Removing the dew shield and lens cell on a Chinese carbon fiber(and aluminum) refractor

By: Vlad Fedosov
03/22/2018

Intro:

Having recently acquired an excellent Astro-Tech 80LE 80mm ED refractor I noticed a few small issues with it. The dew shield was quite loose and had a lot of play in it. Also, the internal felt lining was starting to lift off from the OTA by the lens cell. While these small issues did not prevent the scope from operating properly I’m the type of person that cannot live with such imperfections in an otherwise perfect instrument.


DIY Guide:

I knew that the dew shield and lens cell would need to be removed to complete the repair of my little APO. Unfortunately, I came up short on finding a how-to guide to remove the dew shield on a carbon fiber version of these scopes. The aluminum version apparently has a thread where the rear ring can be unscrewed from the dew shield. After trying to do this as hard as I could my dew shields rear ring would not budge. Then I got to thinking that there is no way that they could have put a thread into the carbon fiber material. When I tried pulling the outer ring off I did noticed that there was some movement in it. After pushing it outwards with my fingers I was able to get it off. It is simply glued onto the dew shield. In retrospect, I think applying some heat to it would make the glue a bit easier to break loose.


The next step is to slide the dew shield back to expose the screws that hold the lens cell in place. From what I can tell these look like collimation screws but on my scope they do not seem to affect the collimation. Back out the (3) inner screws and remove the lens cell(note its original orientation). Next, if you need to remove the dew shield completely you will need to remove the 3 screws that are holding the lens cell mounting ring. At this point, you can slide the dew shield off the OTA.



If you are attempting to fix some dew shield looseness as I was all you need to do it ad a bit of thin felt/flocking paper to the ring where it contacts the body of the OTA. You need to experiment with how much you need to add to get it to feel the way you like, but it is much less material then you would figure. Assembly is the reverse of taking it apart. Once I reassembled my scope it had perfect collimation without any adjustment needed. When you are reattaching the outer dew shield ring use some kind of nonpermanent glue.