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Don Pensack

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Everything posted by Don Pensack

  1. Try a 30mm APM UltraFlat field eyepiece to round out the set. Then your training will be complete.
  2. For low power, a 30mm APM UltraFlat Field eyepiece is a winner. It's lighter and smaller and as sharp as the 31mm Nagler and 30mm Pentax XW, with which it competes. And compatible with glasses. The next one needed is something like the 17.5 Morpheus. Wider, which befits a higher power, and also compatible with glasses. If you don't need glasses, the TeleVue Nagler Type 6 eyepieces could round out the higher powers (down to a 3.5mm eyepiece). The APM 100s are a good value, too, and the shortest focal lengths are the best-corrected, I've found. It makes sense to go wider in apparent field as the magnification goes up, to keep the field from shrinking too much. Especially in an undriven dob, where things can go whizzing through the field and a wider eyepiece gives you more time between nudges. Russ, though the Morpheus can be used as 2" eyepieces, you should think of them as 1.25", because if used as 2", they require an enormous amount of out-travel at the focuser. They are closer to parfocal with a lot of other eyepieces if used as 1.25". There is no harm in using them that way. All the eyepieces I've mentioned except the 30mm APM can be used as 1.25" eyepieces.
  3. The primary thing to do in an urban LP environment is use a bit higher powers than normally used at a dark site. Yes, this will dim the object as well as the background, but the larger size and darker background will make most extended objects a bit easier to see. For any star or star cluster (open, globular), higher power yields improved contrast and allows you to see fainter stars. Many if not most beginners use too low a magnification for most objects and that's OK in dark skies, even though they'd see more at higher power. With most DSOs (not the largest objects) observed in an urban setting, you probably shouldn't go lower in power to view them than 0.5D in millimeters, i.e. a 10" scope at 127x, or a 6" scope at 76x. The lower powers can be quite nice, but not particularly when the skies are light-polluted.
  4. I seem to recall some early Questars, Bushnells, and even a Celestron with threaded-in eyepieces. But I haven't seen one since the '80s.
  5. Just posted the 2020 Eyepiece Buyer's Guide https://www.cloudynights.com/topic/700069-2020-eyepieces-buyers-guide/ Enjoy.
  6. Sorry, just saw your question. The Paracorr's top is not smooth enough to be used for fine focusing. What you do is focus with it (after setting the Paracorr with an eyepiece that you know the setting for and focusing the scope) when you insert eyepiece B just to find out what the proper setting is for eyepiece B. Write it down. Next time, before inserting that eyepiece, dial the top to the setting you discovered, then insert the eyepiece. It'll be really close to focus and only a tiny touch up of the fine focus knob will be necessary to achieve pinpoint focus. Even with knowing the settings for every eyepiece in your collection, you will still need about a 1mm range of focus in your focuser. As for figuring out what eyepiece to start with, if you own a Paracorr 1, you should not use a 31mm Nagler, or 21mm or 17mm Ethos or a 20mm ES 100° as your starter eyepiece, as these do not have optimum settings in the range of the tunable top. Use another eyepiece you know the setting for. The eyepieces I mention will all use Setting 5 (all the way down on the Paracorr 1 ), but that setting is still a tad short of optimum. Because they are not at the optimum position relative to the CC lens, if you focused using the tunable top on another eyepiece, it, too, would be at the wrong position for optimum correction. So, an 8mm Delos uses the Paracorr 1.25" included adapter and the 14mm and 17.3mm use the in-travel adapter to make them parfocal with the 12mm and shorter Delos, all of which are parfocal.
  7. The visibility of coma is apparent field related, i.e. you WILL see significant coma in a 13mm 100°, whereas it will be substantially less in a 72° field eyepiece. I don't really understand why you don't use the Paracorr for all your eyepieces as it not only eliminates coma but also slightly flattens the field. The 13 APM has a small amount of induced astigmatism at f/5 which will be worse at f/4. The Delos will have a far better edge, where star images are concerned. As for not fiddling around with Paracorr settings, perhaps you aren't aware you needn't do that. The Paracorr will parfocalize all eyepieces, i.e. simply insert eyepiece B after eyepiece A is properly set in the Paracorr, and focus eyepiece B using the Paracorr's top. The setting that results in focus is the setting for that eyepiece. That's no more complicated than moving the focuser. Even if you insert a 1.25" adapter, the process is the same. You may still need to fine focus with the focuser, but a half millimeter of focus travel is about all you'll need. The 14mm Delos, however, will need the TeleVue In-travel adapter (AIT) to be parfocal with the 8mm Delos when the 8mm Delos is used with the Paracorr adapter.
  8. Add the additional eyeguard extender. That will solve your problem.
  9. From hours in the field: Mars: Contrast Booster stupendous--simply the best Mars filter out there. Jupiter--Moon and Sky glow filter better, though CB helps a little. Best is no filter and high power. Saturn--Yellow #12 or #15 enhances shadow details in rings. Otherwise, like Jupiter--high powers with no filter is best. M&SG not much help at all.
  10. Some possibilities compatible with glasses: Baader: Hyperions, Morpheuses Explore Scientific: 30x82, 28-40x68, 12-17x92, 26-40x62, 30-40x52 TeleVue: Delites, Deloses, 32-55 Plössl, Apollo 11, 27-41 Panoptics, 22-31 Naglers, 17 Nagler marginal (a bit tight) Olivon (BST or Barsta): 70° Series, 58° series (marginal--a bit tight) Pentax: XWs, XFs APM: 12.5x84, 24x65, 30x70 Vixen: 2.5-25 SLV There are others, but that gives you some choices.
  11. Since you can have an exit pupil larger than your pupil in a refractor (it only sacrifices some light, but the magnification is really low), I've tried a 55mm Plössl in my 4" refractor and got to 13x and a field of 3.7°. It's not quite large enough a field for using the scope itself as a finder (my finder is 8x and a 6° field), and the magnification is barely more than my finder, albeit with a significant jump in aperture. "Context" views for objects like the Pleiades or M31 do require massive fields of view. My best view of those objects with context is something that yields ~10-20x and a 4.5° field, like a 31mm Nagler in a TeleVue NP101 refractor. I've regretted selling mine for several years.
  12. For me, yes, 44x is low enough as a low power. I don't need for my refractor to duplicate a binoculars power or field size. IF you seek a really wide field and really low power, then perhaps it makes sense, but I really see very little reason even then to have a magnification below about 5X/inch (5mm exit pupil) That would be a 23mm eyepiece. Yes, the image is brighter at low power, but star clusters will be poorly resolved, and galaxies really small so unless you really enjoy the "context" view, I wouldn't bother. The largest eyepiece I use with my 4" refractor is an 18.2mm yielding 39x. My most-used eyepiece is an 11mm (65x) or a 7mm (102x).
  13. I used a #30 magenta on Mars for a while, but a friend suggested the Baader Contrast Booster. it is simply the most amazing Mars filter I've ever used, and I've had about 9 other specialized Mars filters over the years, including the TeleVue Mars A and Mars B, the TeleVue Planetary filter, the Orion Mars filter and the Sirius Optics Mars filter, a #23a, a #25, a #21, and the #30 magenta. None gave the incredible images of the CB. If you have one, try it on Mars. You'll be amazed.
  14. Except the UHC. Astronomik's UHC filter passes the H-α wavelength at a high percentage, whereas TeleVue's Nebustar II (their version of the UHC) has no red transmission at all. Star images in the Astronomik have a bit of red tint to them, where the stars in the TeleVue are the usual blue green seen in a filter lacking red transmission. The current Lumicon Gen.3 UHC has the same profile as the TeleVue, while the DGM admits a much broader patch of red than the Astronomik.
  15. The 11mm was the poorest selling Nagler, maybe the same as the 2.5mm (also discontinued). Everyone who bought the 13mm skipped to the 9mm as the next size. The Apollo 11 eyepiece was designed to commemorate the moon landing of the LEM of the Apollo 11 mission. So of course it had to be 11mm. It almost missed the 50th anniversary year because of some changes after the prototypes. The Nagler wasn't discontinued because of the Apollo 11 eyepiece, but because of sales. And if TeleVue came out with a long eye relief line of T7 Naglers, I'd suggest they skip 11mm.
  16. My astigmatism has gotten worse over the years. At first, no visible astigmatism at 6mm exit pupil, then 4mm, then 2mm. But the eyepieces I use under the 2mm exit pupil are so good, I don't intend to part with them until forced to do so by Mother Nature. You can plan for getting worse, I suppose, and just get only eyepieces compatible with glasses all the way down to the smallest focal length. I can see that, but I'd hate to give up 100-120° fields, especially at high power in an undriven dob.
  17. Though it's excellent, I'll never get my investment back. Only my heirs will appreciate it, perhaps. But in the meantime, I have something that brings back a lot of memories and yields pretty darn good images in my scope in a form I can use my glasses with. I compared it to the 12.5 Morpheus, 10 Ethos and a couple of others. If you don't need glasses at that focal length, my advice is for the 10 Ethos. And if you don't need the large field, the 10 Delos. There just aren't any long eye relief ultrawide 10-11mm focal length eyepieces that can bring back memories like this one does. It's ridiculously expensive, and, in a few years, you may be able to buy a used one for less.
  18. Baader Hyperion, Baader Morpheus, Explore Scientific 92° series, Explore Scientific 28,34,40 x 68°, ES 26,32, 40 x 62°, ES 30, 40 x 52°, TeleVue Nagler 31, Delos eyepieces, Delite eyepieces, Nagler 22, Olivon 70° series, Olivon 58° series, Vixen SLV, Pentax XW, APM UFF in 24mm and 30mm Boiling it down to the 5-15mm range, 2 Hyperions, 4 Morpheus, 7 Delos, 8 Delites, 3 Olivon 70, 6 Olivon 58s, 5 Pentax XW, 2 Pentax XF, 8 Vixen SLV = 45 eyepieces in your range, and that's not all of them, merely the ones I can remember off the top of my head. But, bear in mind you may not need glasses below a certain exit pupil. I use glasses from 11mm up and no glasses for 10mm down. You may not require glasses for your shortest focal lengths.
  19. Here is a site with tests of many filters. You can also overlay any filter graphs on top of one another. https://searchlight.semrock.com/?sid=a08a1af9-84ee-49d2-959d-153d7e7c0eb8#
  20. daylight review: https://www.cloudynights.com/topic/687544-televue-apollo-11-reviews-here/?p=9867782 Nighttime review: https://www.cloudynights.com/topic/687544-televue-apollo-11-reviews-here/?p=10009894 There are other reviews in that same thread.
  21. Piero, I did not check the Paracorr setting for the 30mm APM UFF eyepiece because you find its setting the same way you find the setting using the ES HRCC: You use an eyepiece, any eyepiece, that you know the Paracorr setting for, insert the eyepiece, dial in the correct setting, focus the scope and lock the focuser (figuratively, i.e. don't move it). Insert the new eyepiece and focus using the tunable top. The setting that results is the correct setting for that eyepiece. So since I had been using a TeleVue eyepiece prior to using the 30mm APM, i simply inserted the eyepiece and focused with the tunable top. I didn't even bother to look at what the setting was since coma correction was perfect and stars at the edge were tiny pinpoints. Every time someone asks me what the Paracorr setting is for eyepiece X, I just ask if they have one eyepiece they know the correct setting for. If they do, they know the setting for every eyepiece because the tunable top parfocalizes all eyepieces that focus within the range of the tunable tops adjustment (0.7"). Just focus using the tunable top. Now, that won't give you extremely fine focus, which is why you still need to have a millimeter travel in the focuser.
  22. Re: a comparison of distortion characteristics between the 30mm APM UFF and the 30mm Pentax XW: The XW has a very small amount of positive angular magnification distortion, so is like most astronomical eyepieces. The APM UFF has a very small amount of negative angular magnification distortion, so is a little more unusual (far from unique). Both, however, have been designed to control AMD tightly, so both show pincushion rectilinear distortion in daylight use. It's obvious both were designed for astronomy use, as opposed to daytime use in spotting scopes.
  23. +1 for the 30mm APM UFF in my f/5 scope. I have to use glasses at this exit pupil, but correction is excellent and glasses were usable with the eyecup folded down. It was just a little sharper and had slightly better contrast than the 30mm XW in the outer 10° of field. I rated it equal to the 31mm Nagler except for apparent field. It is NOT compatible with a TeleVue DioptRx, so if you need astigmatism correction, you'll need to use glasses or contacts.
  24. Read this: https://www.handprint.com/ASTRO/ae1.html And the 4 parts that follow. You will understand a lot more than the basics by you reach part 3 or 4.
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