Saturday, November 22, 2003

The Joys of a Good Refractor

I was just outside looking at Saturn with my Televue Ranger. It's in the low 20s, crystal clear, and not very turbulent. I hauled out the Ranger because Saturn is still too low in the east for me to get with my 8" reflector--the disadvantages of living in suburbia. This was also a chance to try out the 4mm University Optics orthoscopic eyepiece I just received in the mail. (I have been doing business with University Optics since 1971--I have nothing but nice things to say about them.)

I should explain. About ten years ago, I received a no-name 4mm orthoscopic eyepiece as a gift for helping a friend find a buyer for his Coulter 13.1" reflector. The no-name was a little dirty, and you could see the dirt when you looked at bright objects. I decided to take it apart, and clean it.

It turns out that there are many ways to reassemble an eyepiece. An orthoscopic, at least a true Abbe design orthoscopic eyepiece, consists of two chunks of glass: an eye lens, and a triplet field lens. Neither of these are symmetrical, so there are four possible ways to put the eyepiece back together.

When I was done, the lens wasn't really any cleaner--and it was no longer a 4mm focal length eyepiece--more like a 5.5mm. I bought a 4mm orthoscopic that someone had just bought--and discovered had too little eye relief for them to use while wearing glasses, so I was able to buy it for $10 off the new price.

I was about ready to sell the dirty no-name orthoscopic cheap to anyone with the patience to clean and reassemble it, when someone gave me directions on how to reassemble it correctly. I took the no-name apart, cleaned it, and reassembled it. Voila! It is not perfectly clean, but there's only one obvious dirt spot now, and it is again a 4mm orthoscopic. (I'll be quite happy to take $25 for it, shipped anywhere in the U.S. or Canada.)

Anyway, back to the story of chattering teeth and my dog whining about the cold in the backyard. As Saturn rose, and less and less atmosphere was in the way, more and more detail became apparent. The joy of a well-made refractor is that it gives such an astonishing image, even at relatively low magnification.

The 4mm orthoscopic (120x in the Ranger) was just beginning to give hints of the Cassini Division at the ansae when it became too cold to stay outside--and I could see differing cloud bands in the atmosphere of Saturn. This is a moderately demanding task in many reflectors of 6" aperture--and in a refractor of 2.7" aperture, all the more impressive.

Using a 9mm orthoscopic and a 3x Barlow took me up to 160x. The image was beginning to lose sharpness at this point, but not enough to make me give up on it. The contrast drops as you increase magnification, and so the Cassini Division was a little less obvious. The cloud bands in the atmosphere were a bit less crisp as well, but still noticeable.

The Ranger is a semi-apochromat--not completely color-free, but much better than a typical achromatic refractor, though a bit inferior to a true apochromatic (color-free) refractor. I am attempting to purchase a Vixen 102S from someone in Spokane at the moment--this should provide a dramatic leap up in resolving power and magnification. (Then I have to find a buyer for the Ranger.)

If you are at interested in refractors, you may find this review I wrote several years ago of the Televue Ranger of interest. Like nearly everything I write, I was unable to get it published anywhere.

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