From the elementary grade amateur to the tenured professional astronomer who decides to buy one, is buying your own astronomical telescope still a good investment?
By: Vanessa Uy
For the tenured professional whose significant other is understanding enough to allow him or her to own a “reasonably-sized” astronomy telescope – given that the one he or she uses on the job probably has a primary mirror taller than their two-story house. Owning a “portable” astronomy telescope surely has it’s own advantages. For the elementary grade amateur – or those in between – there’s nothing more satisfying than emulating the Golden Age of 17th Century Astronomy every time you use your telescope. But if you are looking for one, read on. Given that 2009 has been designated as the International Year of Astronomy, everyone should have the opportunity to experience first hand of using your very own astronomical telescope.
Even though there are very user-friendly astronomical telescopes that cost around 3,000 US dollars though the wisdom of shelling out with that sum of money can be questionable - especially if your funds doesn’t stretch that far. We should be looking for something more modest given that the world is currently in a recession. The second hand classifieds selling such items – like those on major astronomy magazines like Astronomy or Sky & Telescope - can be a good place to check out. But there are those brand-new priced between 150 to 500 US dollars that will do very well as starter telescopes. Even the ubiquitous 10 X 50 binocular telescope qualify as a very good starter refracting astronomical telescope. It can be used to see the major craters on the Moon and even has the magnifying power to see the planet Uranus.
There are two basic kinds of astronomical telescopes that you can choose: refractors and reflectors. A telescope’s primary function is to collect light and gather it to a focus. A refractor telescope uses a lens – called the objective lens – to refract or bend light to a focus. While a reflecting telescope uses a mirror – called the primary mirror – to reflect light to a focus. To know which type of astronomical telescope is best for you very much depends on what you will be looking at most of the time – or your specialty. Refractors are generally better for viewing small bright objects, like the Moon – if you consider the full Moon “small” – the planets, and double stars. Reflectors are generally suited for viewing large dim objects like the Milky Way, nebulae, other galaxies and star clusters.
When those in the know talk about a telescope’s “size” they are talking about its aperture. Aperture is the diameter of the telescope’s primary lens or mirror. For example, a 4-inch reflector doesn’t mean that the telescope is 4 inches long. It means that its primary mirror is 4 inches in diameter. For some weird reason, the aperture measurement of refractors or lens telescopes are usually given in millimeters, while the apertures of reflecting or mirror-type telescopes are usually given in inches. And remember an astronomical telescope’s job is to collect light. The larger the aperture, the more light it collects and the sharper the image it delivers. So chose the largest one you can afford because more than anything else, aperture determines what you will be able to see with the telescope.
Vibration can be an issue when it comes to starter astronomical telescopes. No matter which kind of telescope you choose, make sure it is attached to a good, sturdy mount. Telescopes mounted on long skinny legs that are held together with tiny screws are not worth the time and money. There is nothing worse than trying to use a telescope that makes the planet Jupiter look like that alien probe in the sci-fi TV series Threshold every time the cat walks by. Astronomical telescopes – especially the reflecting type – are prone to vibration. Even though my trusty but rusty Celestron 8-incher probably cost 1,500 US dollars when new, I can’t even play my stereo at a decent enough volume every time I use it because it vibrates wildly in time to the music. So listening to J.S. Bach’s organ cantatas or Iron Maiden’s Fear of the Dark while using a reflecting astronomical telescope is out of the question.
Speaking of astronomical telescope mounts, most beginners’ telescopes come with a simple alt-azimuth or equatorial mount. The “alt” means altitude and “azimuth” refers to horizontal movement. Which means an alt-azimuth mount allows the telescope to be moved or aimed up and down of left and right. An equatorial mount is set up so that one axis always points to the North Star. This type of mount moves in curves that match the movement of the celestial bodies in the night sky. Which can be an advantage if you want to use your telescope to capture long exposure photographs of a dim star using de rigueur 150 ASA 35mm photographic film.
There are advantages and disadvantages of each type of mount. Alt-azimuth mounts are mostly used in refractor or lens-type telescopes and are easier to use. And can be a boon if your telescope does double duty as a sniper’s spotting telescope. Especially if you are skilled enough to be a able to hit a bowling pin from 6,000 feet away using a rifle that fires the .50 caliber Browning Machine Gun cartridge. Although equatorial mounts – usually relegated to reflecting astronomical telescopes - are primarily designed to track celestial objects with ease. Plus the latitude and altitude readout on the equatorial mount can be very educational, especially if a seasoned astronomer ask you about the coordinates of the particular patch of night sky you are currently looking at. But most of all, it doesn’t matter which kind of mount you get, as long as it is sturdy enough for your telescope not to vibrate wildly every time the cat walks by.
By now, you’re probably asking how much magnification capability can I buy for my money. Sure enough, commercially manufactured astronomical telescopes’ power specification can be a contentious issue, especially since entry-level manufacturers tend to be too optimistic – even dubious - about the capabilities of their product lines. A telescope by itself doesn’t magnify anything because it doesn’t make objects look bigger it makes objects look brighter.
Making things look bigger is the job of the eyepieces you use with the telescope. Which – to the astronomical telescope’s manufacturers’ disdain – can allow you to use microscope magnification eyepieces as magnification eyepieces for your starter astronomical telescope. So it can be a boon if you also own a starter microscope. By changing eyepieces, you change the magnification. In most cases, the eyepiece will be marked with a number – usually in millimeters – that tells its focal length. The same eyepiece will deliver different magnifications in different telescopes. But in general, the lower the number on the eyepiece, the higher the magnification it delivers.
And believe it or not, you don’t even need a lot of magnification to see some interesting celestial vista. You can see Jupiter and the planet’s four biggest moons at a magnification of just 15 times (15X) – which is half that of the magnifying power of Galileo’s first astronomical telescope. While Saturn’s rings pop out at around 30X magnification. It is worth noting that most beginners’ astronomical telescopes – especially those with small apertures – can’t deliver a good image of anything at much over 150x. Either the result is an image that is too dark, since higher magnifications tend to darken the image, or is an overly distorted mush. Most entry-level astronomical telescopes – those priced between 150 to 300 US dollars – come with one or more eyepieces. You can also buy extra eyepieces separately or use ones from your microscope. Generally, it’s nice to have three sets of eyepieces: one for low power around 15X, one for medium power around 30X to 60X, and one for high power around 100X or greater.
For those beginners looking for an astronomical telescope on the cheap – which usually means second hand – avoid falling into the “long skinny trap”. I mean don’t discount a telescope just because it doesn’t looks like your typical astronomy telescope – i.e. long and skinny and mounted on a tripod. I’ve frequently encountered second-hand telescopes being offered on garage sales and swap meets that although very good, tend to look weird. Like the Astrocan, a round telescope that rotates on a short metal base. And Dobsonian reflectors – featured in the movie Roxanne – which have very stable box-shaped alt-azimuth mounts are often featured on Internet adverts being offered at prices too low to ignore. These two types are probably the most common second-hand astronomical telescopes being offered for sale. Although these types of astronomical telescopes have the disadvantage of not being so man-portable, unless of course your observation spot is accessible by car.
A good place to buy an astronomical telescope if you chose to buy one brand new are astronomy specialists shops – although some offer second-hand and “ex-dem” models at “very reasonable” prices. The clerks are more than likely to be able to help you choose a good scope within your budget, and you’ll also be able to test the telescope at the store. Also, you will be able to take the telescope back to the store if there are manufacturing defects. Or servicing within the warranty period since the shop is probably the telescope manufacturers authorized distributor / dealer. And the specialist shop carries a line of eyepieces and other accessories that you may want to buy later on. And believe it or not, specialist astronomy shops are probably the last place on the planet that sells 35mm photographic film. Given that - to my knowledge - everyday picture taking / photography has more-or-less gone completely digital since 2005.