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  1. #1
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    Default "Upgrading" power with eyepieces?



    Greetings. I am new here with a noob question about eyepieces.

    I am considering purchasing either the Celestron 114EQ or 130EQ, both popular and well known telescopes. I am not a true beginner however; I know my way around the night sky and have used scopes before (though sparingly).

    I really like the fact that the 130 has more aperture, but the difference in focal length between the two concerns me somewhat (1000mm in the 114, 650 in the 130).

    But, if I am correct in my thinking, the shorter focal length of the 130 can be "corrected" or "upgraded" by using more powerful eyepieces, correct? In other words, I can get the 130, and an additional eyepiece (or Barlow) and be equivalent to or better than the comparative focal length of the 114. Am I correct in my thinking?

    Are there disadvantages to this? Would a 1000mm raw focal length image be any better than a 1000mm "adjusted" focal length image (by adjusted, I mean a shorter raw focal length with enhanced eyepiece)?

    Thank everyone! I look forward to being a part of this community (and harassing you with my questions).

  2. #2
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    The telescope focal length determines the fundamental image scale, or size of the image formed at the focal point/field stop.

    A longer focal length telescope forms a larger image than a shorter focal length scope.

    In turn, the image scale influences the degree to which the eyepiece's field lens/eye lens combination can magnify the image for use by the eye.

    The larger the image scale of the initial image formed by the telescope, the more magnification one is able to produce with the eyepiece without degrading the image. This is a function of focal length (image scale) and aperture.

    Within limits, it is possible using an eyepiece, or combination of eyepiece and Barlow to create the same effective magnification with the shorter, 650mm scope as one would get with the 1000mm instrument. In this case, because the aperture is increasing (i.e. 114mm -> 130mm), the smaller image scale won't be significantly degraded by increased eyepiece magnification. This would not be true without the aperture increase.

    In short, you're better off with the 130mm scope over the 114mm scope, even though its shorter in terms of focal length.
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    Seldom can I add to Austin's posts, but it should be noted that slower scopes are more forgiving of eyepiece quality, although there are some very reasonably priced EPs that perform very well in faster scopes.
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    Any suggestions as to what are some good eyepieces? I seem to have a "faster scope" with XT6. We have some the Plossl eyepieces that Orion offers...should we have got something better?
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  7. #5
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    Celestron 114EQ or 130EQ?

    Select the 130EQ. Why?

    The AstroMaster 130EQ is a classical Newtonian Telescope design while the AstroMaster 114EQ is not a true Newtonian but a Jones Bird design variation with a spherical mirror, a built-in corrector/barlow lens, and can be very difficult to collimate.

    If you go to the Celestron Specs page for the 114EQ, you will notice that it has a focal length of 1000 mm but its tube length is only 508 mm. The missing distance is provided by the built-in barlow lens so to speak. This design is not necessarily bad and many people who have this type telescope are happy with its performance. However, many aren't and find collimating them very difficult to impossible to do.

    The 130EQ is a true Newtonian with a parabolic mirror and will have none of the issues associated with the Jones Bird newtonian design variation. It has a focal length of 650 mm and a tube length of 609 mm. The tube is slightly shorter than the focal length because some of the focal length is the distance between the secondary mirror through the focuser to the eyepiece.

    The Jones Bird design can produce excellent telescopes such as the Vixen "modified" cassegrain telescopes.
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  9. #6
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    Quote Originally Posted by sxinias View Post
    Celestron 114EQ or 130EQ?

    Select the 130EQ. Why?

    The AstroMaster 130EQ is a classical Newtonian Telescope design while the AstroMaster 114EQ is not a true Newtonian but a Jones Bird design variation with a spherical mirror, a built-in corrector/barlow lens, and can be very difficult to collimate.

    If you go to the Celestron Specs page for the 114EQ, you will notice that it has a focal length of 1000 mm but its tube length is only 508 mm. The missing distance is provided by the built-in barlow lens so to speak. This design is not necessarily bad and many people who have this type telescope are happy with its performance. However, many aren't and find collimating them very difficult to impossible to do.

    The 130EQ is a true Newtonian with a parabolic mirror and will have none of the issues associated with the Jones Bird newtonian design variation. It has a focal length of 650 mm and a tube length of 609 mm. The tube is slightly shorter than the focal length because some of the focal length is the distance between the secondary mirror through the focuser to the eyepiece.

    The Jones Bird design can produce excellent telescopes such as the Vixen "modified" cassegrain telescopes.
    This is all new information to me that I did not realize. I assumed they were both true Newtonians. Thanks a million!

    I was leaning to the 130 anyway because of the aperture. I just wanted to make sure I could make up the focal length with eyepieces if necessary.

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    Quote Originally Posted by cmcfalls View Post
    This is all new information to me that I did not realize. I assumed they were both true Newtonians. Thanks a million!

    I was leaning to the 130 anyway because of the aperture. I just wanted to make sure I could make up the focal length with eyepieces if necessary.
    The larger aperture of the 130 comes on top accross the board.

    The 130 mm scope gathers 30% more light than the 114mm scope. Its highest usefull magnification is 307x vs 269x, limiting stellar magnitude 13.1 vs 12.8, Rayleigh resolution (details of objects) of 1.07 vs 1.22 AS; Dawes resolution (double stars) of 0.89 vs 1.02 AS and light gathering (ratio of light gathered vs dialated eye) power of 345x vs 265x ...... The 130 also come with the heavier CG3 mount and tripod but is heavier at 28 pounds (12.7 kg) while the 114 weighs 17 pounds (7.7 kg).
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    I agree completely BUT I wanted to say that I was confused by Austins use of the words image scale...

    I understand what he said BUT I want to warn you that he did not mean the size of a target (like Jupiter) will appear to your eye....

    100x is 100x no matter how you cut it...

    The fact that the 1000 mm scope gives you 100x with a 10 mm eyepiece and the 650 mm scope gives you 100x with a 6.5 mm eyepiece makes no difference..

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    Quote Originally Posted by LawofKato View Post
    Any suggestions as to what are some good eyepieces? I seem to have a "faster scope" with XT6. We have some the Plossl eyepieces that Orion offers...should we have got something better?
    Check out this thread at Cloudy Nights: Telescope Reviews: Til I Saw Her Face, Now I'm a Believer!

    Also check out Harry Siebert's eyepieces. Possibly the best oculars for the money. Siebert Optics - Home Page

    You are aiming for a range of eyepieces that will cover the theoretical capabilities of your scope, lowest magnification, (important) to highest (not so much)

    If you have astigmatism, look for high eye relief oculars, because you need to keep your glasses on. Near and far sighted folks can observe without their glasses.
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