Recently I added an extra page to this blog, a page about telescopes.
This is an easy way to indulge myself into what has been my favourite hobby for as long as I can remember….in fact, as long as I’ve loved photography, you could say.
During those days, many, many decades ago, money was very short and so my dreams of owning a telescope remained dreams, until I was working. My friend Marty who also happens to be on WordPress knows where I’m coming from with this!
So anyway, the most frequent questions whenever I mention a telescope are “What type of ‘scope do you have?”
In order to address that, we need to take a whirlwind lesson in the basics….I’ll try and keep the techie terminology to a bare minimum, don’t worry!
There are 3 main types of telescope design. They all do the same thing, that is they magnify distant images so that we can see them, but they do that slightly differently.
But first, why don’t we see the writing on a newspaper say, 500 yards away? The reason is that the newspaper does not cover much space on the back of your eye, the retina, and so you cannot read it.
If somehow you could magnify that newspaper to a larger size, so that it covered more of your retina, then you would be able to see it. Like with digicams….without magnification, the newspaper would appear as a small dot on the digicam sensor, but if magnified it would cover more of the sensor, and consequently be able to make a clearer image of it. That’s the best way I can think of to explain it without getting involved in resolutions, chromatic aberrations and what-nots!
So basically we need something that can collect as much information from the object we want to see, in this case as much light, and then we need to magnify that information, or that light so that we can make sense of it clearly.
What can do that? A telescope!
As we heard, there are 3 types….reflectors, refractors and a newer type, the Maksutov-Cassegrain.
A reflector telescope (also known as a Newtonian telescope, after Sir Isaac Newton, the English scientist) is the most simplest, and many say, the most effective type you can buy.
The way a reflecting telescope works is, as the name suggests, by reflecting the light from the object you want to look at, onto a concave mirror at the bottom of the ‘scope, where it is reflected back part way up the tube again, hitting another smaller mirror, which bends the light sideways into an eyepiece that allows you to view the object.
Advantages of a reflecting telescope
- much cheaper than other types
- less to go wrong
- absolutely suitable for looking at deep objects, like galaxies, etc
- the image you see will not have chromatic aberration (bands of colour, or fringing of rainbow colours around the image caused by mal-performing lens characteristics)
- in some cases but not all, reflecting ‘scopes need to have their mirrors “collimated” meaning realigned, after some time. But with advanced mirror design techniques, this has largely become unnecessary.
- because of that little mirror that reflects light back into your eyepiece, a little light that comes down from the object into the tube, is lost, as the 2nd mirror is in the way.
- not really a disadvantage, but some people don’t like the size of reflecting telescopes, as they are larger than refractors.
This is the original telescope design, as used by the astronomer Galileo way back in around 1600.
With this type, the light from your object hits a large lens at the front, travels down the tube just as in the case of the reflecting telescope, hits another lens (or a set of lenses), before being ready to be visible either straight out of the end, or via a 90 degree bend that channels the light upwards, so that you can peer down to view rather than look up at an awkward angle into the tube. Remember, the more additional eyepieces, lenses, bends etc you place in the path of the light, the more light you will lose from the object, making it less clearly visible.
Advantages of refracting telescope
- can produce better images of planets or moons, but again, this is debatable, as there are more lenses in this type than the reflecting type, so more light can be lost through the lenses
- can cost a little less than reflecting telescopes
- are generally slimmer and lighter than reflecting telescopes
- generally more expensive than other types due to the large lenses required
- many suffer from bad colour fringing around the object (chromatic aberration)
- not really suitable for viewing very distant stars and nebulae etc, as large light-collecting ability is needed for these types of objects (refractors with large apertures can be bought and offer very good light-collecting, but are very, very expensive indeed…a reflecting telescope with its ability to collect huge amounts of light falling on its mirror is he most widely used type for distant viewing)
This type of ‘scope was designed by a chap called Maksutov in Russia, in the 1940s.
His aim was to design a ‘scope with the advantages of the reflecting and refracting types in one unit…those advantages being minimum chromatic aberration (fringing), a short tube (as in a refractor), high magnifications and lower costs.
So a Maksutov telescope uses both lenses and mirrors to obtain its image for you. The light from the object hits a large lens (a concave lens, not a convex lens as in the refracting ‘scope) at the front of the tube, is passed down to a large mirror at the end of the tube, where it is reflected back up to another lens/mirror combination, and then finally bounced back down again into a tube that leads to the eyepiece which you look through.
Advantages of a Maksutov telescope
- Very short body
- virtually no chromatic aberration
- cheaper than a refractor, although this again is debatable
- still very much more expensive than a reflecting ‘scope…you can buy a reflector with a larger mirror and hence higher light-collecting ability, for the same money, than a Maksutov
- the large lens at the front of the tube, because of its size, needs to be kept at the right temperature before using the ‘scope, as otherwise it will not give a fine image due to minute fluctuations in its size due to temperature…a very big problem which has been addressed to some degree nowadays, but again at a cost!
So there we have it! Those are the 3 main groups of telescope. Which one you choose depends a lot on how much you are willing to pay, how much you are going to use it, where you are going to store it etc. I’ve found that it’s best to have a permanent home for a telescope, where you can just walk in and start looking through it, rather than having to take i out of a box, set it up etc, by which time the object you wanted to see has been obscured by a cloud or has moved, or a more likely thing in Vancouver anyways…it starts to rain!
I will be posting a larger selection of very good telescopes for you to consider in this blog very soon…meantime, take a look at one or two here