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Thread: Eyepieces for Maksutov-Cassegrain telescopes

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    Default Eyepieces for Maksutov-Cassegrain telescopes



    Hi,

    I'm still a beginner and have a question about eyepieces. I just purchased an Orion 6" Maksutov-Cassegrain scope and understand that, by design, these scopes have a long focal ratio (mine is f/12) which produces a higher magnification with a given eyepiece but a narrower field of view than with an f/10 Schmidt or f/6 or f/8 Newtonian.

    That said, my scope will also take 2" eyepieces. Can I get around the narrow field of view with a 2" eyepiece or am I bound by the long focal ratio?

    Thanks!

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    Default Re: Eyepieces for Maksutov-Cassegrain telescopes

    From what I know, you can calculate the field of view (FOV) this way:

    FOV = eyepiece field of view/magnification.

    The magnification obviously depends on your telescope focal length, just like you said. In your case, you'd be getting twice the magnification of a 6" f/6 telescope.

    The eyepiece field of view depends on which eyepiece you buy. Usually, stock 1.25" eyepieces will have a 52 degree FOV. Maybe a bit more. With an f/12 telescope, you'd be pretty bound by your long focal length. But if you have the budget to go higher, you can find some 1.25" eyepieces with a 66 degree field of view, or even higher (up to 82 I think). That would give you a bit more room to work.

    For the 2", since they are bigger eyepieces, you have more room to work with. Some of these have upwards of 100 degrees of field of you. So for example, if you used a 18 mm eyepiece (with an eyepiece field of view of 100 degrees) on your telescope, you would have:

    magnification = focal length/eyepiece length = 1800/18 = 100x
    FOV = eyepiece field of view/magnification = 100/100 = 1 degree --> that's pretty wide. It fits the whole moon and more.

    So yes, you can get around the narrow field of view, but the eyepieces will be a bit more costly. That being said, you'll be getting quality stuff
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    Default Re: Eyepieces for Maksutov-Cassegrain telescopes

    Most of CATs and MAKs are limited by design to ~1 degree max apparent field of view. But as Paulsz says it is still more then enough for most targets, other than a few extra large.

    2" EPs with FOV in 65-82 degree range are very useful. Another approach is to get 0.63 focal reducer for Mak/SCT which will reduce your scope focal ratio to F7.6
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    Default Re: Eyepieces for Maksutov-Cassegrain telescopes

    If I had the scope I would have a focal reducer and use the ES 82 EPs. That will open things up about as far as you can go with the scope and will give you excellent views.
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    Default Re: Eyepieces for Maksutov-Cassegrain telescopes

    Thanks, that was a great explanation - very helpful!

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    Default Re: Eyepieces for Maksutov-Cassegrain telescopes

    Thanks for that suggestion!
    Equipment: Orion StarSeeker IV 150mm GoTo Mak-Cass Telescope, Celestron 8x42 binoculars, Canon Rebel T1i
    Lenses: Orion 32mm Sirius Plossl , Orion 12.5mm Sirius Plossl, (Svbony 23mm wide-field eyepiece, Svbony 10mm eyepiece - came with scope), Accessories: Orion Shorty 1.25" 2x Barlow, 1.25" Orion Variable Polarizing Filter

 

 

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