Modern Tests Of Historic Refractors

[herbhighstone]

Hello to all the folks --

In the past, opticians were quite secretive about their fabrication and testing methods for refractor objectives. Thus the historic information about lens testing is somewhat scanty. For an interesting review of historic test methods, you should Google "Testing of Telescope Objectives In Historic Times." Some of the information quoted in this site is quite rare. I'd certainly be interested, for example, in obtaining Brashear's optical testing articles that were published circa 1900. I've never seen these articles, nor for that matter any other reference to them.

It would be fascinating to compare Brashear's methods to Hasting's refractor telescope work. Hastings had his optical design system so fully perfected that the opticians could complete one of his lenses from spherical surfaces with only 10 minutes of touch-up figuring. To Hastings, aspheric figuring was a needless bother that he preferred to avoid by his celebrated design tricks. Very nice!

If you Google "Our Brashear Objective Lens" you'll find some nice interferometric images of the performance of a century-old refractor objective. There are also some highly detailed photos showing how an expert technician disassembled this antique lens for cleaning and restoration. Modern tests show that Brashear did some very fine optical work, especially considering that he worked a century ago.

Naturally I'm also reminded of the classic and now famous 13 inch refractor by Henry Fitz, who preceded Alvan Clark in the refractor world. This amazing refractor was very successfully demonstrated at the 1996 Stellafane Conference, to which it was driven in a U-Haul truck, complete with its new plywood portable mount. And it worked just great! I wonder if I could make such a thing? Or even carry it across the parking lot? No, and no!

Fitz used extremely thin lens elements to "grind away" glass homogeneity problems. Naturally, the thinner your lens, the fewer glass problems will remain in the field of view. I wonder if any forum member with Oslo or something similar has ever analyzed the design of this 13 inch Fitz lens? Its fine performance astonished expert observers at Stellafane.

Has anyone reading this message ever restored an antique refractor lens? And if so, where could we see some photos of the work?

Best wishes from Herbert Highstone, JUNIOR Member (I'm so thankful, at the age of 65 years, to be JUNIOR in any organization whatsoever. It almost makes me feel like I'm 50 once again. Talk about the fountain of youth! )

[Rick Keppler]

Hi Herbert,

You raise some interesting questions. I hope someone can shed some more light on this ok, ok, I know, bad pun. While I'm not so interested in the techniques they used, I am interested in the results they got. More (as in more of them) modern interferometric tests of older glass would be interesting to see and discuss.

[Tailwag]

Hi, can you tell me if you came across any John Browning or George Henry With links of interest in your search for test results?