How to Make a Collimation Cap
Do I Need to Collimate My Telescope?
We've talked at great length about the different types of telescopes and their benefits. As we've said before, each type of telescope has its merits and demerits. When it comes to the topic of collimation, the benefit of a refractor is that the way the lenses get mounted into the telescope tube, there is much less chance of movement under the conditions of normal use.
But when you're dealing with catadioptrics and plain old reflector telescopes, there's no denying their benefits. They're really effective, and their simple configuration often means they're less expensive than some of the other options.
While a lot of things about reflectors can't be beat, there's still one thing that can be a bit of a pain: reflectors need to be collimated.
Because of the way most mirrors are placed in the telescope tube, it's a lot more likely that they'll move around over time and with use. This can result in a troublesome misalignment that saps effectiveness and reduces image clarity.
To put the mirrors back into alignment and get your telescope back to working, it needs to be collimated. Collimation is the process by which the light path of the telescope is correctly re-aligned. While collimation isn't that difficult, the prospect of adding another level of technical expertise required for the use of a telescope actually has turned a lot of beginners and amateur astronomers off of reflectors, which is a shame. With a little bit of know-how (and the right tools, collimation doesn't have to be a daunting task).
What's the Cheapest Way to Collimate a Telescope?
There are several ways to successfully collimate a telescope, but the cheapest way is to build a home-made collimation cap. These home made focuser caps can be made with a minimal number of tools and items.
While it's not the easiest way, it's a really attractive option.
Before we start, let's get one thing out of the way: this is absolutely an effective way to collimate a telescope, but it's not the most precise. For that, we would point you to some of the other collimation tools on the market.
That having been said, here's how to build your own home-made collimation cap.
What is a Collimation Cap?
First off, we recommend allocating some time to this. Don't expect to knock this out in a few minutes and then move on to observing with your well-collimated telescope. To do the best job of this, it's important to do it carefully.
A collimation cap is a sort of dummy eyepiece with a dead-center hole that lets you line up your mirrors. Because it works simply by being on center, it's easy to create your own collimation cap using things you probably already have lying around the house.
This video (no sound to speak of) has an example of a collimation cap, in case you're having trouble picturing it.
A lot of people ask what's the best size hole for a collimation cap, and the truth is that the size of the hole doesn't really matter. A good rule of thumb is about 5-7 mm, but it doesn't need to be exact. You probably don't want to drill a gigantic hole, as this could mess with your precision. But what matters is that it's in the middle.
How to Make a Home Made Collmation Cap
To build a collimation cap, you have a couple of options when it comes to materials.
A lot of people opt to just use the cap that covers their eyepiece. The benefit of this method is that you don't have to have any additional pieces; you've already got your cap right there. Of course, the problem with using the eyepiece cover to make a collimation cap is that you now have a hole in your eyepiece cover, which means you've exposed your eyepiece that much more to dust. It's not a major problem, but it is something to keep in mind.
Another option is to use a film canister. Those black plastic little canisters that hold rolls of film do a great job, but in these days of digital cameras they might be a little more difficult to find. If you're going to use a canister, the only additional step is to cut off the bottom. Be careful to cut it flush, as an uneven cut can introduce error into the subsequent collimation alignment.
Whatever you're using, the next step is to drill a small hole in whatever you're using. You can do this with a small drill bit, or in a pinch you can eve use the point of an ordinary pair of scissors. As mentioned above, this need only be a small hole, but make sure it's dead center.
Lots of people have different ways of making sure that hole is in the exact center, but we've found the easiest way is to use a piece of paper or card stock. Trace the edge of your canister or eyepiece cap onto the paper and carefully cut it out, making sure that your cut-out aligns perfectly. Next, fold the paper cut-out North-South and East-West, and then unfold. Where those lines intersect should correspond to the middle.
Tape your paper cut-out onto your cap (or the cap of the canister), being extremely careful that everything is lined up, then drill at the center point.
Make sure the hole is clean. Get rid of any hanging bits of plastic.
That's it. You're now ready to collimate your telescope using your homemade collimation cap.
Once you've created your own collimation tool, head on over to our article on collimating your telescope. Once you're all aligned, you can get back out there with clear eyes (and mirrors and lenses) to see all the things you're looking for.