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Eyepieces

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Posted by Daniel Johnson on October 31, 2002 07:13:35 UTC

Plossls are a cost-effective improvement over the SMA design.
I'm assuming the Celestar has the same standard Schmidt-Cassegrain threads on the back as any other Celestron or Meade SCT. If so, a good way to get broad-field views is to buy the f/6.3 focal reducer that Celestron and Meade sell. For eyepieces, it works like a Barlow in reverse, allowing lower power for your scope. With it, an eyepiece of 25-to-32mm range will give a good broad-field view. That same eyepiece can also give a medium power without the focal reducer, of course. It's nowhere near as convenient to put on and remove as a Barlow, so putting the focal reducer on and off many times per night is not practical. Still, it costs less and has more uses than 2-inch eyepieces, which you would otherwise have to use to get the lowest useful powers available for Messier objects. At f/6.3, the difference in quality between Plossls and SMAs is more evident; the Modified Achromat (Kellner) eyepieces don't handle short focal ratios well.
For high powers on an AVERAGE night, about 30x per inch of aperture is decent. At times you can reach 50x, but it takes a steadier-than-average night. I spend most of my planetary viewing time at 25 to 30x per inch, though I live for those nights when I can use 40 or 50x per inch of aperture. You'll get more use out of a 9 or 10mm eyepiece than a 6mm or 4mm, so get a 9 or 10mm first. Later, for those rare nights, get the really high power stuff.
If you want a really fine eyepiece, you can't go wrong with anything Televue makes. I own a couple thousand dollars' worth of their eyepieces. But for the cost of one Televue Radian or Nagler, you can get the focal reducer and two decent Plossls from other manufacturers--more bang for the buck. (But holy Toledo, I love my 10 mm Televue Radian.)

--Dan Johnson

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