Marmot Posted April 29, 2021 Share Posted April 29, 2021 Hi i am a novice at this game and this is my first post (apart from saying hello) and it will no doubt be the first of a number of questions I have: Whilst looking at Barlow lenses I have seen adverts for Barlow Lenses, Focal Extenders and Tele Extenders! They all seem to be going the same thing (increasing magnification), but I am a little confused as to weather there is actually a difference between them. The question therefore is weather there is a difference, what the difference is and weather one is therefore better than the other? My interest is purely visual observing and not AP (in case that is relevant). Thanks to anyone who can shed light on this matter. Martin Quote Link to comment Share on other sites More sharing options...
Nightspore Posted April 29, 2021 Share Posted April 29, 2021 (edited) Barlow lenses were invented by Peter Barlow and are a form of diverging (negative) doublet lens that effectively increases the focal length of the telescope it is used in. Some modern Barlows have three or more elements. https://en.wikipedia.org/wiki/Barlow_lens AFAIK tele extender lenses use at least four elements and work on a slightly different principle, even though the end result is basically the same. https://www.televue.com/engine/TV3b_page.asp?id=53&Tab=_back As I see it the primary advantage of the extender/amplifier over the traditional Barlow is that as the light rays are more parallel there is no change to the eye relief of the original eyepiece. A normal Barlow can increase eye relief, which may not be preferred. Edited April 29, 2021 by Nightspore Quote Link to comment Share on other sites More sharing options...
Marmot Posted April 29, 2021 Author Share Posted April 29, 2021 Thanks Nightspore. You replied to some of my questions on The Shed and here you are doing it again in The Yard!🙂 thanks Martin Quote Link to comment Share on other sites More sharing options...
Nightspore Posted April 29, 2021 Share Posted April 29, 2021 You're welcome. Old habits die hard. lol Quote Link to comment Share on other sites More sharing options...
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