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Observing hidden treasures.........
Last night it was clear between 11 and 1 o clock (local time) and I had a quick look at some deep-sky objects with just to test my new eyepiece, the 21mm Denkmeier. In my dob, the 65-degree eyepiece gives a magnification of 76x and a true field of view of 51'. I pointed the eyepiece at M 27 and although it wasn't really dark (grey nights during the May-July period), it was quite an impressive sight. M 27 is really big, even at low powers, and with the UHC filter the Dumbbell shape is very obvious at first sight. The 21mm Denkmeier seems to be very "transparent", letting through much more light than the 20mm and/or 25mm Vixen Lanthanum. The stars where sharp right to the edges although I think that there is a little pincushion distortion along the edges. What I really love about this eyepiece is the generous 20mm eye-relief. Even with my glasses on, I can take in the whole field of view at once.

The second object for the night was M 13, the big globular cluster in Hercules. The 21mm showed too much of the grayish sky, but M 13 was already resolved very well. The best view I got with the 7mm Pentax XW (230x). The cluster was completely resolved, even under these mediocre conditions. There were a lot of long streams of stars extending from the bright core. It looked more or less like a big spider. The three dark diverging lanes, which should look like a propeller, stayed invisible again. Probably I need a better seeing and a darker sky for this.

After M 13 I turned the dob toward NGC 6210 (Hidden Treasure 78 from Stephen J. O'Meara's book, Hidden Treasures). Already at the lowest magnification (76x) with the 21mm Denkmeier, this planetary Nebula looks like a deep-blue little disk. Using higher magnifications up to 230x made it look a lot bigger, still blue, but not so blue as with the lowest power. The seeing didn't allow higher magnification, so I could not go for the real details. According to Phil Harrington (The Deep Sky: An Introduction) this planetary takes high magnifications well, and is at its best 150x or more.

I ended my little tour with two objects I had never observed before, Hidden Treasure 94 (The Flying Unicorn Cluster) and Hidden Treasure 18 (The Ghost of the Moon) from the Additional list from O'Meara's latest Deep-Sky Companion. HT94 (NGC6709, Collinder 392), the Flying Unicorn Cluster, is a wonderful open cluster in Aquila. At low powers (78x) the triangular shaped cluster is very obvious, with some very nice groupings of (colored) stars. Although high magnification (230x) revealed more stars, I liked it most in the 12mm Nagler with a magnification of 133x. The cluster was nicely framed, some 40 to 60 stars with some "space" left around it. The colors came out even better than with the low power view, and I could detect quit a few "double-stars" or groupings of several stars; a very nice object, which I will definitely visit again under better conditions.

HT 18 (NGC 6781) from Appendix C (Twenty additional hidden treasures is) is a magnitude 11 planetary, about 2' in diameter. Without filters this big planetary is not so easy to see, but with the UHC filter in place it is a perfectly round, very bright and easy object. There should be some details visible at higher magnification, but because of the bad viewing conditions I did not try this last night, but again a very interesting object, which was completely unknown to me. At the moment this hidden treasure list is my favorite a perfect alternative for those who have done the Messier and Caldwell catalog. I will be back with more observing details on these interesting deep-sky objects, but I will need a darker and more stable sky. Until then, Clear Skies to all of you!

Oh, and the Denkmeier eyepiece is a perfect match for my 300mm f 5.3 dob. If you wear glasses or want a good eye-relief for any other reason, I can highly recommend this relatively small and compact eyepiece.

image
The Denkmeier 21mm eyepiece compared to the T4 12mm Nagler


Posted by Math on 07/14 at 10:54 AM
Deepsky observing • (0) CommentsPermalink

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