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Thread: Which Eyepiece for Which Scope

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    Default Which Eyepiece for Which Scope



    My question revolves around telescope types (refractor, reflector, SCT, etc) and the best type of eyepiece to use for it. For example I have a 8" SCT and I need a new wide angle 30 - 40 degree eyepiece. Would I be better off with a Plossl or an Ortho or something else? This is something that I want to get right in that I don't want to invest in eyepieces that aren't the right "fit" for getting the best out of the OTA. Any help with this is very much appreciated.

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    Default Re: Which Eyepiece for Which Scope

    Quote Originally Posted by Asterion View Post
    For example I have a 8" SCT and I need a new wide angle 30 - 40 degree eyepiece.
    I assume you mean you need a new, wide angle 30mm-40mm eyepiece.
    Rob

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    Default Re: Which Eyepiece for Which Scope

    That plus just an overall general knowledge of type of eyepiece/type of scope combinations. For example will a Plossl be the best choice for a SCT or for a refractor. Or doesn't it make any difference and use what you want...

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    Default Re: Which Eyepiece for Which Scope

    It is entirely down to personal choice and funds. No one type of eyepiece could be said to work better in any one type of telescope.

    Some may argue that, for instance, an orthoscopic eyepiece works better in refractors (and you should see some of the arguments!)

    As a general rule, for all types of telescope, the majority of people prefer a wider angle eyepiece, with those between 68 degree and 82 degree the most popular.

    In your particular case, and assuming you can use a 2" eyepiece, then something like an Explore Scientific 82 degree 30mm or a Televue Panoptic 35mm would give great views. There is a wide choice out there , and most eyepieces these days are of a very high standard.
    Last edited by hal2000; 12-18-2015 at 11:32 PM.
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    Default

    A lot is down to personal preferences (and budget). At f10, an SCT is a relatively slow scope, so most eyepiece types will work well. With faster scopes (small f-ratio numbers, like f5 or less), the light reaches the eyepiece over a wider range of angles, which puts more demands on the eyepiece.
    One drawback with most basic eyepiece designs is that they are scaled designs - so to produce a shorter focal length eyepiece (higher magnification), you just scale the optics down.
    Unfortunately, that also reduces the eye relief, so you have to put your eye closer - which can be a problem if you wear glasses (though you can usually just refocus without glasses unless you have significant astigmatism).

    Premium eyepieces are more expensive, but can offer several advantages.
    By varying the design, they can maintain a decent eye relief (and a large eye lens) even at short eyepiece focal lengths - which can make them more comfortable to use.
    They can also offer a wider apparent field of view (size of the circle you see the image in) which lets you see more of the sky at the same magnification. Typical plossls run around a 50° AFOV, while premium designs go noticeably larger (typically around 68°, which is a significant increase). You can also get ultrawide AFOV eyepieces, 82° or 100° or more - with these the circle you see the image in is a lot larger, so much so that you don't really notice the background any more and have to look around to see everything.

    The only real limitation on eyepiece type choice is the speed (f-ratio) of the scope - I have a budget 2" 80° 30mm eyepiece that works fine in a slow scope like an SCT, but struggles in faster scopes - as the scope gets faster, and light arrives over a wider angle, the view at the edge deteriorates - the faster the scope, the worse the distortion gets, and the further in it goes.
    j.gardavsky likes this.

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    Default Re: Which Eyepiece for Which Scope

    That's a lot. I'll look for an eyepiece that fits my needs vs a specific style.

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    Default

    One other thing I forgot to mention - some scopes allow you to use either 1.25" or 2" barrel eyepieces.
    At high magnifications, you're just magnifying the central bit of the image formed by the scope. As you decrease the magnification (by increasing the eyepiece focal length) or increase the AFOV, you see more of the image formed by the scope - and eventually the size of the eyepiece barrel becomes a limiting factor, when you're seeing all of the image that will fit inside the barrel. To see more, the eyepiece design needs to use a larger barrel - that's why a 2" 40mm eyepiece can have a larger AFOV (around 68°) than a 1.25" 40mm (around 45°) , and why many of the ultrawide AFOV eyepieces (for 82°, around 17mm and longer) are only available as 2" eyepieces.
    The wider possible view is the only optical benefit of 2" eyepieces - they just let you fit more image in around the edge - but that wider view makes them most people's preferred choice for low power / wide field views with scopes that support them.
    For views that fit into a 1.25" barrel, a 1.25" eyepiece is fine - and a 2" has no optical benefit. (Some 1.25" eyepieces have a dual barrel or a 2" lower body, so you can use them directly in either size focuser - but it's just as easy to use a 2" holder to 1.25" eyepiece adapter.

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    Default Re: Which Eyepiece for Which Scope

    What I'm looking at is a 28-34mm eyepiece. So many if the style/type of component doesn't make a difference I can choose based on parameters like cost, size, etc. Thanks for all of the help.

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    Celestron AVX EdgeHD 8" SCT, Featertouch FTM-CPC8 Focuser, ADM Dual-VX Saddle with ADM Vixen dovetail bar, EdgeHD .7 Focal Reducer, Celestron StarSense Autoalign, WO DDG SCT Rotolock Focuser, Telrad Finder, ES 82deg 30mm-18mm-11mm-6.7mm eyepieces, Baader Hyperion Zoom Lens, Hyperion 2.25x Barlow Lens, Baader 2" SCT Visual Back w/Filter Holder, ASTF-200 Solar Filter, various filters, assorted accessories and a Nikon D7100.

 

 

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