So you’re going to build a telescope?

So you’re going to build a telescope?


Is that hard?

Maybe? But the internet tells me it’s doable.

How long will it take?

Several months if I put in a lot of time each week.

Will you save money by building instead of buying?


So why are you building a telescope?

For the LOLz?

This has been a fairly typical conversation since deciding to make a telescope, and it is often punctuated with a look of doubt. Amazingly it is actually something that can be achieved by an amateur with only some basic tools, a bit of theory and a lot of patience. My first exposure to telescope making was in an astronomy club as a teenager (the Kingston branch of the Royal Astronomical Society of Canada). Although I didn’t make a telescope myself, other members produced many high quality telescopes that I had the chance to use. Without having seen the functioning product of amateur telescope making I’m sure I would have been dubious as well.


One thing to clarify is what type of telescope I’ll be making. And to do that requires a quick description of how telescopes work. What can be seen with the naked eye is limited by the size of the pupil and how much light can enter the eye. To see fainter objects, or magnify distant objects requires more light. The advantage of a telescope is that it collects light from a much wider area, and then focuses it down to a point just in front of your eye. So an 8 inch telescope essentially gives you an 8 inch wide eye!


To collect and focus that extra light can be done in different ways. The long tube telescope that most people picture is called a refractor, and uses a lens to bend light to a single point. The type that I’ll be building is called a reflector, and uses a concave mirror to bounce light back up towards a single point. The result of both is the same: take light from a large area and focus it down to a small point that can be viewed by a human eye.

A telescope is defined by the type of optic it uses (mirror or lens) and the diameter of that optic. The Pyrex disc that I’ll make my mirror out of is 8½ inches and therefore the finished telescope will be an 8½ reflector. In this way telescopes can be compared, and the cost of a similar 8 inch refractor is about £300. Even though I’ll likely end up spending more than this to make my own it’s a target that I’ll aim for. As telescope optics get larger the cost to purchase finished telescope increases much faster than the cost to build one. So although it may cost me more to make this first telescope I could save hundreds or thousands of pounds if I want to build a larger telescope in the future.


But for me this isn’t about saving money, it’s about gaining a better understanding of how telescopes work, and (hopefully!) the satisfaction of building a precise scientific instrument from scratch. I now have all the supplies I need to make my mirror, and so all that’s left  is to get started!


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