The July report can be brief so far as photons go: none, zero, nada. Not only was New Mexico slammed with relentless cloudy skies, but much of the nation was (as noted on various Cloudy Nights threads). However, my old photon collecting pal Eric Jacob did well this month. You can see his work on his CheapSkate Astrophotography webpage.
My report consists primarily of an equipment update. The main events (skipping over ancillary purchases) are:
(1) the CG5 has found a welcome home in Eric’s hands. He’s running up to two minute unguided exposures with about a 50 percent usable rate.
(2) I replaced the CG5 with a second CGE (used). That’s a long story that I won’t go into.
And (3) I purchased a new Takahashi astrograph. That’s a long story that I will go into.
Making the transition from visual astronomy to astroimaging means – at least for me – a continual shaking out and revaluation of the equipment. Astroimaging equipment reminds me of the time when I first became passionate about fire arms, particularly shotguns and center-fire rifles. I must have owned and sold at least twenty different guns before I finally wound up with the keepers.
I started the month with a long standing order for a TMB 130SS APO f/7 at about 900mm focal length. No doubt this is a fine telescope. It’s received nothing but rave reviews. But after repeated queries to the vendor yielded nothing more than "we’re trying to fill orders as fast as possible," I began to rethink the entire issue. "Why duplicate the SV115APO?" became the question of the month. "After all, Max, you’d only gain about a half inch of aperture. Why not try something else?" The something else, as it turns out, is a Takahashi Epsilon 180ED – 500mm focal length at f/2.8. More on that instrument below.
Dean Rowe, a fine and very experienced astrophotographer, and owner of a Tak 180, helped me think the decision through. His advice was reassuring. One of the great things about the astroimaging community is the willingness of almost all its members to share their insights generously. Thanks to Dean. You can view his outstanding work on his website.
The Tak weighs in at 22 pounds, just about the same as the TMB130 would have. The Takahashi Company has a fine reputation, and from what I can see without actually using the new instrument, it’s well deserved. "Built like a Mercedes" is the phrase that comes to mind. Flawless paint and fit everywhere. Five year guarantee. And state of the art technology. Or so this old man is led to believe.
So what are the innovations? To simplify, Tak took the basic premise behind a Schmidt Camera – combining a convex mirror with a concave surface yields a flat field – and improved upon the design. According to Wikipedia, "The Schmidt camera was invented by Bernhard Schmidt in 1930. Its optical components are an easy to make spherical primary mirror, and an aspherical correcting lens, known as a corrector plate, located at the center of curvature of the primary mirror. The film or other detector is placed inside the camera, at the prime focus. The design is noted for allowing very fast focal ratios, while controlling coma and astigmatism." (Source)
Takahashi designers, aided by computers and contemporary glass, created a hyperbolic ED (extra-low dispersion) glass corrector (the concave surface) combined with a precisely ground mirror (the convex surface) to yield a 44mm image circle. The user’s manual notes: "Since the stars in the field of the E-180ED are only 10 microns [in diameter], very precise focus is needed to keep the stars pinpoint on the image." Yah, I bet so. The manual notes that the instrument was specifically designed for the new generation of large frame CCD cameras. Gee whiz, I might just have to get one.
Max
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