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  1. #1
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    Default Best size eyepieces for Orion Xt6 1200mm



    What size eyepieces do you all recommend for an Orion Xt6 dob with 1200mm focal length. The telescope comes with a 25mm eyepiece. I understand a 4mm eyepiece will be at the highest useful magnification (300x) for this telescope. Now if you have a barlow with an 8mm eyepiece, the telescope will be at 300x as well right? But there are so many other sizes to choose from. I just want to know what sizes would go well with a telescope with 1200mm focal length that will give you a nice assortment on different magnifications. Is it important to take focal ratio into consideration as well?

    Thanks for all your help so far, I just joined and could not be happier with everyone on the forum!

  2. #2
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    TCA
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    Forget the 4mm, it will never get used. The "highest useful magnification" is what the scope could theoretically do if the sky was perfect, which it typically never is. I'd get a decent barlow and use the 25mm, which with the barlow is also a 12.5mm. You can get a 32mm for low power with the barlow will become a 16mm. I wouldn't go below double digits, an 8mm tops for better than average nights...a 16mm or 17mm barlowed.

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  4. #3
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    another alternative to getting seperate ep's right now
    is to get an 8-24mm zoom.
    why?because it will cost you about the same as two half decent
    ep's but gives you a whole lot more choice.
    they are available from all the main manufacturers.you could go
    a little bit more expensive and get the hyperion zoom,which MANY
    people have,and rave about.
    the only slight drawback would be the fov,not the same as you would
    get with some of the lower power ep's,but very good,and very usable.
    it will also help you learn which power ep you use the most if you
    decide to get single ep's later on down the line.
    hope this helps.
    clear skies,
    andy

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    andy

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    ARCHAEOLOGISTS WILL DATE ANY OLD THING

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    I got a 17mm Sterling from Smart Astronomy for $30. I like it a lot. For your scope, that would be a nice step down from the 25mm.

    However, you might prefer a little more magnification, say, a 14mm or 15mm.
    Fly me to
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    120mm refractor, non-go-to mount, eyepieces are 40mm and 32mm Orion Highlights, 25mm and 10mm Orion stock, 17mm Sterling, 12.5mm Baader, and 7.5mm Orion Ultrascopic, all housed in 8X10 Sky Shed

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    The focal ratio is used to calculate your exit pupil (EP focal length / focal ratio). Most documetation will state that the maximum exit pupil should be 7mm but most people will tell you that an exit pupil between 4 and 6mm is more realistic. When in total darkness and at a younger age your pupil may dialate to 7mm, that's why the smaller exit pupil is more realistic.
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  10. #6
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    Quote Originally Posted by Marshifty View Post
    I just want to know what sizes would go well with a telescope with 1200mm focal length that will give you a nice assortment on different magnifications. Is it important to take focal ratio into consideration as well?
    Well, yes the focal ratio of a scope can be used as a determinant in eyepiece (EP) selection. Your scope has a focal ratio of F/8. What's the best focal length for this focal ratio? If you want the sharpest and clearest view that your scope can provide then get a 16mm EP. Why? It is generally regarded that an EP that yields an exit pupil (the circular ray of light that exits from the EP eye lens) of at or around 2mm will provide the best visual acuity for any scope. To get the EP that will yield that, just multiply your scope's speed by 2mm (8 X 2mm = 16mm), or a 16mm EP which when used with a 2x barlow gives the equivalent of an 8mm EP, a good hi-magnification focal length to use during those nights when the "seeing" is good (meaning stable atmospheric conditions to allow for bumping the power up).

    But if you want the ultimate EP, go with Andy's suggestion and get the Hyperion 8-24mm zoom; this zoom is almost of universal use, I've come across owners of both slow and fast scopes (from F/10 to F/5) who are very happy using it, some even employing just this single variable-focal lenth zoom EP; and the good thing is that scopes can come and go, but a Hyperion zoom can be forever! (p.s. I have 60+ eyepieces and the HypZoom is my favorite to use.)

    Best,

    Hernando
    Last edited by ibase; 12-21-2010 at 02:16 AM.

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  12. #7
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    Awesome advice thanks guys! I will definitely save up for that Hyperion Zoom, sounds like a great EP.

 

 

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