Collimating a refractor without some real method of aligning the optical
path can cause a severe case of frustration. I have a 5" Meade EDapo also,
and was really not very happy with the focuser mechanism. There is no way,
short of trying to tighten the tube mounting screws, to adjust the angle of
the focuser tube. I know this may sound like a lot of work, but here is what
I did to achieve the ability to separate 1" double stars, and see very near
perfect diffraction rings.
I first used a laser collimator in the scope using a piece of paper over
the end of the tube with a center dot on it to verify that I had a problem.
The spot at the objective was about 1/4 inch from being centered. Obviously
I had a focuser problem. I removed the focuser from the tube and removed the
poly- ethylene slides that align the focuser tube in the housing. This
leaves a small amount of clearance inside the tube. I removed the same poly
slide from the aluminum bar that doubles as the focuser lock. these were
replaced with six screws with poly-ethylene tips to ride against the tube.
This makes the focuser tube adjustable like a finder scope. The laser
collimator was then reinserted and the focuser tube adjusted until the dot
was Exactly centered on the objective. The reflection can then be observed
through the objective end. It should reflect back on the laser collimator
centered. Be sure not to allow the laser to shine in your eye. I put 2
pieces of electrical tape across the center of the tube ( not the lens of
course ) for the laser to shine on instead of my eye. There are actually 3
reflections that return to the back of the tube. The objective can now be
adjusted so that the reflections are as centered as possible on the
collimator. Be careful not to over tighten the objective adjusting screws.
If you don't want to work on your focuser as I did, then just shim the laser
collimator until the dot is centered. My objective was out of adjustment
such that the reflections did not hit the collimator at all, so this method
helped me quite a bit. Tom

At 01:07 PM 4/1/98 -0500, you wrote:
>Anyone have a good procedure to follow to collimate a refractor (5"
>Meade APO)?
>
>I have Meade's procedure and it is pretty useless. It is based on
>creating a mask over the focuser with two holes in it at equal distance
>and in a line, with both on one side of the center of the mask. Then,
>with the lens cap on, install the mask over the focuser and shine a
>flashlight thru the hole in the mask closest to the edge and look thru
>the other hole, look for the image of three points of light reflecting
>back off the lens cap and adjust the appropriate lens cell adjustment
>screws to get the points of light to line up with the two holes in the
>mask. You do this procedure in two axisis, horizontal and vertical.
>After I did this, I had to really adjust it to get alignment in both
>axis, and the resultant star test images got a lot worse with the
>"comet" effect then I previously had. Meade then changed their mind and
>said to do the procedure in the vertical axis only (in line with the
>focuser rack) and forget about the other axis. Didn't sound right, but I
>tried it, still no joy.
>
>I have now put the cell adjustment as close to where it originally was
>as I can get, but I am still getting some of the characteristic "comet"
>effect with the stars that is indicative of off-collimation for a
>refractor.
>
>BTW, several star tests were done previously, diffraction rings were
>clearer on one side of focus then the other. Very slight off center of
>center rings, very difficult to see. Ronchi done at 120 and 150
>lines/inch with no anomalies, looked real good. It is very difficult to
>see the off center of the difraction rings
>
>Here is my game plan for collimating this thing. Set the scope up, get
>it in ggod focus on a good Mag 2 or 3 star at about 120X and just adjust
>the screws until I can get the comet effect to disappear. Then go to
>200x or greater and repeat. I think seeing the off-center of the
>diffraction rings is too difficult and precludes doing this out of
>focus. The comet tail is much easier to see.
>
>Any coments??? Anyone have a better procedure, short of sending it down
>to company 7? Also, if I do it my way, how should I shift the cell in
>relation to the direction the comet tail is pointing, should I move the
>cell in or out in that quadrant?
>
>Thanks for any help!
>m.
>
>
>
>
>
TRC

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