Talk:Barlow lens

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Modern Barlow lenses?

I have moved this edit to talk because does not cite a source and reads like an advertisment.

Modern Barlow lenses are usually good in quality. With the growing popularity of premium short focus apochromatic refractors, higher power barlows lens like 5x Tele Vue Powermate was introduced to the market to allow high power observation. These high power Barlows lenses contain more lens elements than traditional Barlows lens to minimize pupil abberation.

Please clean up if you are going to re-add it. thanks Fountains of Bryn Mawr 06:35, 2 February 2007 (UTC)[reply]

Recent removal

I took out the following passage:

Barlow lenses have an unfortunate reputation in some quarters due to poor results given by the Barlows included with some inexpensive telescopes. These results, however, are perhaps better attributed to poor optics and shaky mounts permitting less practical magnification in these telescopes than to an inherent failing of Barlow lenses.

While the entire article is uncited, this bothered me especially, since all the weasel-wording makes it sound like someone's OR. intooblv (talk) 20:56, 23 December 2007 (UTC)[reply]

Similarities with Teleconverter

Shoudn't the similarities with a teleconverter be more emphasized in this article, and perhaps in the Teleconverter article also? We are speaking of the same thing basically, with different names. Photographic teleconverters also exist in different prices and designs, some better than others. They modify the apparent focal lenght of the main lens, just like a Barlow. There seems to be a gap between astronomical optics and photographic optics community, with different names being used for similar things... we should try to bridge that gap, since this is an enciclopedia. Rnbc (talk) 00:03, 11 August 2008 (UTC)[reply]

I do not understand the second paragraph - the one beginning "In astronomical use". What does "before" in "before the eyepiece" mean? Between the eyepiece and the eye, or between the objective lens and the eyepiece? The diagram shows a beam passing first a converging, then a diverging lens. The latter causes the beam to converge further from the former than it otherwise would, incresing its effective focal length. The text says that a diverging lens effectively decreases the focal length of another lens. How could it?

78.147.143.15 (talk) 16:31, 25 February 2010 (UTC)[reply]

The second paragraph of the article (beginning “In its astronomical use”) does not make sense. What does “before” in “before an eyepiece” mean? Does it mean in front of – i.e. between the eyepiece and the eye or does it mean that light hits the Barlow lens before it hits the eyepiece so the Barlow lens is between the objective and the eyepiece? The text claims that a diverging lens decreases the focal length of a converging lens. This is absurd. The absurdity is shown by the diagram which demonstrates how a diverging lens increases the focal length of a lens by moving the outgoing rays from the position shown in red to that shown in green. The text further claims that the diverging lens increases magnification but the diagram shows that it decreases it; the angle between the green rays is less than that between the red rays.

Bukovets (talk) 16:14, 26 February 2010 (UTC)[reply]