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Thread: 2 inch Vs 1.25 inch - Which Should I invest in

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    Default 2 inch Vs 1.25 inch - Which Should I invest in



    Hi all,

    I am perplexed on the pro's and cons of 1.25 Vs 2" EP's

    I have an 8" Dob and am fairly new to this...

    Can I please get some direction on why each is better then the other and maybe some direction on what to buy?

    THanks Guys & Gals!

    G./

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    Default Re: 2 inch Vs 1.25 inch - Which Should I invest in

    Here's a good place to start your eyepiece investigation: http://www.astronomyforum.net/telesc...eyepieces.html

    This can be somewhat subjective, as there are more factors than eyepiece/focuser barrel size that need to be considered. For wide-field low-magnification (higher mm, longer focal length) eyepieces, 2" eyepieces can give you the widest field of view. For planetary viewing, where you are really only looking at the center of the field of view, there are only limited benefits to having extra field of view, mainly depending on whether you use a tracking mount or not. If you want high magnification (lower mm, shorter focal length) then you will probably be looking at 1.25" eyepieces.

    Everyone will have an opinion, usually based on their telescope and experience. Eyepiece weight (affects balance), mount, scope focal length, preferred viewing style, preferred targets, etc. all affect these opinions. So, you need to consider what and how you view before choosing any particular eyepiece. That's the reason most of us who've been doing this a while have both 2" and 1.25".

    "Invest in"? If you know how to make money off of eyepieces, please share that secret with me!
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    Default Re: 2 inch Vs 1.25 inch - Which Should I invest in

    Most 2"eps are only available above a given magnification, where you are generally looking for a wider view. That acts as a pretty good guide.
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    Default Re: 2 inch Vs 1.25 inch - Which Should I invest in

    One of the benefits of 2" eyepieces is the capacity to get wide field views at low magnification (or a large exit pupil). The longest eyepiece that can provide even a 50 degree apparent field in a 1.25" barrel is a 32 mm. 2" barrels allow you to go to much longer eyepieces and still have wide fields. One of my favorites is a 40 mm Pentax XL that produces 65 degrees of apparent field. OTOH, higher power eyepieces don't need a large diameter barrel to provide wide fields. I have a more modern Pentax 20 mm with a 1.25" barrel that gives me 70 degrees of apparent field.
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    Default Re: 2 inch Vs 1.25 inch - Which Should I invest in

    As noted... basically inch eyepieces are sold to give you a wider FOV....Every one of my 26 mm and lower powered eyepieces are 2 inch eyepieces BUT every one of my 25 mm and higher power eyepieces are 1.25 mm eyepieces...

    The cut off at 25-26 mm s because the diameter of the eyepiece barrel dictates how much of a FOV you can achieve.. with an eyepiece..and 25-26 mm is the point that you can physicality get a wider light path back to your eye...

    The extra size and especially the extra weight of "some" 2 inch eyepieces can be a disadvantage with some scopes..

    Bob G.
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    Default Re: 2 inch Vs 1.25 inch - Which Should I invest in

    Hello G.

    I second to Bob above. The Antares W70 at f=25mm is possibly the last wide field 1.25" EP in the long focus range, even if not of that quality and design as the wide ES and TeleVue, but these are 2".
    Should you use the nebular and other filters in the future, those sized with 1.25" are much cheaper than those at 2".

    Best,

    JG
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    Default Re: 2 inch Vs 1.25 inch - Which Should I invest in

    If your telescope has a 2" focuser you get to pick whichever size eye piece barrel you want for each eye piece. The trade off between the two is very simple.

    2" Barrel Eye Pieces
    • Required for widest field of view at low power
    • No advantage otherwise
    • Heavier weight


    1.25" Barrel Eye Pieces
    • Lighter weight
    • No advantage otherwise
    • Requires 1.25" adaptor in a 2" diagonal



    If you want a low power wide field of view, you are going to be buying a 2" barrel. The eye pieces only come in 2" barrels because of the wide field of view, not for quality reasons. Every eye piece in this following list of the stated AFOV and focal length (or longer) requires a 2" barrel.

    Requires 2" Barrel
    • 68º 25mm+
    • 82º 20mm+
    • 100º 17mm+



    On the other hand, eye pieces of the stated AFOV that are shorter could come in either 1.25" or 2" barrels depending on the manufacturer and series of eye pieces. The only trade off in picking which barrel size is whether you have to put a 1.25" adaptor on the eye piece and the weight of the eye piece.

    But, if all your eye pieces have the same barrel size you do not need to swap out 1.25" adaptors and you can use the same screw-on filters on your eye pieces. I went with all 2" eye pieces, and have only had to buy my filters in the 2" size.

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    Default Re: 2 inch Vs 1.25 inch - Which Should I invest in

    I like the 2" EP's for the wide FOV. I have a 10" dob and have the ES 30mm 82* EP and the ES 9mm 100* EP which are both 2" EPs. Its really in what you like. Since I like the wide FOV, I chose to go 2". They seem to be a little more pricey, but to me they are worth the extra money because its what I like. They are also bigger and heavier. I have a 2" 2x barlow which doubles my 2" EP collection. The 30mm turns into a 15mm and the 9mm turns into a 4.5mm. I like seeing a lot of space around whatever object i am observing cause its like your looking out of a window into space. If you can, you should attend a local star party and look through all kinds of EP's to find out what you like. 99% of people at star parties will be glad to give you views through different EP's. Its just as much fun showing new people the wonders of the universe as it actually viewing for yourself. They often go out of their way to give you the best views possible for as long as you wanna look. They are usually very friendly people and really enjoy helping out people just getting started into astronomy. Hope this helps.
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    Default Re: 2 inch Vs 1.25 inch - Which Should I invest in

    It,s a personal thing,I love the two inch EP & if i can help it i won't buy a 1.25 again.you can get bigger f.o.v & that helps when your looking for DSO ,& just looking at the stars in that bigger fov is awesome.I love too just point my my scope at the milky,way & with my 14mm ES 100*DEG AFOV, & JUST get lost in a sea of stars & sometimes find a DSO.IF your lucky.lol & sometimes you do.
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    Default Re: 2 inch Vs 1.25 inch - Which Should I invest in

    Bob pretty much hit it. Once you get to a certain focal length of eyepiece, having a 2 inch barrel is irrelevant. As you get shorter in f/l, the light cone coming to your eye narrows to the point that a 1.25 inch barrel can contain it without attenuation. Unless you have a really super wide field (such as 100° AFOV), then there is no need to go 2 inch below a certain focal length because you are just paying for extra metal and glass that you don't need. For example, in the ES 82 series, the 18mm is 2 inch, but the 14mm and shorter are 1.25. For the real low powered wide-field views, you need to go 2 inch to make certain that the entire light cone is being passed to your eye.
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