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Don Pensack

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About Don Pensack

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    Star Forming

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    Audio, films, traveling, and astronomy of course.
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    Los Angeles
  1. Mark, These eyepieces, made by KUO in China, are available under several different labels. You should pick this up to see all the 100-120° eyepieces currently available: https://www.cloudynights.com/topic/657524-2019-eyepiece-buyers-guide/
  2. I commented on how to find the ideal setting for an eyepiece in my late post in this thread: Look at the post just before his. Your "zero" setting is setting 3, the middle position, if using the tape technique.
  3. It was the pre-production prototype brought to the star party by Al Nagler himself.
  4. As of September 12, they are in production and the initial run of ~30opcs will be delivered to TeleVue some time in the Fall. Alas, at this writing, we still have not retail price.
  5. They are a modern updated equivalent of an Abbe orthoscopic, that is they are a narrow field (42°) with high resolution, intended for high power views of planets, moon, double stars. There was a brief production quality-control problem with the 3.4mm, though that is now fixed. The shorter focal lengths did not experience that. They are good alternatives to using other eyepieces with, say, a Barlow lens, to achieve ultra high powers in small scopes of short focal length.
  6. There is an empirical way to find the right setting for an eyepiece. You only need to do this for 1 eyepiece. For every other eyepiece you own or will own, you simply insert the other eyepiece and focus using the Tunable Top. Whatever setting results is the correct setting for that eyepiece and you can pre-dial it before you put the eyepiece in in the future. So, Insert the eyepiece with the tunable top set to its maximum out setting (H). Focus the scope and look at stars at the edge of the field (or move a moderately bright star to the edge of the field). Still see coma in the star image? Then dial the top in one setting to G , focus the scope and repeat your evaluation of a star at the edge (it's easier to see coma on a brighter star, like Polaris, than a dimmer star). Still see coma? Keep moving in one setting until, when you focus, the star at the edge of the field displays no coma. That is the setting you'll use for that eyepiece in the future. For every other eyepiece, leave the focuser where it is and focus using the tunable top. Write down the settings so you know what they are. You can do this with any eyepiece from any company. If the eyepiece needs more outward movement of the tunable top, you can add a parfocalizing ring to the eyepiece to raise it a bit. If the eyepiece needs more inward travel of the focuser, you will have to settle for the inward most setting (A): example Nikon HW 17mm. What you do by doing this is to set the Paracorr in the light cone from the primary. There is one more way to do this: insert the Paracorr in the focuser in setting E. Place translucent scotch tape across the opening of the Paracorr in an X shape where the eyepiece would normally go. Point the scope at the moon and focus the telescope with the moon's image on the translucent tape. When the Moon is in focus, you have found the perfect setting of the Paracorr in the light cone from the primary mirror. Lock the focuser in this position, and insert each one of your eyepieces in sequence, focusing on the Moon with the tunable top. The settings each eyepiece uses is the correct setting for that eyepiece. I have done both and am happy to report that, at most, I was about a half setting off on an eyepiece or two that way, and a half setting is a very small error (about a mm). The problem with both methods is if the observer is nearsighted. In that case, perform the test(s) with glasses on that correct your vision. Otherwise the settings for each eyepiece will be off. Later, when you view without glasses, the distance between the eyepiece and Paracorr will have already been accurately determined and even if you have to move the focuser in to focus, the correction will be approximately correct.
  7. Bear in mind these are the same as the Meades, and lab tests show they are not really 100° fields, more like 88-90° Look for test reports on the Meades to find reviews. There are other 100-110° eyepieces marketed by many companies (APM, Lunt, TS, StellarVue, William Optics, SkyWatcher, et.al.) that are made by KUO and are legitimately 100-110°.
  8. KunMing United Optical (KUO) is the manufacturer of the 100/110°: Lunt APM StellarVue SkyWatcher Telescope Service William Optics It's unrealistic to think that the coatings are different in any of them--the manufacturer couldn't make any money doing that. As to who makes the 100° eyepieces that are really closer to 90° (like the Meade), I don't know.
  9. It's my favorite TeleVue Plössl. It's 49.5°, and the edge illumination is a tad vignetted, but that doesn't matter when you look through it. You may acquire a lot more eyepieces in upcoming years, but this one should stay with you. There aren't many eyepieces like this one I regret selling, but this is one of them. Of course, I can always get another, LOL.
  10. If you have one labeled 72°, it's a "collector's item". It's like the 2" Olivon 70° eyepieces with 1.25" on the barrels. Oops. Like a double-stamped coin, or some cars a few years ago recalled because they had a different name badge on the rear from the model they were.
  11. I kind of look at the TV filters as special versions of the Astronomiks (Astronomik makes them for TeleVue). I've seen some recent Astronomiks edging up on 98% transmission, too. In the field, though, I've been unable to see a brightness difference among the 3. Remember, a 10% difference is only 0.1 magnitude, which is much less than the hour-to-hour sky variation at most sites.
  12. They have more elements than Plössls and are larger and heavier. As a result, eye reliefs are longer than Plössls and so they are usable down to 3mm focal lengths. But, like many ES eyepieces, control of astigmatism at the edges in fast focal ratios, or control of internal light scatter, are the two places where they don't measure up to the high end eyepieces. Bear in mind, these are very inexpensive eyepieces, so match your expectations to the price. If you look at it that way, they are good eyepieces.
  13. Many of these eyepieces are from the Chinese firm of United Optics in KunMing (KUO), They are sold under Telescope Service, William Optics, SkyWatcher, StellarVue, and Lunt/APM labels. There are slight differences in the barrels.
  14. Since the light rays after the Powermate are parallel, it should probably go first since getting the eyepiece correctly placed relative to the Paracorr lens is critical for best coma correction. FWIW, my best lifetime view of Jupiter was with PowerMate + Paracorr + 8mm Ethos, at 456x, in literally perfect seeing (Pickering 10).
  15. In essence: the Paracorr 1 corrects a 40mm field width down to f/5 and is close to that at f/4.8. The Paracorr 2 was developed for faster scopes and corrects a 40mm field completely down to f/3.5. The Paracorr 1 had a range of 12.7mm, and some of today's eyepieces were outside the range of travel (notably 31mm Nagler and 21mm and 17mm Ethos). The Paracorr 2 has a range of 17.8mm, and accommodates the modern eyepieces with very high focal planes. The Paracorr 1 has 4 lenses, the Paracorr 2 has 5. Both units have the 1.15x magnification primarily to avoid having to in-focus the eyepiece + Paracorr combination too far. A good example is that the Paracorrs require about 14mm of in-travel compared to the eyepieces alone, while the Explore Scientific HRCC requires 32mm of in-travel. Where imaging is concerned, the tunable top is removed and the 2.4" adapter is added to either Paracorr. Achieving focus will be the same with each. At f/5, in imaging, you will not really see a difference between the two Paracorrs if set up properly. Visually, you will see a difference, and most notably with the 3 eyepieces I mention and a few others from other companies.
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