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Thread: Celestron Luminos - Incompatible with Dobsonian?

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    Default Celestron Luminos - Incompatible with Dobsonian?



    All,
    Just had a great First Light last night with my new 10" Dobsonian. Had serious issues though with a Celestron Luminos 10mm EP. Basically I could not get it to resolve anything until I had Jerry rigged an extension and had the focuser almost fully extended (looked like an Atlas V rocket sticking out of the focuser) Also it would not function with a Barlow at all. Looking through the the EP gives a view of formless, nebulous fog. I have the Luminos 31mm also, but did not have the opportunity to try that one out.

    A buddy out watching too told me that the Luminos EPs are designer for SCTs and are not suitable for a Dob? Is there any truth to this? Was I just doing something wrong? Do you have any experience with these EPs on a reflector? Are all Wide Field EPs unsuitable for my scope?

    Still it was a lovely night. Luckily enough I had the EPs supplied with the scope, a 10mm and a 26mm. The 10mm was useless but the 26mm was fine, and as I said I was able to make the Luminos 10mm function by hook or by crook.

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    Default Re: Celestron Luminos - Incompatible with Dobsonian?

    Using the 10mm with a barlow might have been too much power for your scope depending on the seeing conditions. I'd be curious to know how the 31mm works with your scope and if you have a similar issue. There are definitely wide field EPs suitable for your scope, the Explore Scientific 82* EPs would work very well with your Dob, as would TeleVue EPs, but of course you'll pay quite a bit more for the TeleVue options.
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    Default Re: Celestron Luminos - Incompatible with Dobsonian?

    I'll update when I've tried out the 31mm. The thing is literally the size of a grapefruit and weighs 2lbs 11.3 oz. I've got some magnets to use to weight the mirror end, so getting the scope to balance should not be an issue. I'm just hoping it will function.
    Roger
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    Default Re: Celestron Luminos - Incompatible with Dobsonian?

    What telescope do you have and what objects were you observing? Most 10 inch Dobsonians are around 1200mm focal length. So with a 10mm eyepiece you were at 120x, which is moderate magnification. However, if your seeing/transparency conditions were poor, 120x might be too high. The Luminos is an 82 degree AFOV eyepiece which should work well with your Dobs. I'm not sure why you needed to extend your focuser to get a clearer image. I assume you didn't need to do that with the 10mm eyepiece that came with the scope (although you mentioned that that eyepiece didn't work well either)? Perhaps 120x just didn't work well that night?

    Without getting into too many collimation issues, does your secondary mirror look centered in your focuser when looking down the center of the focuser with the eyepiece removed? Can you see all three primary mirror clips in their reflection in the secondary mirror, when looking down the focuser?
    Woody

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    Default Re: Celestron Luminos - Incompatible with Dobsonian?

    Hi Woody,
    Thanks for your response. I have a Sky-Watcher 10" Dobsonian. 1200mm focal length.
    Bear with me, I'm new to astronomy and this is my first scope. Having reassembled the kit I realize that I wasn't using any extension, but was confused due to the length of the eyepiece apparatus with the 2"-1.25" adapter and the focuser being fully extended. The Luminos 10mm worked fine, beautifully in fact, although both Jupiter and M13 both came into focus at almost full extension of the focuser. What concerns me is that I was seeing no image when using the EP with the Luminos 2.5 x Barlow. I've attached a couple of pictures just to make sure everything was attached as it should have been.


    Many thanks.
    Attached Images Attached Images
    Roger
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    Default Re: Celestron Luminos - Incompatible with Dobsonian?

    Roger, everything looks ok in your picture. The fact that you were getting a good image with the Luminos 10mm alone suggests that when using it with the Barlow, your effective magnification was too high (240x) for your observing conditions. The Barlow-eyepiece combination decreases the focal length compared to the eyepiece alone, resulting in increased magnification. You need pretty good seeing conditions for 240x or higher. I often get blurry images around 250x unless the sky is exceptionally clear. Happy observing!
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    Default Re: Celestron Luminos - Incompatible with Dobsonian?

    Well, you have it assembled correctly. However, the 2.5x barlow and the 10mm eyepiece are resulting in an effective focal length of f/4.0 which is less than your scope's focal ratio of f/4.7.

    That combination will focus occasionally in excellent seeing conditions (very rare) on planets and the moon. (The moon is easy, you can almost focus a Coke bottle on the moon.)

    The maximum, usable magnification of any scope is attained with an eyepiece that is approximately equal to the focal ratio, and then only with good seeing conditions.

    Next time, try it on the moon.

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    Default Re: Celestron Luminos - Incompatible with Dobsonian?

    Quote Originally Posted by rogercorbett View Post
    Hi Woody,
    Thanks for your response. I have a Sky-Watcher 10" Dobsonian. 1200mm focal length.
    Bear with me, I'm new to astronomy and this is my first scope. Having reassembled the kit I realize that I wasn't using any extension, but was confused due to the length of the eyepiece apparatus with the 2"-1.25" adapter and the focuser being fully extended. The Luminos 10mm worked fine, beautifully in fact, although both Jupiter and M13 both came into focus at almost full extension of the focuser. What concerns me is that I was seeing no image when using the EP with the Luminos 2.5 x Barlow. I've attached a couple of pictures just to make sure everything was attached as it should have been.


    Many thanks.
    I have a skywatcher. When using 1.25" eyepieces, you need to remove the larger extension. That's only used for 2" eyepieces. It's one or the other, not both. The 1.25" adapter should go directly in the focuser.
    Rob

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    Default Re: Celestron Luminos - Incompatible with Dobsonian?

    Saying you got the 10mm to focus was puzzling me. I just had a thought. Is it possible you're not pulling the secondary up high enough when you extend the struts? There are two detents on the Skywatcher struts. When using it visually, you need to pull the secondary assembly up as far as it will go so the struts will not extend any further. I believe the first detent is to get a camera to come to focus. That would explain why you have to focus so far out when using a 10mm.
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    Default Re: Celestron Luminos - Incompatible with Dobsonian?

    I have the Luminos 15mm, and the Luminos 2.5x barlow. I'm able to get the 15mm to focus by itself, and with the barlow in my Z12 Dob.
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