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Piero

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Everything posted by Piero

  1. John, I don't think there are things like perfect views, optics, or mechanics, but just things that either work bad or within an acceptable tolerance. I am critical with my equipment because certain things can be improved. Others will just need to be accepted as they are. It is just a matter of recognising them. I see this as a continuous learning process. Your comment pushed me to test that combination again. So, thank you for your feedback. This didn't change my opinion on that eyepiece, but the additional test let me understand the eyepiece and the refractor a bit more, which is
  2. I found this annotated image from this thread: https://www.cloudynights.com/topic/523392-replacement-focuser-for-sw-ed80/ It contains some good advice. Could it be that your focuser misalignment was due to heavy load?
  3. Nice post, Gerry! It made me smile! Next time then! It will still be there tomorrow.
  4. I apologise with the OP as this post is a bit off-topic. Citing from the link above "Most refractors have little or no coma, contributing to their being well-suited to wide-field viewing and imaging." This doesn't exclude coma in refractors. In addition, coma can be related to the telescope optical design (e.g. Newtonian telescope), but also induced by misalignments (miscollimated axes). If the focuser of a refractor is not collimated, the telescope can show coma, even on axis. My second comment above came from notes I took about 2 years ago when I bought the Takaha
  5. Fast optics show coma, whether refractor or reflector. The Televue 100 refractor doesn't because it has lenses in place to correct coma.
  6. In my f7.4 Tak refractor, I can see it at the edge with my Lunt 20mm 100 Deg.. not disturbing, but it's there. In a f5 or f5.3, coma is certainly visible. Of course it's up to the telescope owner to decide whether it is bothersome and / or to do something about it. Consider a dim star on axis. On fast optics without coma corrector, that star can become invisible at the edge due to the fact that it's light is spread on a larger area. This doesn't mean that you don't have coma. Same for seeing colour on a star off axis. Rather than chromatic aberration, that is more likely due t
  7. Well, beyond approx 25 Deg AFOV, coma is visible in a F5 telescope. Not that it isn't visible within, it's just that beyond 25 deg the diffraction disk becomes larger than what it should be with the diffraction limited optics.
  8. Keep in mind that some of the Allen screws are for regulating the tension of the focuser - making smoother or firmer. What you will need is to adjust the drawtube axis instead.
  9. Thanks. I need to do some research as I don't have that telescope. From preliminary search, it seems that the focuser can be collimated. https://www.cloudynights.com/topic/140083-sky-watcher-100ed-collimation/ Check jrbarnett's comment. I'll have a proper look at this this weekend.
  10. I think it could lose a tiny bit on axis, but the improvement across the field should be huge at f4. You will have the whole field within diffraction limited threshold. The increase in magnification could also help you spot some other faints..
  11. Curious to know how you will find it, Gerry.
  12. Good to hear that! Anyway, I would also suggest to rack out the drawtube as when a normal eyepiece is in focus. A fully retracted or extended drawtube is not in a good position to check the focuser collimation, as this can be quite different. Also, why should this be done with the telescope pointing to the floor or ceiling? The laser is expected to be quite aligned in those positions and does not stress the focuser off axis. Focuser collimation with a refractor should be done with the tube put horizontally (and drawtube as said above). With your template, you can check that the
  13. I am not sure you can rely on the mirror on the floor. The returning beam will depend on the angle of that mirror. If the beam goes through the hole of your template, which is supposed to be at the centre, that's a good indication that the focuser is collimated. In any case the tolerance for the focuser axial alignment is 0.03xD, where D is the aperture and here no coma corrector is used. That is 3mm for a 100mm refractor. For checking collimation of the lens, see Suiters' book.
  14. Whilst it is true that a miscollimated telescope can show astigmatism, in this specific case astigmatism dominates over coma when the strehl is below the diffraction limited threshold (about 0.80). At that point the images are quite bad. If your focuser is miscollimated, you should detect coma on axis. That is the predominant aberration. If you are certain you see astigmatism, it could be in the eyepiece or the optics are retained too tightly. Also, make sure the telescope has cooled down properly. For test collimation I use the Glatter square attachment with my Glatter's laser.
  15. Mm.. some interesting feedback from this conversation. Thank you all. Food for thought!
  16. In an ideal world, I would love a Vixen HR 5mm, but it seems this cannot be made due to the inherent design of the HR line. So, options are: - 11mm +/- 2.25x barlow - 5mm and use the 24 Pan +/- 2.25x Barlow Yeah.. a Pentax XO 5mm would be great! ... So would be the XO plus the 10mm ZAOII... Tough to find them and on the wallet though..
  17. I currently have a Nikon MC1 zoom 21-9mm which works well although I had to re-do its barrel as it is a spotting scope eyepiece. In terms of optical quality it matched my Vixen SLVs.
  18. Thank you all. From your comments, it reminds me of the Orion super Plossl Sirius 10mm I bought back in the nineties. Good eyepiece, but tight on eye relief.
  19. I am considering this eyepiece for my refractors. It would be used with and without Baader barlow 2.25x. Has anybody tried this combo? In the past I tried the BCO 10mm, but I let it go.
  20. Under my skies, I enjoy 5mm exit pupil. I've tried more, but I found that 5-5.5mm is about the largest I would use.
  21. @BGazing Thank you for the info. I was not aware of the ADC, and it seems interesting. Will certainly study it a bit more. For the time being, I decide to postpone the purchase of a coma corrector. After removing the sling due to its incorrect installation which caused a massive amount of astigmatism (it squeezed the mirror because it passed through the mirror edge supports and also the wrong installation did not allow it to remain parallel to the mirror plane), I noticed that there was still some astigmatism, this time due to the mirror edge supports which tightened the mirror too
  22. I bought two of these collimators, one for my dobson in Italy and one for my dobson in the UK. Not travelling much to Italy as I expected, I have decided to sell one. This is a rare opportunity as these collimators are keepers. Frankly, I've never seen one in the second hand market. This is in perfect conditions, no mark at all as it was used only in my Moonlite CR2 focuser which has a compression ring. The internal of the battery is immaculate (see photos). The Howie Glatter's collimator is the best laser in the market and comes with 1mm aperture stop attachment. This versio
  23. The Vixen 42 LVW I had was probably good in a F9 or F10 telescope, but in my Tak f7.4 showed quite a lot of astigmatism in the last 20% of the fov. The Meade maxvision 40mm is another good eyepiece after removing its armour. In any case an eyepiece giving 7mm exit pupil is very specialised and requires deep skies. In my 'long focal length' journey the TV panoptic 35mm was much better than the above two eyepieces. It was replaced by the APM UFF 30mm which gave me a more useful exit pupil and its weight is closer to my other eyepieces.
  24. I have never used that collimator so, cannot comment. It's a 1.25” model, so it's fine if you use 1.25" eyepieces. If you use 2" eyepieces, you should make sure that your 2-to-1.25 reducer does not affect the focuser axial alignment. Examples of reducers that do not affect the alignment are the Baader clicklock and the Glatter's reducer.
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