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  1. #1
    Joel_L's Avatar
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    Default Barlow+eyepiece vs eyepiece



    Hi,

    I'm in the process of gathering new eyepieces for my scopes. For my older 8" SCT I have a 10mm and 26mm Plossl eyepieces and a 2X Barlow. I now have added a 1100HD and am gathering some wider field eyepieces. I am happy with the Luminos 23mm that came with the scope, seem to be good for cost. I added a Luminos 15mm and am also looking at some ES 82 and 100 degree eyepieces. Question I have, is there ever a visual advantage to using a Barlow over using a dedicated eyepiece? Meaning, is it ever an advantage to use a 20mm eyepiece plus 2X Barlow over using a 10mm eyepiece? I think adding the 2X Barlow makes the scope slower F10 becomes F20, which leads me to believe a 10mm eyepiece is a better way to go. Am I missing something?

    Thanks

    Joel

  2. #2
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    Default Re: Barlow+eyepiece vs eyepiece

    the main advantage is that you retain the eye relief of the 20mm ep
    for example.
    it also adds more glass into the light train that some people find lessens the view.
    imo,this kind of thing is a personal choice.a little experimentation will help you decide
    whether you prefer the barlow route,or a dedicated ep route.
    hope this helps.
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  3. #3
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    Default Re: Barlow+eyepiece vs eyepiece

    Quote Originally Posted by Joel_L View Post
    I think adding the 2X Barlow makes the scope slower F10 becomes F20, which leads me to believe a 10mm eyepiece is a better way to go.
    "Fast" and "slow" are not really relevant when using an eyepiece. What the barlow really does is give you the same magnification as though the scope had double the focal length. Even if you consider the "effective focal length" to have changed, there is no real effect at the eyepiece except the magnification. (And, as Andy noted, you retain the eye relief of the eyepiece, which is beneficial.)

    Many short focal length eyepieces are actually longer fl eyepieces with barlows built-in. Is there any difference between my 6mm, which is a 12mm with a built-in barlow, and a true 6mm EP? Not really.

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  5. #4
    Joel_L's Avatar
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    Default Re: Barlow+eyepiece vs eyepiece

    Sounds like maintaining eye relief is a good advantage. I will make sure to know what the eye relief is on any of the shorter EPs I'm interested in.

    Thanks

    Joel

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    Default Re: Barlow+eyepiece vs eyepiece

    There is a subtle tradeoff between the longer eye relief of a longer EP with a barlow and a shorter EP with equivalent FoV and magnification.

    The single EP will probably have a very slightly better image, while the longer EP with Barlow will have an easier image to look at due to eye relief.

    If you have an apochromatic refractor, you just might be better off with the single EP approach. If, on the other hand, you have a mass market telescope of ANY kind, it is doubtful that you can see the difference a barlow does to the image quality. That is: In my 6" Astro Physics scope I can see these kinds of subtle image qualities, in my C11 and my 20" DOB I cannot.

    My guess is that 99.44% of you can't either.

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    Default Re: Barlow+eyepiece vs eyepiece

    Quote Originally Posted by MitchAlsup View Post
    There is a subtle tradeoff between the longer eye relief of a longer EP with a barlow and a shorter EP with equivalent FoV and magnification.

    The single EP will probably have a very slightly better image, while the longer EP with Barlow will have an easier image to look at due to eye relief.

    If you have an apochromatic refractor, you just might be better off with the single EP approach. If, on the other hand, you have a mass market telescope of ANY kind, it is doubtful that you can see the difference a barlow does to the image quality. That is: In my 6" Astro Physics scope I can see these kinds of subtle image qualities, in my C11 and my 20" DOB I cannot.

    My guess is that 99.44% of you can't either.
    I would venture to say you are right on that Mitch. Though I tend to agree with you, I just prefer swapping EPs rather than fiddling with a barlow. Logistically, it just suits me better.
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