Next part in the Sheet Metal Scope Saga...
I created a jig for my laser collimator by sinking 4 screws into a board, clamping it to a table and placing the collimator in the "cradle" created by the 4 screws.
Picture 1: Jig for the Collimator
Picture 2: Place Laser in the Jig
With the laser in the jig, I taped a piece of paper to the wall about 10 feet away and penciled in a dot where the laser beam hit the paper. Then, I rotated the collimator a little bit and drew another dot. In this way, after about 10 dots, I could see the circle traced out by the collimator and see just how much the collimator was out of collimation. If was off by about 3 inches.
Picture 3: Dots on Paper as Laser is Rotated
To adjust the collimator, I cut away the label which was hiding the 3 "set" screws. These turned out to be 1/16" hex head screws and as luck would have it, I had this size of hex key.
Picture 4: Cut Away to Expose Adjustments
By tweaking the "set" screws with the hex key, I was able to reduce the circle traced out by the collimator to about 1/4 inch at 10 feet. I figured this was good enough being within 0.1 degrees of center.
Picture 5: Adjust Set Screws Until Laser is Centered
Next, I installed my secondary holder and vanes. Instead of using the clip, I put four dabs of silicone adhesive in the holder and pressed the secondary mirror into the holder. I figure this way, I can always use a razor to cut away the silicone and pop the mirror back out if need be, and I get the bonus of not having the clip in the light path.
I had to retract the mirror as far as possible toward the front of the 'scope to the limit of the holder. Even then, I was off by about 1/8 inch as judged by the sight tube. Next time, I should drill the holes for the vanes about 1/4~3/8 inches further up the tube away from the focuser hole. It's good enough for how, however.
Picture 6: Secondary is Installed
Next step, install the primary into its cell. Problem: this mirror is slightly larger in diameter and so sticks out past the diameter of the cell by about 1/8 inch. Problem 2: this mirror is slightly thicker than the clips will allow. Luckily I have room to re-drill the holes for the clips about 1/8 inch up on the holder to give me room enough to compensate for the thicker mirror. And also, the slightly larger diameter is not a problem as the clips have enough "play". However, for now, with the clip screws at a slight downward angle, they have just enough "bite" to hold the clips pretty well. However, the rubber pads are in direct contact with the mirror, which might be resulting in "pinched" optics. When I re-drill the holes, I'll make sure I can get a playing card in there between the pad and the mirror. But for now, it's good enough.
Picture 7: Primary in its Cell
Next step, slap the primary on the back of the OTA, screw in the screws, and collimate the secondary.
Picture 8: Collimate the Secondary
With enough fiddling and tweaking of the secondary screws, I got the laser beam to hit right on my center spot. Looking through the sight tube, the secondary looks nice and circular, however, like I mentioned earlier, it is shifted ever so slightly toward the primary but I have no room to back this up, so I'll just go with it.
Picture 9: Collimate the Secondary Complete
Now, I'm going to bite the bullet and build a dedicated collimation cap out of some paper plates. This is the mask for the barlowed laser so that I can see the shadow of the center spot to get rough collimation.
Picture 10: Building the Collimation Cap
Picture 11: Collimation Cap is Built
Now, I insert the cap into the focuser from within the OTA tube and turn on the laser. I put a pencil mark where the laser strikes the surface of the cap.
Picture 12: Mark Center of Collimation Cap
Next, I remove the collimation cap and cut a hole where I made the pencil mark. The barlowed laser light will eminate from this hole.
Picture 13: Cutout Center of Collimation Cap
Now, I'm ready to collimate the primary mirror.
Picture 14: Barlowed Laser for Collimation
The nice thing about this OTA is that it is only 24 inches long, so with a small screw driver, I can tweak the collimation screws in the back and view the movement of the center spot shadow in the front at the same time. With my long tube, I had to use a mirror, which was very cumbersome. After much tweaking of the primary collimation screws, I got the center hole of the center spot centered on the hole in the collimation cap.
Picture 15: Collimation Looks Good
Something is a little bit amiss here. The shadow of the center spot is not fully illuminated. I think the hole in the collimation cap is too small.
Now, I think I'm ready for First Light!!!