The Lake County Astronomical Society

Aperture Lust

Jack Kramer

When it comes to telescopes, aperture rules. Talk to other amateurs and you'll find that sooner or later a lust for more aperture afflicts all of us. But before you succumb, it's worthwhile gaining plenty of eyepiece time with your present scope. What have you accomplished with it? Have you observed from a dark site? It's amazing what even a small telescope can show under good skies. I've long felt that most amateurs never exhaust the capabilities of an 8-inch telescope - what could be called the mid-range of aperture. In fact, the late deep sky authority, Walter Scott Houston, stated: "It's difficult to imagine anyone viewing every object within reach of a 6" telescope." And telescope-making author Mel Bartels recommends: "An 8 to 10 inch scope will show you tens of thousands of objects with enough detail to discern their astrophysical meaning, and still not be so complicated and heavy to lug that it will gather dust on clear nights."

Sure, you'd get a better view with a larger instrument. If big aperture lust prevails, there's the "two sizes" rule that says you only get significant gains in what you can see if you go up two standard sizes from your present telescope. Two sizes would typically be 8 inches to 121/2 inches, or 10 inches to 14 inches. The most noticeable difference will be if you increase light gathering by a magnitude or more. But other factors enter the picture: telescope design, for example. Going from a 10-inch SCT to a 121/2-inch Newtonian nets you a 56% increase in light gathering; however, it also gives a wider field of view that will be an improvement for visual observing of deep sky objects. Consider that the laws of physics prevail; high-quality Newtonian optics will best an SCT in terms of image sharpness. Is astrophotography in your future? Then the SCT might be the answer for you after all. If you're adamant about sharp views of the planets, then an apochromatic refractor might be just the ticket.

So it can be awkward offering opinions to someone about buying a telescope because each of our priorities and interests may be quite different. Plus there's no such thing as a perfect telescope. Consider all options, read the product reviews, and find out what other people think of their own telescopes. Best of all, star parties give you a chance to look through different scopes and even get the feel for what it takes to handle one.

Remember that with a larger scope comes more grunt effort. Indeed, on any given night, a modest scope under the stars beats a big scope in the closet! To quote Yoda, the Jedi Master of Star Wars, "Size matters not".

Aperture lust does have one big benefit - it's great for other amateur astronomers who then have a source for good used telescopes at more affordable prices.

Finally, Internet telescope guru Ed Ting offers this oftrepeated advice: "Avoid 'paralysis-by-analysis'. If you spend more than an hour a day reading telescope catalogs, you are probably in this category. Just get something; you'll feel a lot better."