Advice and Consentby Dale IbisLike most amateur astronomers, when I started out, I read everything I could lay my hands on about telescopes and binoculars and how to go about becoming an amateur astronomer. I must say that there was a bewildering array of material on the subject, most of it filled with a variety of absolutes such as: 
Let’s start with aperture.Yes, aperture is important. No, aperture is not everything. Simple geometry tells one that the bulk and weight of a telescope increase as the cube of the aperture. So, if one doubles aperture, all other things equal, bulk and size increase by eight times. Most of us live in urban areas and wish to transport our telescopes to remote locations. Smaller is definitely better here. If you don’t use your telescope, it doesn’t matter how large it is.
Refractors.The best telescope I ever owned, and the one that showed me the most, was an inexpensive 3-inch f/15 refractor. It showed me so much because it was light (about 20 pounds complete), showed the planets and the moon better than reflectors of 6- and 8-inch apertures, and never required adjustment. I also own a 4-inch refractor, and while it definitely shows more than the 3-inch did, it also weighs much more, and is therefore used less in my backyard.Refractors can be extremely good amateur instruments, highly portable and easy to care for. Most important, while affordable refractors have little aperture, they usually have excellent optics, far better than commercial reflectors or catadioptrics. Refractors should not be written off by amateurs, especially beginners. Try one – you might like it. "Magnification is bad – low power, wide views are more desirable."Not necessarily. Experienced astronomers know that increasing the power on deep-sky objects increases the contrast, sometimes dramatically. And, of course, on the planets, you want to use the highest power possible consistent with seeing. Kick up the power if you feel like it and your mount can handle it. This is a hobby! If it feels good, go with it!"The eyepiece is half the telescope."Nonsense! This is a myth that results from large aperture telescopes with short focal ratios. Short focal ratios produce steep light cones. Steep light cones require complex eyepiece designs to avoid severe edge of field aberrations, especially with fields over 45 degrees wide. The center of the field is still good. After a great deal of testing of eyepieces, I believe the best, sharpest images are to be had from quality Orthoscopic eyepieces. The only loss with these is that their fields are 45 degrees or so. However, they are half or less the price of other more complex designs, and work very well down to f-ratios of 4 or 5."Serious astronomy requires at least 6 inches of aperture."More nonsense. How many of us are writing research papers or submitting observations to professional bodies? Forget it! Anything from 2 inches up is enough to have fun."The moon is an amateur’s enemy and the planets require professional level optics."Wrong! The moon offers tremendous variety with different views every night. I have never looked at the moon and seen exactly the same thing twice. Moreover, it is accessible to urban and rural dwellers alike and is completely immune to light pollution. The moon is an amateur astronomer’s friend.The planets have something to show everyone, even binocular observers. The moons of Jupiter, rings of Saturn, and phases of Venus are available to virtually any telescope and most binoculars. Again, we are not all trying to do "serious" astronomy, we’re trying to have fun. So have it! "Binoculars for astronomy should have a 7mm exit pupil."This bit of advice is difficult to understand. Binoculars are small telescopes. We never see telescope sages advising that we should always view through telescopes with a 7mm exit pupil! The best binocular views I have ever had were through 20x60 binoculars with a 3mm exit pupil. If the view is good, use it. Forget the exit pupil business! And binoculars are not only good for beginners, but experienced amateurs will find a new interest in the night sky using binoculars. Their ease of use and ready portability are an unbeatable combination for anyone.Central obstructions definitely deteriorate telescopic performance.A 33% (by diameter) obstruction is as destructive as a 1/4-wave error. If your optics already have a 1/4-wave error, and most commercial reflectors do, then your total error with a 33% central obstruction is 1/2-wave. Most of us can definitely tell a 1/2-wave error. Obstructed telescopes require top-notch figures on the mirrors to achieve 1/4-wave performance.However, that doesn’t mean that obstructed telescopes are never good. Again, reflectors can be made large in aperture less expensively than refractors. A lot of sins can be covered with a large aperture, so if the view is satisfactory, go with it. "Equatorial mounts are a virtual necessity."Quite the contrary, equatorial mounts are a necessity only if you are doing long exposure astrophotography. For virtually every other use, an altitude-azimuth mount will work just fine and weighs 50 to 70% less that an equatorial. Witness the explosion of Dobsonian mounted scopes. Amateurs have discovered the virtues of alt-az mounts, even if some of the gurus of our hobby haven’t.My personal way to bypass the big ten absolutes has been to "go small." After 15 years in the hobby observing with everything from 60mm refractors to 12-inch Newtonians, I’ve decided that a 3-inch APO refractor on an 
alt-az mount weighing 16 pounds and 20x60 binoculars weighing 3 pounds will be
the mainstay of my hobby. Already, I’m finding myself observing more. Virtually
every clear night I find myself in the yard viewing the moon, a planet, double
stars, and large, bright clusters and nebulae. Gone is the requirement of
willingness to lug 60 pounds of equipment back and forth to the garage or shed.
A clear night and two minutes is all it takes now. Further, the refractor is f/8, so
Orthoscopic and Plössl eyepieces are more than adequate to give me great views.
I have gone for high-quality, unobstructed optics and have learned to relish pinpoint
stars and clear, sharp views of planets and the moon. I also have a pair of 7x50 binoculars
for real quickie views and for travel. I have had views of deep-sky objects with binoculars
in the mountains that would rival a 12-inch Dob in suburbia.Over the years I have learned to ignore the absolutes and go with what works for me. Whether you are a beginner or an old hand, I would advise you to ignore the absolutes and find your own personal path. You’ll never be sorry! Clear Skies! Copyright ©1998 Calumet Astronomical Society. |
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