Sky 90 II dew shield dimension ?

Started by Martin Willes, 12/03/2008 03:23AM
Posted 12/03/2008 03:23AM Opening Post
Could somebody please tell me what the outer dimension of the new f/5.6 Sky 90II dew shield is. Is the dew shield easy to remove and if so what is the outside dimension of the OTA? Thank you in advance for any help. Martin

"In the beginner's mind there are many possibilities, but in the expert's there are few." Shunryu Suzuki[COLOR="Blue"][/COLOR]
Posted 12/08/2008 03:43PM #1
The OD is 114mm. The thread is very fine so great care should be taken when removing the lens shade. Hold the lens ring as tightly as possible and then unscrew the lens shade. When it will be reattached, it is important to proceed with great care to prevent cross threading.

Art Ciampi
Posted 02/19/2009 06:07PM #2
A bit late but I'll add a few more notes to this. The dewshield is threaded on BOTH ends with the identical threading. It is fairly easy to remove from the OTA. On the objective end a stop ring is threaded in so that the dewshield cannot retract further than the front of the OTA. If you are considering getting an adapter for a Coronado or Lunt solar filter, there are several companies making adapters which thread in directly to this thread. Normally this works out wonderfully and the solar filter cannot slip off accidentally. In my case I purchased an adapter which was not for the Sky90 but it looked ok. When I threaded it in, it seized short of going on fully. I had a heck of a time removing it and managed to partially destroy those front threads doing so. It was NOT cross threaded, just incorrectly threaded, probably with a non-metric thread. When I finally did manage to get the proper adapter it, would not thread in reliably enough. I had severe concerns with the rigidity. One really doesn't want the filter falling off when observing the sun through a telescope. I ordered a replacement Sky90 dewshield from TNR but it is only threaded on one end and has no provision for installing the stop ring. It is an obsolete part probably for the original series of Sky90 telescopes. Once I saw this I inspected the original dewshield closer. I managed to remove the stop ring, measured the threads which turned out to be identical on both ends and reversed the dewshield on the telescope. The threading on the sliding ring on the OTA is longer and goes past the mangled portion of the dewshield threads and is rigidly held. The solar filter adapter threads in properly to what used to be the OTA threads and is also rigidly held. I even threaded in the stop ring. I am happy in that I can now use the Coronado 90 filter I purchased. I am not happy I wasted my money on a replacement dewshield that is not current and cannot be used.