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Don Pensack

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Everything posted by Don Pensack

  1. I find the TeleVue Bandmate II O-III (2018+), the Astronomik O-III Visual (2018+), and the Lumicon Gen.3 O-III all equal in the field. You can't lose with any of them. My own personal filters were lab-tested and here are the results: Filter bandwidth FWHM H-B line O-III (1) O-III (2) H-a low wavelength High wavelength Astronomik O-III 2017 12 N/A 92.9 93.9 N/A 493 505 TeleVue O-III 2018 12 1.6 99.2 98.4 N/A 492 504 New LumiconO-III 2018 11 3.5 95.1 94.7 N/A 494 505
  2. Many years ago, my friends and I compared the XL Zoom in a Pentax 80mm ED spotting scope with 3 focal lengths of Pentax XW eyepieces in the same scope. We discovered: --the images were a LOT brighter in the separate eyepieces, even matching focal lengths --the images were a lot sharper in the separate eyepieces --the field curvature of the zoom was more than the separate eyepieces --the sharpness of the separate eyepieces was superior to the zoom. With the zoom, the spotting scope was just average. With the separate eyepieces, it was up there with Leica, Swarovski, and Zeiss in terms of performance. After what we saw, I can no longer recommend the XL (SMC) Zoom. Certainly it is a lot less expensive than a Leica, but it is more than the Baader, which I rate to be a better zoom.
  3. Yes, the interaction of a barlow with the curved field of a refractor would be different than the interaction of the same barlow and a flatter field reflector or perhaps a refractor with a field flattener. Likewise, the spherical or chromatic aberration of the telescope objective would play differently after passage through the lens. Then, the position of the focal plane in the eyepiece barrel will determine the exact amplification power of the Barlow, so it might vary from eyepiece to eyepiece. I owned one of these 3 element short Japanese Barlows in the '90s, and they were quite good (sold as Parks Gold Series, Celestron Ultima, Orion Shorty Plus, etc.). But they weren't quite the equal of a few of today's top Barlows (e.g. Baader VIP, TeleVue PowerMate) when it came to being essentially the same, optically, as a short focal length eyepiece without a Barlow. Still, a very good Barlow and it sounds like a good "find".
  4. Since the Ethos comes in 21mm, 17mm, 13mm, 10mm, 8mm, 6mm, 4.7mm, and 3.7mm while the APM/Lunt HDC XWAs come in 20mm, 13mm, 9mm, 5mm, and 3.5mm. it would appear there is only one focal length in common. Some enterprising soul needs to acquire a complete set of each and do in-depth comparisons for us all (and don't suggest I do it--I don't get enough observing time in as it is!).
  5. You must have a long focal length scope. I typically use a 13mm or 10mm eyepiece on that group (my scope has an 1825mm focal length). 20-21mm would seem to be a bit low in power.
  6. The same eyepiece is also sold under the Astromania, Knight Owl, Olivon, Omegon, and TMB labels as well as BST and Sky Watcher. They are quite competent eyepieces and work well in scopes of f/6+ (shorter focal ratios will induce some edge of field astigmatism) Among the various brands, they are available in 2.5mm, 3.2mm, 4mm, 4.5mm, 5mm, 6mm, 7mm, 8mm, 9mm, 15mm, 20mm, and 25mm If I were starting out again, instead of the junk I used then, these would be on my radar screen as a "best buy" eyepiece, along with the Celestron X-Cel LX, Meade HD60, and the various brands of BST eyepiece sold as Astrotech Paradigms, BST Starguide, etc. (about 6 different labels for that one). This inexpensive 58-60° type of eyepiece is more comfortable to use, has a wider field, and general better mechanical structures than the ubiquitous inexpensive Plossls sold under 50 brand names. I like the eyecups on these (once the oil underneath is wiped off).
  7. The MWA and XWA are from two different manufacturers. It will be interesting to see if the reviews of the MWAs are favorable, since they are, at the moment at least, a little less expensive than the XWAs were. 100 degree eyepieces are getting popular. It seems a new one springs up every month, though, to be fair, many are the same eyepieces with different private labels on the outside. Every now and then, someone makes a design change that favors use (example: the new Lunt 100/110 degree eyepieces). I'm glad to see the expansion of interest: Agena, Explore Scientific, Lunt, Magellan (KK), Meade, Omegon, SkyWatcher, Telescope Service, TeleVue, William Optics, Nikon. Now, if only someone other than Explore Scientific became interested in 120 degree eyepieces.
  8. Just a note: In the pressure chambers where the eyepieces are assembled, it doesn't matter what gas is used. However, under nitrogen the seals in the machine fail more often when nitrogen is used than when argon is used. Since refitting the machine with new seals means down-time and lost production, argon, though more expensive than nitrogen, results in increased production and lower per-unit cost than using the less expensive nitrogen. Any claim this makes any difference to the end user is advertising hype. ES has entirely changed over to Argon, though they still have stock of 20x100 in N2 version. From the standpoint of amateur astronomers, it makes no difference which gas is used. My own eyepieces are pressurized with a nitrogen-oxygen-argon mix to 14.7psi. Always have been.
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