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Piero

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Everything posted by Piero

  1. Thanks Stu, that's a very interesting article. I wasn't aware of it.
  2. Yes, that is the one. See: https://www.firstlightoptics.com/howie-glatter-collimation-tools/howie-glatter-single-beam-2-inch-laser.html There are other attachments for more exotic collimations, but the 1mm is the one you need really. I have the 650nm version which is fine for collimation in the night. You can use the 635nm which is fine for day time collimation, or night time using a brightness reducer.
  3. The HG's a great laser collimator. Congratulations! I use mine with the 1mm attachment. I also have the tublug but only use it when feeling lazy.
  4. After 3 pages, it seems to me that this thread hasn't gone anywhere.. It is a shame because it would have been interesting to read about a star testing-based quantitative comparison between these two instruments. Oh well..
  5. I would recommend a 8" f6 Dobson as an all-around telescope. The skywatcher version is good and rather cheap, but if you can stretch it a bit, the Bresser version is mechanically much better. Orion optics UK... I would only consider it in the second hand market. Even then, I would probably go for something else.
  6. By the way, here is the 3" big paracorr "beast".
  7. My minimalistic 2" set. As I am moving fast, a paracorr2 was added a few months ago. Flo sent me the 3" version (that's a beast!) by mistake, but then all was sorted. It might be that I will let go the tublug at some point as I collimate with the laser only. Thoughts for the future. Left to right: Zeiss zoom, APM UFF 30mm, Docter, 2" HG laser 650nm + tublug. The VIP barlow is above the Docter. I use it with 0mm, 15mm, or 40mm spacers. The two boxes include 2" Lumicon OIII and 2" NPB filters
  8. @johninderby Are you still interested in this product? If so, we could split the cost. Let me know. Piero
  9. Coma is an aberration present in telescopes using paraboloid mirrors. It is not present in modern / half decent eyepieces. An F4 Newtonian has a coma free linear radius of 0.022*4^3 = 1.408mm . This defines the area in which the Strehl of a perfect mirror is 0.80 or better.. Also, variations of the mentioned formula generally use a more stringent factor than 0.022. Considering a field stop of 27mm for the 24mm TV Panoptic, coma is expected to be present and easily detectable in an F4 newtonian telescope. Also, the fact that Televue eyepieces are highly corrected to the edge, will make the dete
  10. In `Observational Astronomy for Amateurs` Sidgwick mentioned magnifications of at least 400x for critical lunar observing. Assuming crisps views, his comment can offer an idea of what kind of minimal aperture he meant! Again, I think we all have different tastes on this. At mags over 400x, one can seriously study the moon for years, due to the small image scale. Said this, some of the very best views of the moon I had were when it was full, slightly above the horizon, and using my TV-60 at 15x. In particular, the Moon was coming up from bushes and tree branches with a bird or two crossing
  11. Binoviewing with two docters is a rather expensive experience.. I don't binoview though. I compared my docter against a Delos 12mm and I preferred the former one. You can find that thread on CN forum. So, for me it does justify the cost. Besides, I bought mine in the second hand market from a member of this forum. Anyway, I don't have many eyepieces as a large set doesn't fit with my way of observing. For others, it is the opposite and owning an eyepiece between two magnifications (or FOVs) is important. For others, 100 deg afov eyepieces are cool, for me they are a dis
  12. My favourite eyepiece is the 12.5mm Docter UWA. Combined with my modified Baader VIP barlow I get an equivalent ~7mm or ~5mm, depending on target and mood. Another eyepiece I love and use quite a lot is the 30mm APM UFF.
  13. I think it all depends on the kind of objects one wants to observe. With my TV-60, I've spotted/observed about 250-300 targets. I intentionally wrote spotted/observed, because a few of those targets can only be spotted on that telescope given the limited aperture. Said this, it has been a great learning curve. In contrast to a larger telescope, a small wide field refractor can let one find many objects, which means the knowledge of the sky increases considerably. There are so many classes of objects that that telescope doesn't / cannot show well though. My 100mm Tak is a bit better
  14. Indoor, I enjoy using Interstellarium and Bright Star Atlas 2000.0 . Outdoor, I generally use SkySafari Pro or Stellarium apps on a tablet. The only "paper" tool I use in the field are the Herschel 400 guides by Alvin Huey (see: http://www.faintfuzzies.com/DownloadableObservingGuides2.html, but a printed copy can be purchased and delivered at home) . When using these guides, I focus on one single constellation for the whole session.
  15. Sure and sorry for the delay Heather Teeter's light shrouds are excellent in my opinion. Mine improved the telescope a lot!
  16. The main reason for detecting astigmatism at high magnification (e.g. <=1mm exit pupil) is because any potential astigmatism present in the eye is minimised or even absent. An observer's astigmatism must be really severe to show effects at high power. In general, most of the eye imperfections are off axis of the pupil. Reducing the exit pupil, reduces the use of that part of the pupil. On the other hand, any astigmatism in the telescope is still present, whether at high or low magnification. Of course, one could also discriminate eye astigmatism against telescope astigmatism at low ma
  17. Yes, I remember your thread. It is among my browser bookmarks!
  18. Yes, you can do that. You could install a metal bar on the that mirror wood panel to provide a support for the two shafts where the sling cable can be installed. On a 12" mirror, a 1/16" cable is fine. The difficulty is that you need to make sure that the height of the sling cable is at the COG of the mirror. The bearings in the Howie Glatter's design are there for this reason and because they are installed on the mirror cell of a Kriege's design, which is different from the David's design. Here is a tool for calculating the mirror COG: https://www.cruxis.com/scope/mirroredge
  19. BTW, I now use this dobson with a TV paracorr2. Despite the fact that a few people suggest the requirement of a coma corrector on sub F4.5 Newtonians only, I can say that I do notice an improvement in the views of this F6 telescope. Even more.. if one wants refractor-like views with a Newtonian telescope (AND I DO!), a coma corrector is needed, IMHO..!
  20. Not necessarily. I've tested this quite a lot and I am more and more convinced that what really matters is the symmetry (or almost) of the air flow around the mirror. In you astrosystems dobsons, there is a low opening on the bottom front and two circular openings at the bottom back. To me, the purpose of those two holes is to balance the air flow of the opening at the bottom front of the mirror box... In Kriege open design, the symmetry is present by definition John Dobson's design was fully closed, preserving the symmetry of the air flow. In David's design, this symm
  21. Just to clarify, David Lukehurst installed a sling cable which is not the Glatter's design. David's sling works ONLY IF it is installed on the same plane of the mirror and if the cable is mounted parallel to the COG of the mirror. If these conditions are not satisfied, astigmatism will be visible. In the telescope in that thread, the first condition was present, whereas the second was not (the cable was placed at half mirror height..). I reached the second condition by changing the back mirror supports, effectively raising the mirror height as much as necessary. The other issue tha
  22. I use 300-500x quite regularly after optimising my dobson and 150-370x with my refractor, so I cannot agree with the statements above.
  23. To me most of the time, the "atmosphere" 1 inch on and above the mirror related to improper cooling, uneven mirror temperature in general, poor mechanics (e.g. mirror back and lateral support, the way the secondary mirror is mounted, the way the focuser drawtube moves, etc), often so and so optics, and poor collimation are at the basis of limited magnifications in larger telescopes, rather than the actual atmosphere. To the OP. That's a great project. One warning though as you mentioned finances. Even if you make the whole thing, including the mirrors, the overall cost will still be notic
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