA to operate in at least 4 different modes (1) giving astromers varying magnification capabilities. A similar optical configuration is demonstrated in the Very Large Telescope. This last case also uses Adaptive optics to cancel out atmospheric distortion to near exoatmospheric levels and aperture synthesis of up to four stand-alone telescopes.

A "third" technology being implemented in the James Webb Space Telescope boasts some interesting benefits. Active Optics allows the development of super-lightweight mirrors which can be collected together to perform as one larger unit. The JWST primary mirror is a system of eighteeen smaller mirrors (1.3m) which are phase-synchronized to produce the capabilty of a single larger unit. Just to quantify the gain, the JWST as reported by NASA, will be equipped with a primary mirror that has a diameter of 6.5m versus Hubble's Primary Mirror (2.5m)(2), yet 1/10th the weight. In fact, "if Hubble's [primary] mirror were scaled to match [that of the JWST] it would be unlaunchable. There isn't a launch system capable of supporting a [payload of the required size and in weight]"(2).

COMPARING THE THREE

Active Optics systems differ from both synthetic apperature and adaptive optics. As noted above, "adaptive optics" are used to correct some depreciation of information collected by the mirror. "Synthetic Aperature" systems rely on comparing the collected information derived from two (or more) spatialy distant observation points (OP); these calculations are greatly affected by the know position and inter-relationships of the OPs. SAs also allow obersavation systems to retrieve information from obscured points of interest (e.g., clouds covering the Martian surface) by way of differential measurement. "Active" optics allow a system of mirrors to integrate into one larger unit and provide faster correction capabilities.

(1) - 'NRAO Very Large Array: Configurations'

(2) - 'NASA's James Webb Space Telescope Information Website'.

--'User:CSR' 15:12 UTC, 051202

Largest Telescope in 19th Century

I'm not sure if it's true, but I've often heard that the Ross Castle Telescope in Birr, Ireland was the largest telescope for over 50 years (which 50 years is disputed :)). This information is on the Birr page in Wikipedia (http://en.wikipedia.org/wiki/Birr). Perhaps it would be good to explain how the 91-cm refracting telescope at Lick Observatory be bigger than the 72-inch reflector at Birr?

Good catch. It may take some careful research and writing, but the difference may be between whether the telescopes are usable for science. There have been several large telescopes that were not usable. I understand that the Birr telescope was marginally useful, but someone else may have better information.-Willmcw 19:41, 3 Jan 2005 (UTC)

Suggested changes

If no-one has any objections, I will copy the section "Famous optical telescopes" to the optical telescopes page, and alter the section on this one so it lists "Famous telescopes" (including non-optical telescopes e.g. Chandra, the VLA and ALMA). This would make the section better matched to the article. Rnt20 11:52, 4 Jun 2005 (UTC)

Only astronomical?

The opening sentence -- 'A telescope is an astronomical tool' -- is incorrect. Astronomical telescopes are, it seems, the most interesting in terms of large-scale progress, but historically, telescope uses features more strongly in military and navigational contexts (then, as now, that's where the best funding tended to come from). The opening paragraph should therefore not define telescopes as purely for astronomy, but instead indicate that this article is primarily about astronomical telescopes - and perhaps it would be worth indicating where to find articles about other kinds of telescopes (such as hunters' binoculars, photographers' telephoto lenses, opera glasses).

--69.177.103.38 22:51, 26 December 2005 (UTC)

This can be done. --Excaliburo 15:19, 27 December 2005 (UTC)

Euro50

I just read a Swedish newspaper article on the Euro50 telescope project, planned by a multinational consortium (Finland, Ireland, Spain, Sweden and the UK). It has no WP article yet as far as I can see, but there is a website devoted to it here, in case anyone is interested in writing something about it. up◦land 10:55, 12 March 2006 (UTC)

Largest Optical Telescope

Aloha,

I would note that SALT (South African Large Telescope) is, I believe, a fixed-altitude design like the Hobby-Eberly telescope in west Texas. They're based on the Keck design, but with no up-down tilt, using a movable secondary mirror or prime focus instead, and I have heard that this limits their use to spectroscopy, as opposed to actual photometric imaging. Also, if SALT is identical the HET design, it may use an "oval" mirror, 11m by 9m, as opposed to Keck's "round" 10m diameter one. (I put the words in quotes because all are made of hexagonal segments.) Since HET is only 9m across in one direction, it has been considered "smaller" than Keck.

GTC in the Canaries is has a full altazimuth mount, I think, and at 10.4m would definitely surpass the Kecks size-wise. Bold text

Leonard Digges

His invention of his telescope (1570s according to article) doesn't match his age, he died more than 10 years before in 1559

Copyright Violation in Types

Last night I tagged the entire types section as a copyright violation. There were two brackets on the end, and when I Googled the text, it came back (word for word) to a Galileo website. Nwwaew 11:22, 19 September 2006 (UTC)