Talk:Refracting telescope

message: "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)
thread_title:  convex? 

message: 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)
thread_title:  Refraction 

message: 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)
thread_title: Additions

message: 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)
replies: text: 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)
thread_title:  Advantages and applications 

message: 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)
thread_title:  Use of exotic glasses in refracting telescopes 

message: " 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)
replies: text: 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)
thread_title:  Keplerian telescope information doesn't make any sense