Talk:Refracting telescope

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convex?
"Convex lenses are lenses that are thicker on the outside compared to the middle"...huh? I think it should be the other way around, such as: Convex lenses are lenses that are thicker in the middle compared to the outside.

The terms "convex" and "concave" strictly apply to surfaces. In the Galilean telescope the objective is best described as a "bi-convex" lens - or simply "converging". The eye piece lens in this telescope was "plano-concave" - or simply "diverging" and the concave surface was outside - i.e. on the eye side. —Preceding unsigned comment added by Cannocchiale (talk • contribs) 23:25, 4 June 2009 (UTC)

Refraction
The article referred to Galileo's understanding of refraction. The law of refraction did not become widely known in Europe until 1637. Trial and error were used by all parties, until then. —Preceding unsigned comment added by 87.194.4.21 (talk) 13:22, 25 November 2008 (UTC)

Additions
I have rm'ed these additions to the article and removed some of it to below on this this talk page. Much useful description was (accidently?) removed. Allot of this needs verification (WP:V) before being re-added and some of it sounds like it is opinion and needs to be referenced as such (WP:NPOV). Much more of the other material looks like id should be added to their more relevant articles such as Achromatic telescope and Achromatic lens for example. Again it also needs reference. Fountains of Bryn Mawr (talk) 22:29, 1 April 2009 (UTC)

Dutch telescopes had also appeared in Rome and Naples before Galileo built his first. Galileo had initially heard about the telescope from Fra Paolo Sarpi, his Venetian anti-clerical friend who was in correspondence with an ex-student of Galileo, a French nobleman in Paris, Jacques Badovere. Sarpi was also involved in astronomical work, and he remained a close friend and correspondent of Galileo, despite being attacked by the Varican for his pro-Protestant views -- which played a large part in the Church's later attacks on Galileo.

In making his telescope, Galileo, almost certainly had a rough sketch of the Dutch instrument, but he also had a better knowledge of theoretical optics having spent time during the previous few years involved in optical research, so he was able to build a better instrument. Lens grinders had practical experience, but no theoretical understanding of complex optics.

Recent claims that he personally learned to grind lenses and so made a superior instrument seem to have no foundation. He had direct access to Venetian glass craftsmen, who had 200 years of glass-making and lens-grinding experience and were clearly the best in the world. His lenses have been tested in recent times and shown to be only marginally inferior to those that could be ground today (although they had no correction for colour fringe).

Advantages and applications
Some discussion of the advantages of refracting vs. reflecting telescopes seems warranted, and it also seems like it would be helpful to have a section on applications. For example, for advantages, refracting telescopes don't have occlusions, and therefore don't produce diffraction artifacts. They are also simpler. For applications, they form functional units in a large number of optical systems, such as most microscopes, both for simplicity and because of the diffraction artifact issue. And of course they're sometimes used for entry-level star-gazing telescopes. Ycajal (talk) 18:45, 24 June 2018 (UTC)


 * Refractors are used in much more than "entry-level telescopes." Astrophotography routinely uses refractors (and sometimes rather small 80-mm apochromatics) to create superb images. Refractors are lighter and more portable than reflectors. They also rarely (indeed, almost never) require collimation. So they are more robust than reflectors and create significantly better images in similar objective sizes. Reflectors are less expensive to make and have little chromatic aberration. Sagging in the glass of refractors becomes a problem in giant 40" or larger lenses. (See the article on the Yerkes refractor). 148.170.196.55 (talk) 22:39, 15 December 2022 (UTC)

Use of exotic glasses in refracting telescopes
High quliaty astronomical telescopes often use specialized glasses, often based on Lanthanium or Ytrium. They are also used in other very high performance optical systems, like some telephoto lenses, photolithography equipment in semiconductor industry and microscopy. It might be making a note of that? 2A02:168:2000:5B:BFF5:CA65:7F9E:4032 (talk) 23:13, 11 August 2020 (UTC)

Keplerian telescope information doesn't make any sense
" but to overcome aberrations the simple objective lens needs to have a very high f-ratio (Johannes Hevelius built one with a 46-metre (150 ft) focal length, and even longer tubeless "aerial telescopes" were constructed)."

I am skeptical about this statement. f-ratio (aka f-number) isn't sufficient to overcome all aberrations. The statement in parentheses mentions a telescope with a large focal length, which is not the same as the f-number, so this reference doesn't make any sense. Sedlaon (talk) 11:30, 20 January 2023 (UTC)
 * It actually doesn't say it overcame all aberrations but that it overcame aberration. Its further explained at Aerial telescope (the uncorrected chromatic aberration fell within the large diffraction pattern at focus) with a source further explaining "chromatic aberration... diminished when the ratio between the focal length and the diameter of the objective was increased". It could be further explained that these are very small diameter objectives and therefor very high f-ratios. There may even be a source on what f-ratio they were using (or had to use). Fountains of Bryn Mawr (talk) 15:10, 21 January 2023 (UTC)