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  1. #1
    loki41872's Avatar
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    Default Tell me about barlow use!



    Looking at different barlows, and have some questions on different ways they can be used.

    I'm looking at the 2" ED barlows that are out there, and see that most come with a removable lense cell. I would like to know the different effects that can be achieved by using this feature.

    Standard use, of course, is to insert the barlow into the diagonal and then insert the eyepiece. I know how this works, but what would be the effect of using 1.25 eyepieces with a 2" barlow? Will this increase the FOV?

    Now, how about switching up the configuration.

    Removing the lense element from the barlow and screwing it directly to the diagonal back, what is the effect? I have read it will increase the focal ratio of the scope itself.

    Inserting the barlow into the focuser tube and then inserting the diagonal into the barlow.. what would this do?
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  2. #2
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    A barlow in effect doubles your eps So if you have say a 40mm ep and you insert a barlow it becomes like a 20mm ep.
    Experiment with this link here...Telescope Comparison

    Click on the barlow to give you what I cant explain with my words...
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  3. #3
    loki41872's Avatar
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    Quote Originally Posted by Dublin sky watch View Post
    A barlow in effect doubles your eps So if you have say a 40mm ep and you insert a barlow it becomes like a 20mm ep.
    Experiment with this link here...Telescope Comparison

    Click on the barlow to give you what I cant explain with my words...
    That part I know. I'm wanting to know about using the barlow in the scope, instead of the way it was intended, such as putting the barlow into the focuser tube, and then inserting the diagonal into the barlow. Some sites say that this will increase the focal length of the scope instead of doubling the eyepiece power.
    Last edited by loki41872; 01-02-2011 at 07:52 PM.
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  4. #4
    WWPierre's Avatar
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    Default

    I think Loki was looking for more in-depth info on the effects of using barlows in different ways than the usual, Declan. I have a 2" ep with a removable 1.5 barlow, and will try some experiments tonight.
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    Default

    I believe if you screw in the element directly into the diagonal it becomes 3x.

    Not sure -- Pierre will report tomorrow. Got to be honest and say I have a 2x and a 3x barlow but rarely use them anymore since I also have a wide range of eyepieces.
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  6. #6
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    Default

    Quote Originally Posted by Joe Lalumia View Post
    I believe if you screw in the element directly into the diagonal it becomes 3x.

    Not sure -- Pierre will report tomorrow. Got to be honest and say I have a 2x and a 3x barlow but rarely use them anymore since I also have a wide range of eyepieces.
    I only have a modest collection of eyepieces. I am wondering on how using the barlow differently could give a wide range of power with only a few eyepieces.

    From what I've found out it seems that

    Barlow element screwed into eyepiece gives 1.5x
    Eyepiece in the barlow gives 2x
    Barlow element screwed into diagonal gives 3x
    Entire balow ahead of the diagonal gives 3.5x

    Of course, I WANT more eyepieces! Who doesn't? But I was looking into as many different ways of using the ones I have now, by only buying one piece of equipment.

    I can't find the article I was reading about putting the entire barlow in front of the diagonal, but it claimed that that would change the focal length of the scope itself, like a bird-jones reflector.
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  8. #7
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    Default

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  9. #8
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    The instructions from my 2x Orion Shorty-Plus 3-Element barlow says the same thing - a 2x if placed before the diagonal becomes a 3x.

    Alternatively, a barlow lens can be placed before the diagonal, that is,
    between the telescope and the diagonal . In this case the barlow’s
    magnification factor is increased by about 50%. So a 2x barlow
    placed between the telescope and the diagonal provides about a 3x magnification
    boost

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    My 2" 1.5 "barlow" is just another element that screws onto the bottom of a 30mm EP, making it a 20mm. I'll try screwing it to the front of the diagonal tonight and see how it works.
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    Quote Originally Posted by WWPierre View Post
    My 2" 1.5 "barlow" is just another element that screws onto the bottom of a 30mm EP, making it a 20mm. I'll try screwing it to the front of the diagonal tonight and see how it works.
    Is that the thing from Owl Astronomy? The 20mm Ulta-wide EP with removable bottom element?
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