Do You Know

[AstroTasmania]

Most optical astronomers will have used a Barlow lens at some stage in their activities, however, how many actually know where the name came from? Judging by the number who spell it as 'barlow' they are probably unaware that it was invented by one Peter Barlow, born in Norwich, England 1776 - 1862. A mathematician and engineer he was a very talented person, his scientific and other contributions earned him a top honour, elected a Fellow of the Royal Society. Over the Years there have been many poor quality Barlow lenses made & sold, which often gives the lens a bad name. Traditionally a two-lens negative achromat, now made as a three-lens apochromat, everyone should have a one.

My Xmas Day trivia.

[joe_smith]

Never knew that mate but do now :yesplease: some smart people out there

[Radar]

Barlows are something I have never really thought about.

What exactly is it that makes a good barlow or a bad one? Why are some barlows longer than others?

If someone were going to buy a good barlow, what advice would you give to them Shev? I have two cheapies, but I am going to start adding to my visual collection in 2007 (including getting a 12 or 14 inch scope if I can afford it).

[AstroTasmania]

Barlow lenses are a two element telenegative lens, which can be used on its own with a camera to give increased magnification. Normal is 2x but can go up to 5x with the TeleVue Powermates. They can be used with an eyepiece to increase its mag by x2, 3x, etc. The best ones are not expensive and an apo (three lens) version is the way to go. Do not buy or use a cheapie, it degrades the image too much. Often sold with dime store scopes to give the 990x magnification!!!! with a resulting bad image.

So with a long or a short 2x Barlow and two EP's, you will have four different magnifications. A good Barlow is cheaper than a good EP. Sometimes you need a 'shorty' barlow just to get the focal point further out of the focuser, as in a PST when you want to use a camera. They come in 1.25" and 2" tube sizes. I use mine a lot.

Clear Skies...

[Radar]

in a PST when you want to use a camera. They come in 1.25" and 2" tube sizes. I use mine a lot.


Interesting, because I could never get mine to come to focus. I didn't think of trying a barlow. Thanks :thumbsupmate: