Star Points for November 2010 by Curtis Roelle Advice for Telescope Shoppers Coming If you're looking for a telescope and a place to turn to for advice, the Westminster Astronomical Society can help. The club will hold its annual Telescope Buyers Workshop (TBW) on Wednesday, November 10, at the Bear Branch Nature Center (BBNC), starting at 7:30 p.m. The event is free and open to the public. Adjusted for inflation, telescopes are cheaper than ever and a buyer's dollar goes very far. Also, telescope consumers have a greater selection of products than at any time before, and quality continues to improve. In spite of all the choices on the market, there are two basic kinds of telescopes – the refractor and reflector. The refractor uses a lens and the reflector uses a mirror to gather light and funnel it into the eye. One thing both types have in common is their "aperture" or the diameter of the lens or mirror. This is probably the single most significant factor when selecting a telescope. In general, larger the aperture, the fainter the objects the telescope can reveal. Price also increases with aperture, however, and so does telescope weight. These are only a few of other important factors. A refractor is more expensive than a reflector of similar aperture. This is because a refractor's glass must be clear and finished on both sides. A reflector's mirror is only finished on one side, so the glass can have defects, such as bubbles, without affecting its performance. Refractors and reflectors each have a variety of subtypes, based on optical design and materials used. They can't all be described in this column, so I'll just mention a couple types of each. Refracting telescopes have a clear lens at the front and an eyepiece at the rear. The lens typically consists of two (doublet) or three (triplet) different kinds of glass. The objective is to bring the different colors of light to a common focus, reducing color dispersion, or that unnatural "rainbow" around bright objects. In general, doublets are called achromats and triplets are called apochromats. An achromatic lens focuses colored light better than a single lens, and an apochromatic lens does an even better job, but at greater cost. Looking at telescopes in today's market, I see apochromatic triplet telescopes with a 3-inch aperture going between $700 and $1200. And that doesn't include a mount to hold it. A larger 5-inch telescope with achromatic doublet goes for around $400, without a mount. A 6-inch achromatic with a mount can be found for $1100. Twenty years ago a telescope with a small 3-inch achromatic doublet sold for $450-$500. Today, that smaller telescope would cost $752-$836 in 2010 dollars. Reflectors hold a mirror in the bottom of their tube. A Newtonian reflector telescope has an eyepiece sticking out the side of the tube. A Schmidt-Cassegrain (SCT) telescope has an eyepiece in the back, like a refractor. An SCT is more compact and expensive than a Newtonian with the same aperture. An inexpensive 6-inch Newtonian, with a mounting and motor drive can be purchased as low as $420. Twenty years ago they sold from $600 and $800, or $1000 to $1400 in 2010 dollars. An 8-inch SCT, with mounting and motor drive, sells for about $2600. In 1990 one might cost $1900, or $3175 in 2010 dollars. Much of a telescope's cost can be in the mounting. One alternative is the Dobsonian, which is a Newtonian in a simple inexpensive, but steady, mounting. An 8" Dobsonian costs around $330. In 1990 they cost $275, or $460 in 2010 dollars. These prices are representative only. They are based on advertisements I've recently seen, and others from back issues of magazines. The telescopes and apertures discussed above are ones that I think a buyer would be satisfied in owning. They will give an observer years of satisfaction and good service. However, in this short column I haven't even touched on the many advantages offered by each type. That is what the TBW is for. Gary Hand, owner of Hands-On Optics in Damascus, will be present in order to answer questions from telescope shoppers, be they first time buyers or looking to move up. If you have a telescope on your holiday shopping list, for you or someone else, you need to attend the TBW at BBNC. With the current installment, this column marks the start of its 15th year. I want to thank you, the readers, for being such a fine audience.