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  1. #1
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    Default Eyepiece or Eyepiece + Barlow?



    Dumb beginner's question. Given the choice of a 12mm eyepiece or a 24mm eyepiece with a 2x Barlow, is it assumed that the Barlow combination would be better as it doesn't narrow the "viewing circle" (FOV?) as much as or if at all than the 12mm eyepiece alone?

    The above assumes similar quality throughout the 3 pieces.
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    Quote Originally Posted by kingmeow View Post
    Dumb beginner's question. Given the choice of a 12mm eyepiece or a 24mm eyepiece with a 2x Barlow, is it assumed that the Barlow combination would be better as it doesn't narrow the "viewing circle" (FOV?) as much as or if at all than the 12mm eyepiece alone?

    The above assumes similar quality throughout the 3 pieces.
    No, the Barlow would still narrow the FOV. The penalty with the Barlow is a (slight, if quality) loss of light, and the benefit is that you will get the eye relief of the 24mm.
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  4. #3
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    Ah, thank you Dave! Yes, ER of course! That's what I was looking for as I'm an eyeglass wearer.
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    Quote Originally Posted by DaveW View Post
    The penalty with the Barlow is a (slight, if quality) loss of light
    Yep, and depending on the quality of the barlow possible image degradation as well. I try to avoid using my barlow as much as possible.

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    Quote Originally Posted by DaveW View Post
    No, the Barlow would still narrow the FOV.
    Kingmeow's original post is correct, the apparent field of view (AFOV) does not change or "narrow" the AFOV. What narrows down is the true field of view (TFOV) because the magnifcation increases. Use of barlows is a mixed bag, some prefer using it, others don't because it adds an extra glass on the optical train which may result in a less sharper image than when using an un-barlowed eyepiece (EP). Consider also the ergonomics of using one - on a big EP it might be unwieldy using a barlow because the setup can become really big.


    3x barlow on a Hyperion zoom in a WO 66mm refractor

    Best,

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    Last edited by ibase; 09-15-2010 at 12:18 AM.

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    Awesome photo Hernando! So which one is the scope and which is the eyepiece? LOL!

    Looks like a Barlow in my future (Celestron Ultima 2x).
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    Hahaha Thanks; funny you asked that question, others who've seen the setup wonder the same thing too.

    Good choice on the Ultima 2x barlow, can't go wrong with it, very good reviews/feedback on that one.

    Best,

    Hernando

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    Quote Originally Posted by ibase View Post
    Kingmeow's original post is correct, the apparent field of view (AFOV) does not change or "narrow" the AFOV. What narrows down is the true field of view (TFOV) because the magnifcation increases. Use of barlows is a mixed bag, some prefer using it, others don't because it adds an extra glass on the optical train which may result in a less sharper image than when using an un-barlowed eyepiece (EP). Consider also the ergonomics of using one - on a big EP it might be unwieldy using a barlow because the setup can become really big.

    Best,

    Hernando
    It depends whether you interpret FOV to mean the actual field of view, or the apparent field of view. I suppose I should have been more clear. Generally when someone says FOV I assume they mean the true field of view, not the width of the apparent field of view.

    Personally, I use my barlow all the time, as I find that if I really want a magnified view of a bright object like the moon it's easier on the eye and back to use a 15mm with a barlow than to put my eye 4.5mm from my 6mm Plossl. For fainter objects it's questionable, but then I don't really have the aperture to view faint objects at high mag anyway.
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