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    Cool TeleVue Nagler 9mm



    Recently purchased a Celestron 10" dob. Wanted a premimum eyepiece so I got a TeleVue Nagler 9mm. It is of course a 1.25" eyepiece and as expected views are darker than my 32mm 2" eyepiece. However, when focusing on a really bright start, I am seeing a (photographic term ahead) 4 point star filter effect, i.e. there are 4 rays that spread out in 4 directions from the bring element accross the entire FOV. Is this normal? Or did I get a bad eyepiece?

    Thanks for any response.

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    Those 4 points of light you are seeing are the vanes of the spider holding your secondary mirror.
    Quite common with Dobs.

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    Yep! - Diffraction spikes.
    You'll see them wth any reflector that has a 'spider' support for the secondary mirror.
    The finer, and sharper they are, the better your optics.
    Smaller reflectors, with only 3 vanes to the spider, will show a 3-point star effect.

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    I don't find this a major problem, but some have gone to the trouble of mounting a curved secondary holder to reduce this effect..


    Single-arch Curved Secondary Mounts

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    Default

    Quote Originally Posted by philip d View Post
    Recently purchased a Celestron 10" dob. Wanted a premimum eyepiece so I got a TeleVue Nagler 9mm. It is of course a 1.25" eyepiece and as expected views are darker than my 32mm 2" eyepiece. However, when focusing on a really bright start, I am seeing a (photographic term ahead) 4 point star filter effect, i.e. there are 4 rays that spread out in 4 directions from the bring element accross the entire FOV. Is this normal? Or did I get a bad eyepiece?

    Thanks for any response.
    You should also be seeing the diffraction spikes at low power.

 

 

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