Revised 11-02-2004

I hope the following history of the apochromatic lens designs made by Roland Christen of Astro-Physics is of some interest to the readers. I do not claim complete accuracy.

The first ad that I am aware of was in Sky and Telescope magazine, December 1981. Two lenses were offered: A 6" f/11 magnesium fluoride coated oil triplet for $1800, and an 8" f/11 for $3600, both in cell. These lenses proceeded Roland's article in Sky and Telescope, October 1981, page 376, "An Apochromatic Triplet Objective." This was a groundbreaking article, and was the beginning of the new age of Apochromatic refractors. The prototype was a 5" f/12, and was shown at the Riverside Telescope Making Conference. The images of Jupiter impressed the attendees beyond any telescope on the field, and won the prize for the most innovative optical design.

Roland was very fortunate to find a large supply of an abnormal dispersion flint, similar to Schott KzFS-1, but even better in its color correcting properties. In fact, it was ordered by NASA, but was never used. When Roland found that the supply was available for sale, he gladly bought it up. By-the-way, this "NASA" flint glass was the ultimate in short KZ flint glass. No manufacture supplies a flint glass that can match its abnormal dispersion properties today. The next ad was for two new apochromatic scopes. A 5" f/6 for $950, and 5" f/12 Super Planetary for $975 (what a deal, ask yourself what a 5" apo costs today!). These were complete scopes. They used a design of BK-7/KzFS-1(NASA)/BaF-10 or BaK-1/KzFS-1/BaFN-10 glass.

Then came the infamous 6-inch f/9 NASA triplet, which only (it is said) ~24 were made. The scope was advertised in the July 1984 issue of Sky and Telescope, and priced at a slightly rich $1695, for that time. For another $1300, you could have a complete mount and custom tripod. Astro-Physics then expanded their line to a 4"f/6 ($795) and 5" f/6 ($995). This 5" model had the highest aberration residuals of any Astro-Physics refractor ever produced, but made a fine low to medium power refractor. If this lens was stopped down to 4", it gave good high power views too. It was simply too large and fast before the advent of ED glasses. The last model in the line was a replacement for 6-inch f/9 NASA triplet, the 6" f/8 ($1295), which used KzFSN-4 as the abnormal dispersion flint element. The color and spherochromatism of this model was slightly less well corrected than the older 6-inch f/9, but was $400 cheaper. Interesting that the stated quality was 1/56 wave RMS, virtually the same as today.

At this point, Roland's success made for a big life decision. Quit a safe, well paying job, or go full time into telescope making. The choice was made, and with the help of his wife Marj, and Fred Mrozek (of APOMAX fame – in which Fred made a limited run of superb 5.2" and 8" apochromats), and Fred's father Chester Mrozek (who supplied tooling, a grinding/polishing machine and other important ideas), Roland went into the full time telescope making business.