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by Jay Reynolds Freeman
On Wednesday, 12 May 1999, I took my 70 mm f/8 Vixen fluorite to the TAC [The Astronomy Connection] close-in site at Montebello Open Space Area, in the hills above Palo Alto, California, for some Messier hunting. Many people had planned to go, but few went -- high winds and fog skimming the ridge line in the afternoon had proved scary. But the wind died, and though fog threatened, our parking-lot setup area stayed free of it. I had about two hours of good observing, terminated simultaneously by the onset of dew and cirrus, and by my need to go home and sleep.
I have been doing this Messier survey -- the one with the 70 mm is my twenty-third -- mostly using a Vixen 8-24 mm zoom eyepiece, and have acquired enough confidence in that unit that it was the only eyepiece I brought with me on the 12th. The images are decent at f/8. The range of focal lengths spans 23 x to 70x for the little Vixen, which is a good portion of the useful range of magnifications for deep-sky work with a 70 instrument. Furthermore, the eyepiece's apparent field of view does not contract enormously as its focal length is set to longer and longer values: Some older zoom eyepieces show you the same piece of sky at all magnifications, so that the view at low magnification is disturbingly narrow. Thus the 8-24 mm zoom is useful at its lowest magnifications for finding things -- the apparent field of view is about 45 degrees at 24 mm, so that the actual field of view, at 23x, is roughly two degrees.
Casual use of the finder easily got me to within a degree of all the Messier objects on my list, and once I had them visible in the main telescope, I could adjust the magnification for the best view. The range of magnification that gave the best view was often surprisingly narrow -- changes of ten percent were enough to make noticeable differences. Thus an 8-24 mm zoom substitutes for half a dozen or more conventional eyepieces, instead of the two or three that I had supposed when I bought it, making it rather a bargain. I looked at the focal length setting that worked best occasionally, after I had set it, and most often found it near 12 mm.
The evening's targets included nearly all of the Messier galaxies in Virgo, Coma Berenices, Canes Venatici, and Ursa Major, plus a few globulars. They were all easy to see in 70 mm. A few galaxies showed hints of structure -- elongation or bright nucleii. I could see the companion to M51, but not the "black eye" in M64. I spotted NGC 4387 and 4388 near M84 and M86, M3 and M5 showed hints of granularity at 70x, but M53 did not. M4 probably would have, but it was way down in the murk to the southeast, as was M80. I logged 25 Messier objects for the night, and have three to go to complete the 70 mm survey.
I helped another observer with a C8 to identify some NGC galaxies, and we both showed things to an out-of-town guest who was traveling to the area and had heard about our star party on the Internet.