Talk:Cassegrain reflector

Cleanup edits

Cleaned up problems created by wholesale moving of sections from other articles. Deleted Schmidt camera since it is not a cassigrain. Moved other types into organized sub types. Removed "VISAC" since it does not seem to be a distinct sub-type, an external review[1] states that it is basicaly a Richey-Chretien with an added a "field corrector lens" to correct field curvature in wide field applications. Moved it down to Commercially produced Cassegrains and moved extended info to its parent page Vixen (telescopes).Halfblue 04:25, 24 September 2006 (UTC)

Schmidt Cassegrain Field of View

The section on the Schmidt Cassegrain currently begins by stating that it is a 'classic wide field instrument' or words to that effect.

If you click on the link to the main Schmidt Cassegrain article and look at ITS section 'applications' you will see that it says the Schmidt Cassegrain is a narrow field instrument - a direct contradiction.

My own understanding is that the Schmidt Cassegrain has a limited (narrow) field of view i.e. the dedicated article is correct while the general cassegrain article is wrong on this point. I think the author may have got mixed up with the Schmidt Camera (a different instrument) which is classic and does have a wider field of view.

Propose to delete or amend the claim that the Schmidt Cassegrain is a wide field instrument.

To back up what I have said, look at: [2] a review of a very common and typical SCT (Schmidt Cassegrain Telescope). One of the 'cons' noted is 'narrow field of view'. Look at the first bullet point at the bottom of the page here: [3]; look at the last sentence of the first 'catadioptrics' paragraph here: [4]. —Preceding unsigned comment added by 83.67.127.181 (talk) 12:24, 12 September 2007 (UTC)

Mention of Bonaventura Cavalieri

For most academic topics, the first published discussion of the ideas should be mentioned, even if it was not followed up at the time, or intended for a different use.

For example, see the history of the FFT (Fast Fourier Transform). Well after Cooley and Tukey independently derived it in the 1960s, various researchers found it had been previously invented by Gauss in 1805. It was published 50 years later, after his death, in a odd form of Latin, in a discussion of another topic entirely (interpolation of asteroid orbits). Furthermore this approach to orbits turned out to be a dead end, and the paper was never followed up on, or referenced. Yet most histories of the FFT (all since this discovery, as far as I know) acknowledge that Gauss discovered it first. LouScheffer (talk) 14:55, 24 February 2009 (UTC)

Your re-addition was inadvertently rolled up in a revert of vandalism (sorry about that). I did not restore it for the following reason. You state "Yet most histories of the FFT (all since this discovery, as far as I know) acknowledge that Gauss discovered it first". The reference on Bonaventura Cavalieri (Stargazer, the Life and Times of the Telescope, by Fred Watson, p. 134) states "Bonaventura Cavalieri has been seriously underrated by hisotory". Thats the difference, Wikipedia asks that there be significant mainstream scholarly citation of a historical view. The source admits there isn't. Also the facts are miss stated, Bonaventura Cavalieri and Marin Mersenne did not "attempt..(to)..(create)...(Cassegrain reflecting) telescopes", nither attempted to create anything, they simply wrote theories. And Bonaventura Cavalieri did not write about Cassegrain telescope designs at all, he wrote theories about something totally different - burning mirrors. Fountains of Bryn Mawr (talk) 05:36, 26 February 2009 (UTC)

Thanks to google books, you can now see the Lo Specchio Ustorio, overo, Trattato delle settioni coniche on-line and judge for yourself. See figure XXI (near the end) in particular, which shows a parabolic primary and a hyperbolic secondary. That's a Cassegrain configuration, by definition. LouScheffer (talk) 15:45, 26 February 2009 (UTC)

It is Wikipedia policy not to rely on primary source material for the very reason that "judge for yourself" is original research. And reverting still does not address what seems to be a mis-interpretation of reference. Fountains of Bryn Mawr (talk) 16:15, 2 March 2009 (UTC)

If the claim is that author A published idea B in year C, then a primary source is the correct reference. This is true not just for Wikipedia, but almost all academic work as well. A primary reference is the (exceedingly) preferred way to back up such claims (note that in academia, a paper or thesis that does *not* refer to the oldest reference on the topic will be soundly rejected). Furthermore you must reference prior work as soon as you know about it - you cannot (ethically) ignore it just because previous histories did not mention it - you need to look for yourself, and cite it if it's relevant.

Also, the Wikipedia policy states: "Any interpretation of primary source material requires a reliable secondary source for that interpretation. Without a secondary source, a primary source may be used only to make descriptive claims, the accuracy of which is verifiable by a reasonable, educated person without specialist knowledge. " The proposed reference is OK on both grounds independently. First, it's a descriptive claim that a reasonable person could verify - "figure 21 shows a concave primary and a convex secondary". Next, even if the reader might think this amounts to interpretation, a reliable secondary source says the same thing.

Primary sourcing is not the "preferred way to back up such claim(s)" by consensus since Wikipedia is an encyclopedia (see primary source). And we have the further problem that the secondary source that is being used states that Bonaventura Cavalieri is not notable and did not design Cassegrain "telescopes". That is the problem with this version since it makes those statements. I have edited that out but summary Notability is still a question without a reference(s) that states such. Fountains of Bryn Mawr (talk) 18:02, 7 March 2009 (UTC)

External links modified

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