Flintstone Stargazing

September 1, 2007

Aligning, cleaning and collimating

Filed under: astronomy, Clouds, Equipment — Ed @ 5:56 pm

Since the weather lately has looked like this:
Afternoon Sky 9/1/07
and the plants have looked like this:
Water on a canna lily leaf
I have not been able to add any new photos to the site (or really do any viewing at all). Of course, we’ve badly needed the rain for a long time so I’m not really complaining too much. After all, my lawn’s looking better. 🙂

Since I haven’t been able to do any viewing, I decided to field-strip my telescope and document it here on my site. A couple weeks back, I collimated my telescope using these instructions that I got when I bought my collimater. At that time, I pretty much skipped the first several instructions for lack of time and used just the collimation instructions, not the instructions for alignment prior to collimation.

Beyond issues with focusing that I’ve been having, I also believed that some of the chromatic aberration and other issues might be from bad alignment. I also figured it’s always good to have clean mirrors; I could see from the other end of the tube that at least the primary mirror was smudged and a bit dirty. What I didn’t realize was how dirty the secondary mirror was.

Here’s how I did it:

First, I unmounted the telescope and gathered the tools I would need:
The tools for aligning my telescope

Next, I unscrewed the primary mirror “cartridge” (for lack of a better term):
Unscrewing the mirror

And I carefully removed it from the telescope. Here’s what it looks like (note how dirty and smudged it is):
My primary mirror right after I removed it from the telescope

Next, I took my lens cleaning kit including a microfiber lens cloth and lens cleaner and cleaned the primary mirror. Important Note: I have read that you should not use anything except air (a blower bulb or compressed air) or (if you are really careful) water to clean a mirror. This is because wiping anything on the mirror can remove some of the reflective aluminum coating and eventually can require you to re-coat your mirror, which can be expensive. This telescope was inexpensive and the mirror was really not very clean so I chose to wipe it carefully. Use a cloth at your own risk.
Cleaning the primary mirror of my telescope

After cleaning, I measured the primary mirror. While supposedly it is a 114mm primary mirror, I found that in reality it is only a 113mm primary mirror! I smell a class action lawsuit in the making. Okay, that’s not a big deal, but in order to find the center of the mirror, I needed to know what the diameter was so I could divide it by two. I then took the compass and set it to 56.5mm:
Measuring the middle

I marked the middle of the mirror and then placed a paper-reinforcing ring around the center, as the instructions mentioned earlier directed me:
A reinforcing ring on the primary mirror
(note how much cleaner the mirror is – the small lines in the center of the reinforcing ring are where I marked the center using the compass)

Finally, I replaced the “cartridge” and screwed it back into the telescope body. Then I followed the instructions for alignment and collimation. While aligning, I found that the secondary mirror (the small angled one near the top of the telescope) was aligned off-center. I also noticed how dirty it was. I cleaned it off and adjusted it using the small screws on top so that it was now properly aligned with the center of the primary mirror. Finally, I collimated the telescope using my handy-dandy laser collimater.

I hope this will make a difference in the quality of viewing and photography that I hope to do as soon as the skies clear up.


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