On telescopes, all of the optical pieces need to be aligned. Whether it is a mirror or lens, if they’re not pointing in the right direction the image will suffer. A Newtonian reflector has two mirrors and they must be aligned to each other and the focuser. There are a number of tools that can be used to accomplish this. One of them is the “laser collimator.” This device sits in the focuser like an eyepiece and shoots a laser out of the front of it. The laser beam is reflected by the secondary mirror towards the primary mirror. The secondary mirror is then adjusted until the laser strikes the exact center of the primary mirror. Some laser collimator have a cutout with a screen built into them allowing the return beam from the primary mirror to be seen. The primary mirror can be adjusted using the return beam.
All of this is a waste of time if your laser collimator not collimated. Ideally, the laser should be emitted so that it is perfectly parallel to the body of the collimator. If for some reason it is not, it must be fixed before it can be used. I manged to pick up an Orion brand “Deluxe Laser Collimator” for cheap because it was out of collimation. To fix it required some minor adjustments. Here’s the steps I took to fix it.
The easiest way to check the alignment of the laser with respect to the body of the collimator is to spin it. If the laser is not aligned to the body and the collimator is spun about the axis the laser should be on the laser beam will trace out a circle on a surface in front of it. The further away the collimator is from the surface, the larger the circle will be.
To hold the collimator, I made a set of V blocks out of wood. First, I ripped a V into a piece of 2×4 and cut it into pieces.
Next, I made a spacer block large enough to fit the central bulge of the collimator.
I attached it all to a base that I could use to clamp the block down to a fixed surface.
The laser emitter inside of the collimator is pointed via three set screws. These set screws require a 2mm Allen wrench to be adjusted. These set screws can be found under the label sticker on this collimator which should be removed during the procedure. (Aside: The set screws are under the label on the regular Orion laser collimator too.) The set screws are located in the little holes in the body. Mine had some kind of RTV in the holes that had to be scraped away first.
The collimator was then placed into the V blocks and pressed against the front block to check the alignment.
On a wall across my living room, I put up a sheet of paper and marked out the circle traced by the laser.
Now the set screws are adjusted and the collimator is rotated to check the of the size circle it creates. This is repeated over and over again until no movement in the spot can be noticed. At this point, I marked where the laser point hit the paper to use as my new reference point. As before you’ll iteratively adjust and check. But now, since the movement is so small, you have to walk back and forth between the paper and collimator to see how the spot has moved. Note that the set screws seem to push on some springs inside of the collimator which means you don’t have to turn one set screw in and reverse the other two at the same time.
Once the spot doesn’t move anymore when you rotate the collimator you’re finally ready to use it on the scope. Once the scope is collimated correctly, the return laser spot should fall in the hole in the middle of the collimator. This is the most accuracy the stock collimator can give and you’ll need to use different tools to improve upon the collimation.
Now to go look at Jupiter!