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  1. #1
    jakeyseven's Avatar
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    Default magnification of e pieces



    hello i am new to telescopes but i would like to know , when i use a 25 mil e/p it allows alarger light source , but when i use a higher mag like a 6 mil there is less light entering. can you help with this one cheers

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    Default

    Well, Jakeyseven, even though I am relatively new to this stuff as well, I will try to answer your question. Your telescope will deliver a given amount of light to your secondary mirror(reflector type), that amount being dependent on the size of the primary mirror--the bigger it is, the more light it gathers. Now, if you use a less powerful EP, say a 25mm, you will see a given area on the secondary, with a given amount of light. If you switch to a more powerful EP like a 9mm, you will now be expanding that first area that you were seeing, and its light level, to a wider level. The amount of light has not changed, but it is now spread out over a larger area, so the light intensity is less.
    Kinda like comparing a gallon of water in a 1 ft round bucket to it being in a 2 ft round bucket. The water depth will be much less in the bigger bucket.
    At least that is how I see it.
    Helios 200P f5 Reflector on EQ5 mount and aluminum tripod--1.25 Plossl 10 & 20 EP's with 2X
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    5SE + 1.25" EP Kit

  3. #3
    Joe Lalumia's Avatar
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    THE HIGHER the magnification THE DIMMER the image in the eyepiece.

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  4. #4
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    When you use a longer focal length eyepiece, such as a 25mm, you have a wider field of view and less magnification. Thus a given object will appear smaller, with it's light concentrated into a smaller area, making it brighter. When you go to a shorter focal length eyepiece, such as a 9mm, you have a smaller field of view and higher magnification. The given object's light is then spread out over a larger area, making it appear dimmer to your eye.

    Therefore as Joe said, the 25mm will make the image brighter as compared to the 9mm.
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