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Thread: Telescope and eyepiece size, doing the math

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    Default Telescope and eyepiece size, doing the math



    Hello, I'm new to astronomy and looking to get useful insights from you experts here. I just ordered the Orion XT10i dob, and also ordered the ES82 series set of eyepieces 30mm, 18mm, 11mm, 6.7mm. Have a few questions:
    1. Given a certain size of Aperture, Focal lengths of scope and eyepieces, is it fair to say that as long as TFOV is similar across different eyepieces of different angles, then its better to go with highest magnification? In other words, if i have a high power eyepiece with big view angle, and a lower power eyepiece with smaller view angle, then might as well go with the first one, as my TFOV will be the same and i guess more magnification is always better (?)
    2. Please provide your recommendation on my eyepieces, if they will cover the full range of DSO, planets.
    3. Also please suggest a good 2x barlow

    Thanks in advance.
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    Default Re: Telescope and eyepiece size, doing the math

    Hi Biggerstrides, and welcome here to the Forum!

    Congratulations on your new scope! That selection of eyepieces seems to be good to me.
    Others here with more knowledge than me will come by and offer their advice.

    Good luck, and clear skies!

    smp
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    Default Re: Telescope and eyepiece size, doing the math

    Welcome. Generally my suggestion is to use the lowest power eyepiece to find an object and then ratchet up the power to see more detail and darken the sky background. No levels of power are "better" than others. Lower powers offer wider fields of view and hence are preferred for locating objects you wish to observe. I find the ES 18mm eyepiece to be the "sweet spot" for overall observing - some magnification but still a wide field of view.
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    Default Re: Telescope and eyepiece size, doing the math

    Hello, and welcome aboard!

    I concur with Michael that the usual recommendation is to start with the least magnification first, and then dial in the desired view. The amount of magnification you will be able to use varies a lot by the target itself, and also by the sky and atmospheric conditions. The ES eyepieces are very good, and very highly regarded and will serve you well.
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    Default Re: Telescope and eyepiece size, doing the math

    Welcome to the forum and thanks for joining us!

    A great guide here to consider: Article: What Astronomy Eyepieces should I get for my Telescope?

    Your best bet is to not worry about TFOV or AFOV or even magnification. Let exit pupil be your ultimate guide in the selection of eyepiece focal lengths. Magnification is merely a secondary happenstance that follows along with exit pupil. AFOV is a matter of personal taste and has no bearing on power or exit pupil. TFOV is a product of scope focal length and eyepiece focal length and AFOV. It is also a secondary factor. Exit pupil is the thing to consider.

    Bryan

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    Default Re: Telescope and eyepiece size, doing the math

    What Frainkie and Michael said. You have a very nice scope and some pretty darn good eyepieces. Use them all! Just remember the higher the magnification the dimmer the object will be. Also remember what you're looking at, big objects require less to see more.

    Clear skies,
    Bob
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    Default Re: Telescope and eyepiece size, doing the math

    Welcome!
    What they said!
    Clear skies,
    Jeff

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    Default Re: Telescope and eyepiece size, doing the math

    Welcome and that's a great way to start as the ES lenses are great I too find the 18mm 82° EP to be the "sweet spot" as Micheal put it Just be forewarned regarding the 30mm EP as it's a 35 oz beast - I always refer to it my "pineapple"

    Good luck!
    Abb
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    Default Re: Telescope and eyepiece size, doing the math

    Hi there, Welcome to the forums!

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    Default Re: Telescope and eyepiece size, doing the math

    Hi Biggerstrides. You have to remember that the True field of view is equal to the eyepice Apparent field of view divided into the magnification of your instrument. For me, I like my ES 18mm 82 degree eyepiece with my f/5 refractor and my f/4.9 Dob reflector. For Lunar and planetary viewing, the maximum I can get from my Mak-Cass is with a 9mm, due to it's long focal length (f/15). I hope this helps Biggerstrides, and welcome to the forum.
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