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Thread: Scope and eyepiece size, doing the math

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    Lightbulb Scope 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 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: Scope and eyepiece size, doing the math

    For several years I did astronomical observations with an ETX125, but now I have two more telescopes, the 8LX90 since the beginning of the year and from the last month the Zhumell 12; and I hope these words will help you.

    1) more magnification is always better (?), Well I think there is not an easy answer. With wide angle views you got an incredible experience.... but...Think of Helix nebulae and try to relate its dimension to the integrated magnitude, then apply this relation to M 57 as a comparison; of course no single eyepiece is the optimal solution for both cases. For instance, small DSO allows high power eyepieces in order to darken the sky background. Otherwise large DSO as M 33 or M31 under low power wide angle eyepiece looks terrific.

    2) Your selection seems good for all DSO. They cover a wide variety of exit pupil and magnification.

    3)Binary stars and planets needs small FL eyepieces and the barlow. But I think the best option is an orthoscopic low FL eyepiece and no barlow; and maybe you save some $$.

    íCongratulations for your intelliScope! so many hours of DSO delights.

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    Default Re: Scope and eyepiece size, doing the math

    You might find this thread useful, plenty of good info: Article: What Astronomy Eyepieces should I get for my Telescope?
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    Default Re: Scope and eyepiece size, doing the math

    1) No. One wants to frame objects of very different size and brightness. Maximum contrast provides the best view of DSOs. Difficult objects like the Horsehead Nebula need an exit pupil of 5mm (and a great transparency night) for instance.
    2) I favor Tele Vue Panoptics but your selection is adequate and cost effective for DSOs. For planets I'd add the Baader BCO Q turret set which comes with a very nice
    3) 2.25x barlow.

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    ST80 (mods for white light solar), SV ED80 f7 Newtonians: Z12 f5 Catadioptrics: VMC110L, Intes MK66 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binocular Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker III, Vixen Porta II, Celestron CG5, Orion
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    Default Re: Scope and eyepiece size, doing the math

    Welcome to the forum! Many factors are in play when you selecting EPs for the target, and no, higher power is not always better. The theory could get complicated, but application is simple: have a range of several EPs, start at low power and keep switching EPs to shorter FL until you find the best view. With time you will become more efficient, but even now when I hit a difficult target I could try 10+ EPs to get the best view.

    You are already to a very good start: you got a nice range of good quality EPs, which perform well on all kind of targets. Start observing, and don't rush in buying more stuff until you gain more experience and develop observing preferences.
    j.gardavsky and SpyderwerX like this.

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    Default Re: Scope and eyepiece size, doing the math

    Thank you all for great insights and feedback. cheers...

 

 

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