How does Barlow lens work ?

[Shivam_yadav]

Hey,
 

- I want to know how is barlow lens useful ! How much it helps to magnify ? 

Please share some photos clicked by you with and without barlow lens ! 
 

- How to chose a barlow lens ? 

Thanks 

Shivam

[AlexB67]

Hey,

- I want to know how is barlow lens useful ! How much it helps to magnify ? 

Please share some photos clicked by you with and without barlow lens ! 

- How to chose a barlow lens ? 

Thanks 

Shivam

Hi Shivam,

You may find this video useful as a decent introduction to barlows.

In a nutshell it alters the focal length of the telescope, so a 2x will double the focal length of the telescope, and therefore provide double the magnification and approximately half the field of view (FOV) or even a bit less of that FOV depending on the design. The video show how they fit into the scope and can be used.

Hope that helps a bit

[Charic]

Shivam......Usefull because it reduces the focal length of the lens in use. A 12mm lens becomes a 6mm lens. If you have 3 lenses say.......8mm 24mm and 32mm then use a 2xBarlow, you now have 6 lenses as the three you already have will be reduced by the barlow, so the 8mm 24mm & 32mm will give the end result of 4mm, 8mm, 12mm,16mm 24mm & 32mm. Thats three extra lenses for the price of a Barlow. Magnification is obtained by dividing the Focal length of the telescope by the Focal length of the eyepiece in use. If you buy a 2XBarlow, the Barlow doubles the Focal length of the Telescope ( changes Focal ratio too, FL/Do) if you buy a 3X barlow it triples the focal length. If the Original focal length of an 8" Mirror is 1200mm and using an 8mm eyepiece you will have a magnification of 150x. If you use a 2xBarlow, the telescope now becomes 2400mm divided by the 8mm = 300X magnification. Increased magnification is not always the best option, as your field of view decreases, and gets darker at those higher levels. The more you pay for the barlow, the better it gets. Choose a Barlow that has  3 or more lenses , ensure that the lenses are glass, NOT PLASTIC!
AlexB67.......I dont see the video Link?
 

[AlexB67]

Shows fine for me as an embedded video in explorer, browser issue or settings ??  , anyway here is the link  http://www.youtube.com/watch?v=ENCbtFpdKJ0

[hobsey]

That is a very informative video as I haven't got one yet.

The only thing he didn't cover is, whats the difference with long and shorty barlows? which one would be suited for a specific scope.

I'm guessing, the longer ones for more focal movement such as a newtonian and a shorty for a a MAK with a 45 or 90 degree diagonal?

[hobsey]

Shows fine for me as an embedded video in explorer, browser issue or settings ??  , anyway here is the link  http://www.youtube.com/watch?v=ENCbtFpdKJ0

Link is working fine in Chrome.

[Charic]

Shows fine for me as an embedded video in explorer, browser issue or settings ??  , anyway here is the link  http://www.youtube.com/watch?v=ENCbtFpdKJ0

Cheers.............Done my checks, filtering and all-sorts off, but still no show in IE9. Double checked in Mozilla and all`s well...........

[stargazerslivingroom]

Cheers.............Done my checks, filtering and all-sorts off, but still no show in IE9. Double checked in Mozilla and all`s well...........

This rings a bell from before I switched browser....Try running in compatibility mode.

HTH

Steve

[Peter Drew]

At the risk of being a pedant, in the interests of accuracy, a 2X Barlow doesn't double the focal length of a telescope or halve the focal length of the eyepiece. What it does do is double the EFFECTIVE focal length of the telescope by altering the converging light cone of the telescope to that which would be presented to the eyepiece by an objective or primary mirror twice the focal length of the original, the eyepiece as a result, doubles the magnification.    

[AlexB67]

Right you are, pendant or not.

[Shivam_yadav]

Hi Shivam,

You may find this video useful as a decent introduction to barlows.

In a nutshell it alters the focal length of the telescope, so a 2x will double the focal length of the telescope, and therefore provide double the magnification and approximately half the field of view (FOV) or even a bit less of that FOV depending on the design. The video show how they fit into the scope and can be used.

Hope that helps a bit

Thank you Alex ! 

[Shivam_yadav]

Shivam......Usefull because it reduces the focal length of the lens in use. A 12mm lens becomes a 6mm lens. If you have 3 lenses say.......8mm 24mm and 32mm then use a 2xBarlow, you now have 6 lenses as the three you already have will be reduced by the barlow, so the 8mm 24mm & 32mm will give the end result of 4mm, 8mm, 12mm,16mm 24mm & 32mm. Thats three extra lenses for the price of a Barlow. Magnification is obtained by dividing the Focal length of the telescope by the Focal length of the eyepiece in use. If you buy a 2XBarlow, the Barlow doubles the Focal length of the Telescope ( changes Focal ratio too, FL/Do) if you buy a 3X barlow it triples the focal length. If the Original focal length of an 8" Mirror is 1200mm and using an 8mm eyepiece you will have a magnification of 150x. If you use a 2xBarlow, the telescope now becomes 2400mm divided by the 8mm = 300X magnification. Increased magnification is not always the best option, as your field of view decreases, and gets darker at those higher levels. The more you pay for the barlow, the better it gets. Choose a Barlow that has  3 or more lenses , ensure that the lenses are glass, NOT PLASTIC!

AlexB67.......I dont see the video Link?

Thanks Charic ! 

[Shivam_yadav]

From where would I get cheap but quality Barlow Lens ? 

[Charic]

Shivam_yadav

 you could check this site out, their selling at 1776.89 rupee at http://www.spacearcade.in/barlow-lens.html from their main web site http://www.spacearcade.in/index.html

[Charic]

Shivam_yadav......... celestron, ultima, Orion, tele Vue, meade, revelation all make Barlow lenses. Just be sure to get the best you can afford, several lenses in the Barlow are better (3+) a metal body maybe a consideration. So much to choose from.

[Shivam_yadav]

Shivam_yadav

 you could check this site out, their selling at 1776.89 rupee at http://www.spacearcade.in/barlow-lens.html from their main web site http://www.spacearcade.in/index.html

Thank You Charic ! I found a dealer near my house !   It was so difficult to find one but know I have found one on the link you gave ! 

[Shivam_yadav]

What to go for an eyepiece or a barlow lens ? 

Because I have read barlow lens of higher magnification lower the brightness ?  
And don't know much about eyepiece whether it too does so or not ! 

[Charic]

Shivam_yadav..... I would change the 10mm lens you have for a better quality lens. Check that website, they do a standard Plossl 10mm for about 2798.00INR, excluding tax, Thats about £28 in my money, so fairly cheap, but also check other websites if your able to. The barlow is something that you may want to buy at a later stage. Buying a Barlow now, would not really do any justice to the basic lenses supplied with the scope you have.  Here`s some interesting reading about lenses. http://www.swindonstargazers.com/beginners/eyepieces.htm. 

As for the brightness, it  will be reduced slightly, because at higher magnification, the view is tighter so basicaly, less light gets through ( in its most simplistic terms, before I`m corrected ?  trying to keep it simple here).  So if you use a higher magnification lens (below 10mm) or a Barlow, there will be a slight reduction. take care.

[Charic]

........ i forgot to add ( I  cant edit my own texts just yet)  the reduction in brightness  you mention is not such a bad thing? You may find that you get a better contrast between certain objects against the darker sky.