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  1. #1
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    Default Does size matter (eyepieces)?



    Greetings,

    I have 10mm, 20mm, 26mm eyepieces and a 2x Barlow. And I have been taking photos with film and a digital camera for many years, sp I am familiar with lenses.

    The camera lenses (telephoto and teleconverter) bring objects closer, but that doesn't seem to be the case with the telescope eyepieces.

    I have searched a couple forums and have hit upon some answers to my question, but they quickly get into other parameters and calculations that I don't understand (yet). I have to take little steps and, being a graphic-oriented person, verbage doesn't always inform me as much as confuse me.

    Here's the question: When searching for something, which lens is best (I am still doing manual searching/panning because I have not performed the two orientation procedures). If I want to see something closer, or clearer if a DSO, which lens should I switch to?

    thanks, in advance,

    len
    ======================
    Meade ETX 90MM Cassegrain
    Celestron 114 FirstScope EQ

  2. #2
    sxinias's Avatar
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    Default

    See something closer or clearer; which eyepiece to use? We can only talk generalities here because of the multitude of objects, viewing conditions, and optical parameters.

    The numbers you mentioned that describe your eyepieces are the focal lengths of the eyepieces. Generally speaking the longer the focal length of the eyepiece (larger number), the smaller and sharper the image; the shorter the focal length of the eyepiece (smaller number), the larger and less clear the image. However, having said that, in general as you magnify an image (go from long focal length eyepiece toward shorter focal lengths), you start seeing more details at the expence of sharpness until you reach a point where fuzzyness overcomes details making further magnification non-productive.

    The other aspect of eyepiece focal length is the longer the focal length the wider the field of view in any particular telescope. So when searching for an object, an eyepiece with long focal length will show a wider field of view making the task of spotting an object easier. After you have found an object, then what eyepiece to use next is really dependent upon the object, the light gathering capability of the telescope, and personal preferences as well as viewing conditions...... experience.
    Last edited by sxinias; 04-19-2010 at 05:07 AM. Reason: added as well as viewing conditions
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  3. The Following 4 Users Say Thank You to sxinias For This Useful Post:

    carnevali (04-19-2010),Dublin sky watch (04-19-2010),Hugh (04-19-2010),WWPierre (04-19-2010)

  4. #3
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    Default

    Thanks Sxinias, That was a help to me too.
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    Default

    What kind of telescope, Featherdealer?
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    Default

    That was a really helpful answer, thanks bunches!

    And it sure explains why I was confused when things (like Saturn) weren't getting any closer when I used a longer focal length (26mm) and why I thought I was seeing "deeper" (i.e. more stars) with the longer focal length, when, in actuality,I was seeing a lager FOV.

    I will assume the 2x Barlow doubles the focal length unless you tell me otherwise.

    The relationship between focal length, FOV and magnification will confuse me for a little longer, but now I have a clarification to keep near my telescope stuff.


    thanks again, sxinias,

    len (aka FeatherMerchant)

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    ======================

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    Default

    NOPE...the Barlow does exactly the opposite turning your 26 mm eyepiece into a 13 mm (more powerful ..more magnification...) then the eyepiece normally delivers when used alone...

    Bob G
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