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  1. #1
    WalterK's Avatar
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    Default Eye piece advice



    I am new, and I have a 20,10,and 4mm eye piece. I am looking for something that shows a wider FOV for targeting and good optics on a budget.

    I heard 32mm is good to get but I also seen larger. Would 32 be the standard?
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  2. #2
    KathyNS's Avatar
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    Default

    The eyepiece range that is suitable for your scope depends on what scope you have.

    If your 4mm is truly usable (often high-mag eyepieces are thrown into kits to give impressive magnification numbers rather than to give usable views) then 32mm is likely too wide. On the other hand, if the 4mm is too much for your scope, then the 32mm might be just right.

    If you can post the specs for your scope (any two of: aperture, focal length, focal ratio), we could give you a more definite answer.

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  4. #3
    WalterK's Avatar
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    Default

    Yup, I am sorry it's a zhummel 5mm extended eye relief I bought extra for 50.00 I believe. It works great. Helps a great deal with Jupiter.

    Anyway: 114mm, 1000mm, and f/9. Highest issuable magnification is 269x.
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    Default

    Quote Originally Posted by WalterK View Post
    Yup, I am sorry it's a zhummel 5mm extended eye relief I bought extra for 50.00 I believe. It works great. Helps a great deal with Jupiter.

    Anyway: 114mm, 1000mm, and f/9. Highest issuable magnification is 269x.
    f/9 means that your normal usable eyepiece range is 9mm to 63mm. Don't be surprised if the 5mm is sometimes less clear than you'd like - that would be normal in that scope. A 32mm would be a fine wide-angle eyepiece for that scope.

    Never believe a manufacturer's claim of "highest usable magnification". They all lie. Your highest usable magnification will be 114x in average conditions, and 228x in excellent conditions.

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  7. #5
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    Default

    So let me see if I got this straight for my setup:

    5mm=200x
    10mm=100x
    20mm=50x
    32mm=31.25x - is this usable?

    I want to get a Barlow and deciding between a 3x and a 2x.
    The the 3x in same order would be
    600x
    300x
    150x
    93.75 x

    And 2x would be
    400x
    200x
    100x
    62.5x

    What would be more reasonable? The bigger numbers look better but I am assuming won't work with my scope. 0r should I get a variable Barlow?

    Side question: Would f/6 or larger include f/9 or would it be reversed?
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  8. #6
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    Default

    You are doing the math OK. But Keith is right. Your aperture of 114 mm means that the diffraction limit will cause a star to start becoming a disk at 114x. The bands of Jupiter just become wider. The image will begin to blur.

    Under perfect skies your eye may see a little more detail up to about 170x just because the image is bigger.

    You should be looking at FOV and eye relief as much as magnification. My favorite ep is a super plossl with 70 degree apparent FOV and 20 mm eye relief. In my scope that gives me a magnification of 133x with a half degree FOV. I have a 2000 mm fl and an 8 inch (200 mm) aperture.

    But in your scope that would give 66x with a one degree FOV. That would be a good ep for me. I might use that with a barlow occasionally to get the maximum detail the scope can give at 133x.

    But it depends on what you enjoy. If you want to study the details of the moon, you are more likely to want magnification up to 150x. I like faint fuzzies so lower magnification is typical.

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  10. #7
    kencrowder's Avatar
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    Default

    The side question doesn't make sense to me: Would f/6 or larger include f/9 or would it be reversed?

    The f/no is simply the aperture (114 mm) divided into the effective focal length. Yours is 1000/114 = f/8.77. If you put in a barlow it doubles the efl so 2000/114 = f/17.54. Note that the larger the f/no the dimmer the image. Double the f/no will cut the contrast by a factor of 4.

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  12. #8
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    Default

    Quote Originally Posted by WalterK View Post
    32mm=31.25x - is this usable?
    Yes.
    I want to get a Barlow and deciding between a 3x and a 2x.
    The the 3x in same order would be
    600x pointless
    300x pointless
    150x only in excellent conditions
    93.75 x usable


    And 2x would be
    400x pointless
    200x only in excellent conditions
    100x usable
    62.5x usable
    To be honest, I can't see the point of a barlow with the EPs you have. You already have all the magnification your scope is capable of.
    Side question: Would f/6 or larger include f/9 or would it be reversed?
    See Ken's response. I can't tell what you are trying to ask.

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  14. #9
    WalterK's Avatar
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    Default

    One of the barlows I was looking st said it was good for f6 and larger. I was basically wanting to know if f9 was larger or smaller then f6. I in photography f9 would be considered smaller.

    Sorry for the confusion I am so new I am a babbling loony half the time.

    So now I know what I want for my next scope. The more info I gather the stinkier my scope is becoming...lol
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    Default

    A claim like that for a barlow is saying you won't be as happy with it on an f/5 scope as an f/10. It has to do with aberrations around the edge.

    You have a good scope for what it was intended to do. You wouldn't use a sledge hammer to drive tacks nor a tack hammer to break rocks.

    What you have is a scope that is very portable and still gives a good performance for most things. In the future you may get a larger scope, but you will likely continue to use this one quite often.

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