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Thread: Using the 2 inch or 1.25 barrel on 8inch Dobsonian?

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    Default Using the 2 inch or 1.25 barrel on 8inch Dobsonian?



    Wondering if there is an opinion out there on using different barrels for my telescope. My wife wants to by me a kit of eyepieces. I most use my tscope foe planetary although would like to view globular galaxies. Should she buy 2 inch kit or can you by kits that contain lenses for both barrel diameters.

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    Default Re: Using the 2 inch or 1.25 barrel on 8inch Dobsonian?

    This will depend on the barrel size of the focuser on your dobsonian. If you have a 2" focuser, you can use both 1.25" and 2" eyepiece sizes with your scope with the proper adapter. Typically, scopes with a 2" focuser come with this adapter.

    If your scope had a 1.25" focuser, you won't see any benefit with trying to use an adapter to accommodate a 2" eyepiece. You get vignetting and will not realize the full potential of the 2" size. Only way around that is to change out the focuser.

    So, what size focuser do you have?
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    The advantage of a 2" barrel is that it allows for wider field of view eyepiece designs at low magnification.
    At high magnification, you're only looking at the central part of the image formed by the scope. As you reduce the magnification (by using a longer focal length eyepiece) , or use an eyepiece with a bigger apparent field of view (size of the circle you see the image in) at the same magnification, you see more of the image formed by the scope.
    Keep going, and eventually you see all the image that will fit in a 1.25" barrel. To see more than that, you have to switch to a 2" design - that's why some eyepieces are only available as 2" designs.
    If the image will fit in a 1.25" barrel, there's no optical benefit to using a 2" eyepiece.
    Most of the eyepiece kits tend to use standard scaled eyepiece designs, like plossls. One limitation of scaled designs is that the eye relief (how close you have to put your eye to the eyepiece) gets shorter as the focal length decreases (for higher magnification).
    If your main interest is planetary observing, at high magnification, you might find one of the more complex eyepieces with a bigger eye relief and eye lens more comfortable to use.
    But for low power wide field views, most of us who can use 2" eyepieces in our scopes prefer them due to the wider views they allow.

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    Default Re: Using the 2 inch or 1.25 barrel on 8inch Dobsonian?

    Quote Originally Posted by bladekeeper View Post
    This will depend on the barrel size of the focuser on your dobsonian. If you have a 2" focuser, you can use both 1.25" and 2" eyepiece sizes with your scope with the proper adapter. Typically, scopes with a 2" focuser come with this adapter.

    If your scope had a 1.25" focuser, you won't see any benefit with trying to use an adapter to accommodate a 2" eyepiece. You get vignetting and will not realize the full potential of the 2" size. Only way around that is to change out the focuser.

    So, what size focuser do you have?
    Thx I will have to check but I'd say from the look it is a 2" focused with an adapter to fit the 1.25

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    Default Re: Using the 2 inch or 1.25 barrel on 8inch Dobsonian?

    I think most of 8" DOBs come with 2" focuser. You should be all set for both sizes

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    Default Re: Using the 2 inch or 1.25 barrel on 8inch Dobsonian?

    I don't claim to know much so far, but 2" eyepieces seem to be expensive enough that I'd hate to see the smaller MM sizes go to waste in a 2" barrel when you are doing planetary observing. It's hard to know, but perhaps careful selection of a few in both sizes might accomplish your goal at a lower cost? Good luck!
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    Default Re: Using the 2 inch or 1.25 barrel on 8inch Dobsonian?

    Quote Originally Posted by COMtnSkies View Post
    I don't claim to know much so far, but 2" eyepieces seem to be expensive enough that I'd hate to see the smaller MM sizes go to waste in a 2" barrel when you are doing planetary observing. It's hard to know, but perhaps careful selection of a few in both sizes might accomplish your goal at a lower cost? Good luck!
    There are some cheap 2" EPs... But yes for the same level 2" EPs tend to be more expensive. However, you don't need many and obviously not for the planetary observing. You only need 2" EPs if you would like to get wider FOV at lower magnifications.
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    Default Re: Using the 2 inch or 1.25 barrel on 8inch Dobsonian?

    The kit below would be first rate and good value, but if you're in Brisbane Australia (and not Brisbane California) the dollar won't make this so cheap as I don't know anyone is Australia who does this kit :-/
    82° Eyepiece Kit | Explore Scientific USA
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    Default Re: Using the 2 inch or 1.25 barrel on 8inch Dobsonian?

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    Default Re: Using the 2 inch or 1.25 barrel on 8inch Dobsonian?

    Most telescopes come with a couple of eyepieces.Usually something around 24-25mm and a 9-10mm.
    In general eyepiece kits with an assortment of different size Plossl eyepieces and an assortment of color filters. There is nothing great or nothing bad in these kits, they are just average. But you will find that you will only be using two or three of eyepieces in total from what you have plus the kit and probably none of the filters. If you only buy 1 or 2 eyepieces you can step up to some better quality eyepieces.

    The Explore Scientific kit contains some very nice eyepieces, but it is fairly pricey. It contains eyepieces of both barrel sizes.

    Below roughly 13-15mm you are fine with 1.25 inch eyepieces. Above that I would recommend 2 inch ones. Yes they are more expensive, but it does make a difference.

    First off, I would invest in a decent quality 2X barlow. This will effectively double your eyepiece collection. Your 25mm will act like a 12.5mm and your 10mm will act like a 5mm, when you use the barlow with them. Next I would try and find an astronomy club and go to some of their out reach events, viewing sessions or star parties and look through other people scopes and eyepieces. Heck, one or two may even let you try an eyepiece in your scope. Then when you find one or two that you like, buy them. If there are no clubs around then just guessing that you have a 10mm and 25mm I would suggest you look at something around 17mm and 7mm. What kind of scope do you have? This will make a difference as to what you should get.
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