Magnification

[wookie1965]

Hi I know some Barlow`s can  be unscrewed and then screwed into an eyepiece to change the power. What I want to know is my Tal barlow  the very bottom comes off and will screw into my eyepieces but what would it be X1.5,  x1  or anything in between thanks.

Paul

[M40]

As I understand it, the closer the barlow lens to the eyepiece the less the magnification factor, as such by screwing the barlow to the eyepiece you will reduce its magnification factor. No idea how this will affect focus as I thought that barlows had a focal length determined by the length of the barlow tube.

[Ricochet]

39 minutes ago, wookie1965 said:

would it be X1.5,  x1

Well I would hope that it is not 1x as that would mean it is making no difference at all. As a general rule if you screw the nose piece from a 2x barlow straight to an eyepiece it tends to work out somewhere around 1.5x but it depends on the distance between the lenses. The only way to know for sure is to time how long it takes for a star to drift from one edge to the other, or from centre to edge, with and without the barlow, and then compare the ratio. If your eyepieces have their field lenses in different positions you may have to work it out for each eyepiece. 

[Ricochet]

20 minutes ago, M40 said:

I thought that barlows had a focal length determined by the length of the barlow tube.

The focal length is determined by the lens(es). That is then used to calculate how long the tube needs to be to give the magnification that is desired. 

[Second Time Around]

This is currently being discussed on another topic. 

See https://stargazerslounge.com/topic/402841-baader-hyperion-zoom-and-barlow-fitting-issues/#comment-4317609 and scroll up to the first post.

Edited November 21, 2022 by Second Time Around

[wookie1965]

8 hours ago, Ricochet said:

Well I would hope that it is not 1x as that would mean it is making no difference at all. As a general rule if you screw the nose piece from a 2x barlow straight to an eyepiece it tends to work out somewhere around 1.5x but it depends on the distance between the lenses. The only way to know for sure is to time how long it takes for a star to drift from one edge to the other, or from centre to edge, with and without the barlow, and then compare the ratio. If your eyepieces have their field lenses in different positions you may have to work it out for each eyepiece. 

I was typing too fast and did not proof read it is supposed to be 1.5 and 1.25 thanks for pointing that out.

[Mr Spock]

Easy to do indoors if you have a small scope and a long room - and an extension tube.

Stick a ruler on the wall opposite. Measure the field size first without the Barlow, then with. Then divide one by the other. Simples!