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About Piero

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    Brown Dwarf

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  • Interests
    Amateur astronomy, bioinformatics, software engineering, mathematics, languages.
  • Location
    Cambridge, UK
  1. Globulars and galaxies

    Really enjoyable reading and great shots, Gavin! Thanks for sharing! It is cloudy and snowing over here, but glad to know that the sky was clear in some part of the UK and you got a chance to have a great session.
  2. Planning your ideal eyepiece collection

    You might find useful the comparison between nebula filters by Dave Knisely: http://www.prairieastronomyclub.org/filter-performance-comparisons-for-some-common-nebulae/ He really knows what he's talking about. Personally, I'd go for the Lumicon UHC and (old) OIII. The NPB is close to the Lumicon UHC as far as the central region concerns. The Baader OIII is too tight and cuts off 1 OIII line. Because of this, I would not buy one for visual work, although it might be suitable for imaging. The astronomik UHC and OIII until 2 years ago at least pass some nm more than necessary compared to the lumicons. Of course, they would still work, but the Lumicon can show some more contrast. The worst filter is light pollution. Unfortunately, this is very effective at ruining nebulae details!
  3. Planning your ideal eyepiece collection

    Are these smiles enough?
  4. Planning your ideal eyepiece collection

    I had astronomic UHC and OIII filters, but prefer the NPB to them. Maybe it's just me.
  5. Planning your ideal eyepiece collection

    Well, I agree with all that was said above. Lunt 20mm, 9mm, and maybe a 5mm at some point, as suggested by Iain. In any case, you could get the 20mm first and see whether you like it. Regarding filters, if you find a shop still selling the old Lumicon OIII (the good one having the tight passing band), go for it. Alternatively, another very good filter, which is slightly less specific than the Lumicon OIII, is the DGM NPB. You can get one from okularum.eu in Denmark (see: https://okularum.eu/DGM_NPB_filter-2 ). I bought from them a few items including my Vixen HR. Really good guys and a pleasure to deal with. The NPB is a kind of in between a Lumicon UHC and OIII, but transmits some reds which can be nice on some extended nebulae. The side effect of the NPB filter is the green and red colours in stars are overlapping. Some people dislike this, others don't. Personally, when using a nebula filter, I consider stars just as orientation checkpoints, so I don't really bother how they look like. M42 is outstanding with the NPB filter in my opinion.
  6. Planning your ideal eyepiece collection

    Don, who is also a member here on SGL ( @Don Pensack ), explains this very well in my opinion: https://www.cloudynights.com/topic/565194-focal-ratio-and-coma/page-3#entry7710217
  7. Planning your ideal eyepiece collection

    Your statement is misleading. >>> most 2 inch eps are longish to long FL, & have wide FOV. This is generally true. >>> Therefore coma will be more likely in a fast mirror. This is true. >>> [fast mirror], which will generally affect views through 2 inch diameter eps. This is incorrect. Most of TV Naglers and Ethos have 1.25" barrels, and will show more coma than 2" MV 30mm / 40mm, 2" Panoptic 41mm / 35mm / 27mm, etc. The only thing revealing more coma is the telescope focal ratio: the shorter the focal ratio, the smaller the coma-free area. In a fast telescope, this coma-free area is sufficiently smaller than the whole FOV of the eyepiece, making the detection of coma rather obvious. The typical formula calculating the coma-free area is 0.01778mm x f/ratio^3 . Barrel size has nothing to do with coma, so implicating coma from this, is misleading. Regarding LittleGuy's F4.7 telescope, this means that the coma-free area in his telescope is just ~1.85mm. Rather small... said this, before investing in a CC, it is important to observe and see whether this really compromising the views according to one's eye or not.
  8. Planning your ideal eyepiece collection

    As far as I read from Ludes' comments, APM telescope is taking over the production of Lunt XWA / HDC. Not casually, the 13mm is advertised as APM telescopes and not Lunt. ES, Lunt/APM, Myriam, WO are clones of the TV Ethos. Said this, the Lunt series introduces some valid improvements, like substantial reduction in weight (e.g. the 20mm weights just 667g) and different and effective eyecup. The 20mm Lunt goes deeper than the Panoptics I've tried as is at least on par with the Delos I had, in terms of on axis contrast. It also reveals a vibrant colour tone on stars, which is not something I expected at that extent. I've read a few times that the ES 100 line is a bit like the TV Naglers on steroids. Well, to me, the 20mm Lunt is better on axis than the Naglers T6 I had and looses nothing at the edge.
  9. Planning your ideal eyepiece collection

    From your post, it seems that you are suggesting that coma depends on the AFOV and the barrel type, hence the field stop. If so, the latter is incorrect. Take two 100 deg eyepieces with focal lengths of 20mm and 10mm. The FOV diameter in the 10mm is half the FOV diameter in the 20mm. Therefore, one would be tempted to say that it "shows" half coma. However, the magnification is double (and double is the coma aberration), therefore the amount of visible coma is exactly the same between the two eyepieces.
  10. Planning your ideal eyepiece collection

    Those targets require dark skies. These are more important than any eyepiece as far as faint light catching concerns. Personally, I'd start with something that I use most of the time, and with time it will appear clear if more dedicated eyepieces are needed. Gerry lives in one of the darkest place on the planet, is very experienced on a multitude of targets, and observes with top-notch equipment.
  11. Planning your ideal eyepiece collection

    Yes, sure, take your time. Most people like 100 deg eps, but not everyone. Regarding the comparison against the BST, I believe the Lunt is better. My 20 Lunt is certainly on par with the last offers by TV regarding contrast on axis, and I have nothing to complain with its off axis performance. The eyecup is a dream. I wish many other eyepieces had an eyecup like that. I placed a magnetic bar on the bottom side of the tube. No balancing issue. Compared to the other 20mm 100 deg, the 20 Lunt is a feather, which is also a great advantage. I will take a pic of the Lunt with the refractor at some point ...
  12. Planning your ideal eyepiece collection

    Hi Neil, as said by other members the 20 HDC is very good both optically and ergonomically. Also, the eyecup is an improvement against TV eyepieces in my opinion. I had the 30 ES which was sold because the 20 HDC was used more, is optically better (the 30 ES is a good eyepiece don't get me wrong), and is considerably lighter. This was with an F6 dobson. With a F4.7 dobson I would go straight with the 20 HDC, as Mark suggested. Again, as Mark suggested, I'd also advise to get the 20 HDC first. With a F4.7 dobson, I would get a 9 HDC afterwards (assuming that you like 100 deg views) rather than the 13mm, simply because the latter will give you almost 2mm exit pupil. With these eyepieces, I would forget a 2" barlow / powermate. Anyway, the 20 HDC is really a great eyepiece. It's also a pleasure to use in my refractor, showing nearly the whole Orion's belt in the FOV. The background sky in both my dob and refractor is neutrally dark (like TV eps), not grey as some eyepiece I have tried. The edge is also clean, allowing you to see the telescope coma (a bit noticeable at the edge in <=F6 scopes, but not disturbing). I am not obsessed with 100 deg views, but this is a very fine eyepiece. If I didn't have the Docter and the Zeiss zoom to play with, I would probably get some other focal length..
  13. Takahashi 32mm Abbe MC

    Never tried one, but I read (https://www.cloudynights.com/topic/474675-the-takahashi-abbe-ortho-a-brief-summary/), that it is a good eyepiece.
  14. Jupiter, GIF 1-2018

    That's a very impressive work!