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Owner's Manual Collimation Section http://webstertelescopes.com/forum/viewtopic.php?f=7&t=593 |
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Author: | Eric [ Thu Apr 14, 2011 7:08 pm ] |
Post subject: | Owner's Manual Collimation Section |
I want to thank all of you who sent in pictures and ideas on the collimation section of the new Owner's Manual. I've distilled all of the information and am posting the rough draft here. The number one problem that everyone complains about is that collimation directions have too much theory, and too many unclear diagrams that do not show the actual view of what you see when you look through the Sight Tube. We took the time to set up a camera tripod and shoot the actual views that you will see when you collimate yourself. Please take a minute to read it over and comment before it goes to press. Thank you! |
Author: | Eric [ Thu Apr 14, 2011 7:18 pm ] | ||
Post subject: | Re: Owner's Manual Collimation Section | ||
Centering the Secondary holder is the first step to collimation. This is a good "kitchen table" project that only has to be done maybe once a year. You will be much more comfortable when seated at the table than you would standing in the garage. Start by putting down a light colored towel on the table and placing the UTA (Upper Tube Assembly) upon it. The light color will reflect some light up onto the secondary mirror and make the mirror very easy to see against the black cowl of the secondary holder. Tape a white piece of paper to the UTA directly across from the focuser. The paper will give us a high contrast background that will make the otherwise flat black parts stand out from each other.
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Author: | Eric [ Thu Apr 14, 2011 7:29 pm ] | ||
Post subject: | Re: Owner's Manual Collimation Section | ||
Looking through the empty focuser from a few feet back will quickly determine if the Secondary Holder is way out of line. Here in this example we see that the Secondary holder is much too low.
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Author: | Eric [ Thu Apr 14, 2011 7:32 pm ] | ||
Post subject: | Re: Owner's Manual Collimation Section | ||
Here we see that the Secondary Holder has been raised and is now roughly centered in the empty Focuser. We adjust the height of the holder with the 9/16" nut on the top of the Secondary Stalk. Make the adjustment, but do not tighten the nut very tight yet.
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Author: | Eric [ Thu Apr 14, 2011 7:33 pm ] | ||
Post subject: | Re: Owner's Manual Collimation Section | ||
Insert a Sight Tube into the focuser. We use and recommend the CatsEye 2" Sight Tube, so that is what is pictured here. The Sight Tube has a telescoping inner tube allowing it to be customized to any focal ratio. Set this now if you have not done this already. While looking through the Sight Tube, roughly adjust it by moving it in and out through the focuser until you have all of the secondary mirror AND some of the Secondary Holder Cowl in view. Tighten the thumbscrew on the Focuser Drawtube to lock it in place.
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Author: | Eric [ Thu Apr 14, 2011 7:36 pm ] | ||
Post subject: | Re: Owner's Manual Collimation Section | ||
Looking through the Sight Tube, here we see that the Sight Tube needs to be backed out further, because we can't see the Secondary Holder Cowl all the way around in the view. Turn the Focuser knob to move the Sight Tube towards you.
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Author: | Eric [ Thu Apr 14, 2011 7:42 pm ] | ||
Post subject: | Re: Owner's Manual Collimation Section | ||
Here we have backed out the Sight Tube so that the Cowl is visible all the way around the Secondary Mirror. But, we still see some of that white background paper! This most likely tells us that the entire Secondary Mirror Holder needs to be rotated (in this example, clockwise). Rotate the Holder while looking though the Sight Tube.
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Author: | Eric [ Thu Apr 14, 2011 7:59 pm ] | ||
Post subject: | Re: Owner's Manual Collimation Section | ||
Here, we have rotated the Secondary Holder and have a nice, even Cowl visible all the way around the edge. None of the white background paper is visible. This is a pretty good result. Why only pretty good? If we really look close, there is slightly more Cowl showing at the 4-5 o'clock position in the view, than in the 10-11 o'clock position. To fix that we use the leveler screws on the focuser base. Of course this is being picky, but tweaking things like this is 1/2 of the fun of owning a telescope. This is exacting work, so you will want to be seated. While looking through it, you can push the Sight Tube slightly in any direction and get the idea of which leveler to turn. Let the leveler screw "bite" into the wood Focuser Board a little bit. If you need more than a single turn to make it perfect, you may want to loosen the mounting screws for the Focuser itself. A single turn is as close to a hard and fast rule as we have. You will quickly get a feel for the adjustment, and again, you usually only have to do it once a year.
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Author: | lightyear [ Thu Apr 14, 2011 10:50 pm ] |
Post subject: | Re: Owner's Manual Collimation Section |
Looking really good so far. Easy to understand, visualize, and not overly complicated. Not intimidating for newbies. -David. |
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