Astrophotography Telescopes

Galileo & Newton: Two Men, Two Telescopes

Astrophotography telescopes are available today thanks to two great scientists. The first was Galileo Galilei who invented the refractor telescope about 400 years ago using a lens at one end and an eye-piece at the other. This design is still in use today and is popular with beginners.

A good starter telescope in this range is 60-90mm on an alt-azimuth mount (meaning it moves up and down (altitude) and side to side (azimuth)). Refractor telescopes in this size-range are inexpensive but will bring out good detail on the Moon. Larger refractors can be problematic and false colour can occur, known as 'chromatic aberration'. A good choice, if you're looking for an inexpensive way to get started in astrophotography. Amazon have a good range of refractor telescopes many under $100 and starting from as little as $25.49.

Below right: Orion ShortTube 80 Equatorial Refractor Telescope

The development of astrophotography telescopes took a new turn when Sir Isaac Newton invented the reflector telescope which uses mirrors instead of lenses to gather light. Although considered better than refractors as they offer more light-gathering power per dollar, there are a couple of drawbacks.

Firstly, they have to be cooled down to match the temperature of the night air before they can be used; patience is required! And secondly, they have to be re-aligned from time to time. Amazon's reflector telescopes also start at well under $100.

Technical Advances

In the 1960s, an amateur astronomer called John Dobson invented a telescope with a large objective diameter (for greater light-gathering power) combined with portability for travelling so he could set up in places where light pollution was absent. He used simple and inexpensive components in a design which is used today for a whole range of wide-aperture reflectors.

John Dobson's design is ideal for observing dim, deep-sky objects, particularly as it has a large aperture, and because Dobosnian telescopes are made of light-weight materials. Dobsonian reflector telescopes up to eight- or ten-inch aperture can be handled easily by one person while being large enough to show hundreds of galaxies and resolve globular clusters into thousands of individual stars.

Right: Orion SkyQuest XT10i Computerized IntelliScope Dobsonian Telescope with Object Locator

Dobsonian mounts support a telescope in the same way a canon is mounted. However, there is another method known as an equatorial mount (sometimes called German Equatorial Mount) which uses counterweights to balance the telescope. This type of mount lets you track stars and planets with a slow-motion knob or with a motor drive. Good equatorial mounts are more expensive but will keep celestial objects centered in the eyepiece - essential for astrophotography. Follow the link to find out more about German equatorial mount telescopes.

Putting it all Together

Catadioptric telescopes use a combination of mirrors and lenses to effectively 'fold' the optical path into a shorter tube making them very light weight. This modern design works well with computerized mounts enabling you to easily find stars, galaxies and nebulae.

The only drawback is the high battery consumption so you need to use rechargeable batteries unless you have it plugged in to the mains or your car cigarette-lighter. Catadioptric telescopes are a good buy as they combine power with portability. To see the Amazon's best-selling catadioptric telescopes, click the link - updated hourly.

My Advice for Beginning Astrophotographers

Right: Celestron NexStar 4 SE Telescope

If you want to make photographs with your telescope, my advice is to purchase the one with the largest aperture you can afford and preferably with a computerised 'goto' function for simplicity of use. There are two types of computer control, one where you move the telescope until the attached hand-controller says you are on target and the other which has a motor-drive that does all the work.

Also beware of manufacturers who claim 500 times magnification for small telescopes - anything at that magnification will be fuzzy. The maximum useful magnification is roughly 50 times the aperture in inches or twice the aperture in millimeters.

Finally... a T-adapter and a T-ring are required to mount a camera on astrophotography telescopes.

T-adapters allow you to attach your 35 mm SLR camera to the prime focus of your telescope. This arrangement is used for terrestrial photography and short exposure lunar and planetary photography. It can also be used for long exposure deep-sky photography.

T-ringsconvert the camera's mount to a standard T-thread, allowing you to couple the body of your camera to a camera adapter or, in some cases, directly to the focuser of a telescope.

Oh, and a final, final bit of advice concerning eyepieces. A good eypiece is one of the most important parts of your telescope but don't buy zoom eyepieces as the only good ones are really expensive - around several hundred dollars! To enhance magnification of your eyepiece, you can attach a Barlow Lens which will double, triple or quadruple the magnification.

Follow this link to read my quick-start guide for beginning astrophotography or this link if you want to start making great shots of the moon.