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    SGL 2017 SP

Peter Drew

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About Peter Drew

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    Astronomy Centre Todmorden U.K.
  1. I think some "super" Plossls had an extra lens installed to give a slightly wider field of view. Due to the design, even a "standard" 20mm Plossl will give a wider apparent field of view than your 40mm. You could Barlow your 40mm to provide a 20mm focal length.
  2. Close, but not close enough for a 12" SCT in my view. The secondary obstruction shadow is slightly displaced towards the right of the image. Collimation is best done with a small amount of defocusing. I have had better success with collimating on a planet as the disc is less affected by seeing than a star. With a slight defocus a planet will start to develop a ghost image round it, the concentricity of this ghost image is a measure of the accuracy. Worth a try.
  3. I wouldn't want the telescope my car's value would match.
  4. After a while it dawns on you how relatively cheap commercial mirrors are. Nothing like the interest and satisfaction of making your own though.
  5. I'm always advocating the use of rubber bands to relieve the weight of accessories on the focusing mount. It works well, is easy to do and cheap!
  6. Hello Lars. A good plan to mount the binocular well, it makes all the difference. If you eventually go for the parallelogram mount consider reversing it as shown in your diagram. This places the counterweight at the top and the binocular at the bottom. This way you can sit behind/underneath the binocular without the pier getting in the way.
  7. I wouldn't do anything drastic as a first attempt to clean it. Try some warm water with a drop of washing up liquid applied to the surface with just the weight of a cooton wool ball soaked in the water.
  8. Its ages since I last saw a N&Z refractor, mostly smaller than the one shown. I've no idea as to the value but would expect one to be on a par with other famous makes of the period.
  9. I have no experience of these observatories but I have built many from 2m to 9m and the first thing I would say is that observatories are never too big, only too small.
  10. Nice one Olly. Your report, coming from a confirmed "sceptic" nicely endorses this particular telescope, Alan would have been delighted. The optics of recent SCT's seem to be well sorted in manufacture and reliable in performance, however the good performance is fragile, it doesn't take much in the way of collimation error or unsuitable seeing conditions to let them down. Fortunately, collimation is easy and good seeing is just a matter of patience.
  11. Thanks Peter. Then based on my previous comments I still suspect some form of temperature problem. Before we fitted a heater band to remove dew from the corrector we used a hair drier, this of course warmed the corrector and for 10 minutes or so afterwards the star images were somewhat like yours. I also think it worth checking that the corrector retaining screws are not too tight as already suggested but I would have thought that a pre-delivery check at the factory would have revealed this. Clutching at straws now but being as it was a new OTA they are usually shipped with the mirror lock on, has this been released fully?
  12. I don't claim to be an optical expert but I do have considerable experience as a user and former dealer with SCT's. I find it hard to believe that a recent Meade 16" would have significant optical errors. They are their flagship aperture and cost enough to ensure a good quality. The manufacture of Schmidt-Cassegrain optics is well established and reliable, there is little opportunity for errors. Is the OTA new or used, if used it would be good to know its history.
  13. @peter We actually never use the fans!, one 16" is in a 9metre dome and the other in a 3metre dome, they are usually at or around ambient temperature and good to go at the outset. Always difficult to tell whether any subsequent improvement is due to further cool down or gradually better seeing conditions. When there are thermal problems they do disturb the intra and extra focal rings on star images but they are still concentric rings either side of focus, unlike the ones you've shown. I recall that fans can introduce vibration which could cause the diffraction pattern to deform, might be woth trying without.
  14. @Midatlantic. Most reflecting telescopes these days are designed to be photo compatible, this requires that the camera can be focused nearer to the telescope than an eyepiece. To allow the eyepiece to be focused instead, an extension piece is usually supplied to position the eyepiece further out. The "problem" is when the new owner is unaware with this.