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  1. #1
    1127Tom's Avatar
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    Default 2" VS 1.25" EP = Big Dif?



    Iam looking for some input on spending the extra coin on a 2" ep vs a 1.25"

    I have a Z12 dob. So I assume a 2" ep will pass more light than a 1.25. Is this correct?

    I was thinking of getting a EP dedicated to galaxy viewing so I figured maybe I should buy a 2" one for a "maybe?" better view of dim fuzzy objects.
    Barska 12-60x70 Noc's, Zhumell 12" DOB-->Fully Flocked, Apogee 6"1200fl refractor-CG5, Coronado P.S.T

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    Originally Posted by tglenn
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    Default

    I don't know if the 2" eyepiece makes the image brighter, but it should give you a wider field of view. What I can tell you is that I love the views through my 2" eyepieces! I have 38mm, 30mm, and 26mm for my Z10. If you only get one, I'd suggest something in the 26-32mm range.

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    Antonino Carnevali

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  4. #3
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    Default

    wider FOV is cool. I was thinking of getting the lowest power I can for milky way pan and scaning. I have a 32mm in 1.25"

    I cant recall the equation for figureing lowest usefull power
    Last edited by 1127Tom; 05-30-2010 at 04:35 PM.
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    Originally Posted by tglenn
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    Default

    Quote Originally Posted by 1127Tom View Post
    wider FOV is cool. I was thinking of getting the lowest power I can for milky way pan and scaning. I have a 32mm in 1.25"

    I cant recall the equation for figureing lowest usefull power
    I was going to suggest that. It depends on the size of the exit pupil.

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  7. #5
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    Default

    a 2 in eyepiece is only advantageous with any eyepiece over 25 mm because of the size of the field stop ...

    so ALL of my high power (under 25 mm) are 1.25 inch BUT all of my lower power eyepeices (over 25 mm) are 2 inch eyepieces....

    Bob G.
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  9. #6
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    Default

    Quote Originally Posted by 1127Tom View Post
    So I assume a 2" ep will pass m,ore light than a 1.25. Is this correct?
    The usual notion that 2" EP's "will pass more light" or are brighter than 1-1/4" EP's is brought about by the fact that longer focal length EP's are usually in the 2" format and longer focal lengths generally mean lower magnification/powers which in effect gives a brighter image than higher power magnifications usually yielded by 1-1/4" EP's. A 32mm (1.25") will be just as bright as a 32mm (2") EP, it's just that the 2" EP with its bigger diameter field stop can provide a wide field of view than that of the 1-1/4" EP.

    Use this "Telescope Eyepiece Comparator" to get exit pupil:

    http://scopecalc.grid-itc.com/

    Or just divide the focal lenght of the EP by the f speed of your scope's objective, like for your scope ( Z-12"), a 10mm EP divided by the f-speed 4.7 will yield an exit pupil of 2.1mm.

    Your best bet for bagging those faint fuzzies is to get an EP that gives the best visual acuity for your scope which is generally considered to occur at or around a 2mm exit pupil.

    Best,

    Hernando
    Last edited by ibase; 05-31-2010 at 01:31 AM.

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  11. #7
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    Default

    Thanks for all the good info guys! Very cool.
    Earlier today I saw telescopes.com had a Zhumell 1.25 Inch 8-24mm Zoom Eyepiece for $58 witch was in my price range and I hope it fills the void sorta between my 9mm and 32mm. I have 2x barlow as well. I was feeling like a splurge so I bought an L.P filter as well.

    I guess my next buy will be a low power, wide FOV 2" EP.....
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    Originally Posted by tglenn
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  12. #8
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    I don't think you can go wrong with that. probably similar to my Celestron zoom.
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    Default

    If it helps, the 38mm works fine on the Z10.

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    Antonino Carnevali

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    I use a 32mm 2" on my 10" dob, and I use it every night, and on every target, that I view. I like the wide angle and I use the 2" to star hop. Once I've found my target I go back to the 1.25" EPs and start slowly adding power until I find the magnification I want to use for the night. I just think it is easier to get my bearings and follow the star charts with the 2".
    Rob
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