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Piero

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Everything posted by Piero

  1. I have the Lunt / APM HDC 20mm. The field is well controlled up to the edge with very minor astigmatism in the last ~5% of the fov. Honestly, you need to look for it. The lens rubber is particularly comfortable. The eyepiece is quite light (678g) when compared to the Ethos 21 or ES 20mm 100 deg. In general it is a fine eyepiece. Mine does not get much used simply because 1) I prefer eyepieces with a smaller AFOV (I kind of feel lost with 100 deg), and 2) as my telescopes are medium / slow I tend to jump from 30mm to 12.5mm. p.s. Mods might complain the fact that you asked about buying / selling outside the classified. I PM'ed you, but will stick to the rules not to discuss about this here.
  2. Yes, encoders can be very valuable. Sky Safari can go quite close though, with the main difference that it lets you star hop.
  3. I have the S&T pocket star atlas too. For some reason though, I've never really got along with it whether indoor or outdoor. For sure I am a minority because all the comments I've read are very positive. The issues I have are: limited number of stars. Fair enough, it is a pocket star atlas, but on the other hand constellations are often in multiple pages. So it hits neither the detail, nor the broad view how pages are presented. I feel comfortable with pages following a decrease in RA. That's intuitive to me colours. Colours are fine with me indoor, not outdoor That's why I prefer the use of a tablet in the field and a rich star atlas for planning observing sessions indoor. For binoculars or other wide field observing at low power, I prefer a broader atlas than S&T PSA. For instance, the Bright Star Atlas by Tirion and Skiff works better to me. The only drawback of this atlas is that the charts does not have correct angles, which can be an issue particularly in the polar regions.
  4. I've heard of, but never looked through them. How are they? Edit... just found this:
  5. The telescope has consistently been working very well for a while now. Stars don't show traces of astigmatism. Last night I had another nice session. The sky was rather steady and clear, with very low humidity. The telescope cooled with the fan on for about 2h and then collimated with my 2" Glatter laser (without tuBlug). Eyepieces: 30mm APM UFF (large targets), 12.5mm Docter (all targets), Zeiss zoom (all targets). 20mm Lunt was used for the galaxies, but didn't show anything more than the Docter. Lumicon OIII was used for the Eskimo PN. Main targets were: Monoceros: M50, NGC 2264 (Christmas tree cluster), Plaskett's star (giant O-type binary SE of 13 Mon) Leo: Leo triplet, NGC 2903 (W from epsilon Leo) Gemini: M35, NGC 2158 (interesting particularly above 250x), NGC 2129, NGC 2392 (Eskimo PN - what a sight at 400-500x!), Wasat (delta Gem) Cancer: M44 (Beehive) M67 (King Cobra cluster) Canes Venatici: M51 (faint spiral, but no connection due to LP) I must say that I was impressed with all the targets I've seen. The views were really rich in colour and intensity, with "star dust" visible in the background sky. Beautiful.
  6. [A1] If the laser beam strikes outside the centre of the silhouette on the primary mirror, the focuser axis is misaligned. Assuming that this fact is ignored and one completes with the primary mirror alignment, the result would be that the primary mirror axis is "aligned" and the focuser axis is misaligned. To my understanding, this should show something like: In this figure, the focuser seems perfectly "squared" to the secondary mirror, the primary mirror is collimated, but the focuser axial alignment is still off. One could align the focuser axis first. This would make the secondary mirror look like more elliptic. Then the primary mirror can be aligned. Would this be fine? For visual, I would say so. The secondary mirror is clearly oversized and the primary mirror is still fully visible. There are cases where this cannot be sorted so easily though. If this is the case, one could move the secondary mirror slightly away from the primary mirror and collimate the focuser by levelling the small Allen bolts to the right of the focuser. The focuser Allen bolt at the bottom right needs an extra touch. This would allow to move the reflection of the primary mirror towards the centre of the secondary mirror a bit more. [A2] The effect should be the same as with the laser.
  7. Having a budget limit is important, but understanding your interests is even more, I'd say. Let's simplify a bit.. Imaging. This has rather different requirements. Personally, I would keep this as separate. GoTo. Are you interested in GoTo mounts because you don't like star hopping much? A 10" (solid tube) dobson is a noticeable step up from your 6" and a very good all-around. Personally, I would get the "manual" version (=no GoTo) and learn how to move around the sky. I would then add a decent collimator, Sky & Telescope Pocket Sky Atlas, and 3 decent eyepieces to cover 5-4mm, 2mm, and 1mm exit pupils (basically eyepieces with focal lengths of ~25mm, 10mm, and 5mm). I would also get an adjustable chair and an AstroZap dew / light shield. This telescope can still be moved by one person without too much effort and fits in the backseats of a car, if you want to take it out to darker skies. One day you might decide to get a second grab 'n' go telescope like a 80mm F6. This could be used for wide field imaging too if you add a GoTo mounts like a SkyWatcher HEQ5 PRO.
  8. As I've a couple of days off this and next week, I am revising my equipment a bit, which primarily means cleaning up and check that everything is okay. This morning, I took sometime to improve my Baader VIP barlow (now barely recognisable!). In particular, I added the standard ring 2"-to-T2 (which comes with the barlow) at the bottom of the 2" Baader nosepiece. This allows me to use 2" filters at the bottom of the nosepiece and just above this ring (see photos). Some tape was added so that the cap stays in place. This also facilitates the removal of the end component when the filter is added. This can be very handy for planetary nebulae with my Zeiss zoom. With the VIP, the zoom operates in the ranges of 142.20x to 532.74x and 159.13x to 596.16x, with 1x or 2x 15mm spacers respectively.
  9. I had 1.25" Astronomik UHC and OIII filters but these were replaced by 2" DGM NPB and Lumicon OIII. No direct comparison was done between the NPB and the Astronomik UHC. Both are very fine. I prefer the NPB for the reasons stated by John.
  10. Yesterday I received a copy of interstellarum deep sky atlas (IDSA) so that I can visualise the location of the objects described by Burnham in his celestial handbook. I find this approach incredibly useful to learn more about the sky. This wasn't new to me, but when I was doing so, it was with my TV60 which is a bit limited in aperture. With the dobson, it's another story. Looking forward to start off making a good observing list for monoceros, one of my favourite constellation. Outdoor, I prefer a tablet with sky safari to a paper star atlas. The IDSA is a great and powerful tool, but in my opinion it is more suitable indoor for studying the sky. If I really wanted a paper sky atlas for outdoor, I would use Uranometria 2K AFTER a list of targets indoor was created indoor using another atlas. Both atlases complement each other in my opinion. IDSA is great for understanding what is visible and what is not given a certain telescope. The labelling is also great, particularly for double stars. U2K is great because is more readable in the dark as it is black and white and the fonts are reasonably large for all kind of targets. It might also be easier to handle on one's legs if observing in a seated position. Said this, I prefer a tablet with red screens to dim the brightness in the field. To me this is far more practical and allows me to make paths between faint stars, which can be tricky in areas of the sky without bright references.
  11. Good luck with the restoration of this Dobson. Hopefully it will see some light soon!
  12. I also think that it is a good companion to Suiter's. Same for Texereau's how to make a telescope. Same for Burnham's.
  13. I bought a copy of IDSA, in order to map the objects described in Burnham's celestial handbook and create observing lists. The atlas for outdoor work is Sky Safari Pro instead.
  14. Star names - their lore and meaning by R.H. Allen is a classic one. It is mentioned quite a lot by Burnham in his Celestial Handbook, which is another classic. Both are highly recommended.
  15. Sidgwick's Amateur astronomer's book is excellent in my opinion. Very inspirational and rich of insights. A keeper.
  16. Thanks. Burnham cites that book quite often. That's how I became aware of it.
  17. Found in the second hand market:
  18. By 'tipped' do you mean off-axis towards the primary mirror? 1. A primary mirror axial misalignment will cause coma on axis (coma due to misalignment). 2. A focuser axial misalignment will cause the stars to focus at different points across the focal plane. 3. A secondary mirror (severe) misalignment will cause unequal field illumination. It's rather obvious that only the first one degrades on-axis, therefore 2 and 3 reveal nothing on a star testing as this is conducted on-axis. Of the 3, the last one is the less critical for visual astronomy. Without coma corrector, the first one is the most critical. With coma corrector, also the second becomes rather critical. All of them become more critical in faster newtonians. There is nothing to fear in this process. If wrong, it can be fixed and rather easily.
  19. If collimation of a, let's say, f5 Newtonian telescope without coma corrector is checked with a star test, the star must perfectly be on axis, otherwise the coma-dependent misalignment is also visible. This cannot be really distinguished by optical misalignment. So, again, to me at least star testing is not the right way to check collimation as it is too sensitive, unless the seeing is very good, the high power eyepiece is good, coma corrector is used, and the mount tracks automatically. Even so, this test doesn't tell you anything about secondary and focuser alignments. Coming back to the topic, my HG laser and Catseye telecat give the same reading consistently.
  20. Not sure what some members above meant by star testing in this thread. Do they mean "checking" or "collimating" with a star test? In my opinion, I wouldn't suggest the latter, particularly with manual driven mounts. Regarding the former, the procedure can be rather complex as it is easy to get errors due to other factors which don't have anything to do with misalignment. Of course, if one knows how to star test, the feedback given by this tool is incredibly useful in order to understand what does not work properly in a telescope. Regarding the importance of collimation, well Suiter's book on star testing offers some quantitative data on this subject. Of course, a slightly miscollimated telescope still works. Said this, if one pays for premium optics and is happy to have an "okay-ish" collimation, the same person should reflect that some okay-ish optics with excellent collimation could probably give the same results in terms of view quality.
  21. Withdrawn. Feel free to archive this advert.
  22. I tend to stand while observing as that's my preferred way. This with both my dobson and refractors. The refractor mounts have an extensible column which I love as it avoids contortionism or "yoga postures".
  23. Last Thursday night the seeing was great with very good transparency. Observing Aristarchus crater and plateau from 160x to 630x was amazing. In particular, I was impressed by the kind of "river" approaching the crater to the left and how the light played fantastic shades inside. From Wikipedia: Aristarchus plateau (NASA).
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