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  1. #1
    aonifer's Avatar
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    Default Cheshire eyepiece / combination tube



    Hi guys,

    I recently pulled out my old Orion Deep Space Explorer (6") for the first time since the 90s. After a decade+ of cross-country moves and such, I've found I needed to recollimate the mirrors. after reading various sites, I decided to build my own Cheshire eyepiece. I found a random plumbing coupler at Lowe's for about a buck, which has the advantage of having an octagonal "bolt" section, and made aligning the dental-floss crosshairs really easy.

    My main problem is that I had only a Dremel to cut the 45-degree angles for the reflector. My question is, how accurate does that angle have to be? Is it only to get light down to the primary, or is there something to the alignment I'm missing? It seems like collimation is mostly a matter of aligning the crosshairs and reflections of crosshairs with the central ring on my primary (I think I got the crosshairs right, because when I spin the eyepiece in the focuser, the center doesn't seem to move).

    Also, another problem is that when I look through the eyepiece, the secondary looks circular, but part of it is cut off. I'm not even sure what adjustment needs to be made to fix that. I have one of those dreaded single-stalk secondary holders. It seems like I need to move the secondary (or the focuser) towards or away from the primary.

  2. #2
    mplanet62's Avatar
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    Default

    Hi,
    And Welcome to Forum!
    Cheshire reflector does not have to be precise - viewing hole and cross-hair need to be centered really well. Reflector's purpose is just to bring some light inside the tube and make a nice round "target" to coincide with primary center mark. Do not worry about the secondary for now - as long as you can see the whole primary reflection in it with any focuser extension. If not - you need to adjust it lengthwise. Done by loosening three radial screws on secondary holder and rotating the center one. Do in in horizontal position only to avoid dropping stuff on your primary.
    Last edited by mplanet62; 11-06-2011 at 12:32 PM.

  3. #3
    aonifer's Avatar
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    Default

    Excellent! Thanks. My concern with the secondary is that it's just a single stalk attached to the focuser, so to adjust anything more than the distance to/from the focuser and one axis of tilt requires bending the stalk.

    I wasn't able to do anything today, but I took it out last night and did some basic tests, and it seemed to perform well.

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    Default

    Welcome to the forum. If you could post a picture of the piece you made, I would be very interested in seeing how you made it.

    Tom

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    Zhumell Z12; GSO 6" Imaging Newtonian; Jason 10X50 binoculars;


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  5. #5
    aonifer's Avatar
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    Default

    I'm still fiddling with it. I can't post URLs, yet, but if you Google "homemade combination tube", the first link is where I got the idea. The tube is some random coupler I got from the plumbing section of Lowe's. It's the only thing I actually paid for. The reflector and the "cap" are from an old disposable pie pan I had for some reason, and the crosshairs are dental floss. I need to replace the cap with something I can center better. I also had to shave down the threads on the crosshair end, which is probably my other big error as far as centering. Obviously, I'm still working on the reflector, which is why it's just taped on for now.

    I also included a picture of the secondary mount, so you can see what I'm dealing with. Hopefully someday I can get a real 3- or 4-vein holder.

    IMG_20111107_225703.jpg

    IMG_20111107_225649.jpg

    IMG_20111107_221640.jpg

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    Default

    Replacement for this secondary holder looks like another project in wait.

  7. #7
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    Default

    Ha! Just last night I replaced the stalk with a 3-vein spider. Collimation was way easier (though my Cheshire was kind of a bust -- I don't think I shaved down the threads symmetrically enough), and I saw the best views of Jupiter I think I've ever seen in this scope. I tried to find Uranus, but my skills are a bit rusty, and I think it's behind some trees, now. Unfortunately, despite some really good weather, I'm stuck in an area with lots of streetlights and trees, so I only have a small patch of sky to look at. I'm going to head out later to see what the Orion Nebula looks like after it clears my building.

 

 

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