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Old 06-10-2011, 09:27 PM
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mental4astro (Alexander)

mental4astro is offline
Join Date: Jun 2008
Location: sydney, australia
Posts: 4,862
OTA modification that may help at the eyepiece

Tips and techniques that can help I see as a big part of this thread. I posted this originally in the DIY section where I had started a thread on the DIY dob mount that this 8" f/4 OTA.

As I use this scope a lot from home, the ambient light is a real pain in the neck reflecting off the white tube. I had some foam rubber left over from the stuff I used to wrap around the poles of my 17.5", so I used it to cover the top half of the 8" OTA. I cut out the necessary openings to accomodate the focuser, finder shoe and spider nuts. The white markings were done to position these openings.

The foam rubber sheet is wrapped around the OTA and only glued onto itself, not the tube. The holes that the various components poke out from hold the thing in place so it doesn't slip. I made it a snug fit which helps too.

The result works really well to tone down the reflections, . An added bonus was the insulative effect it had on the secondary mirror, protecting it from dewing up for a longer time than before. A bit of a surprise that was. I might consider making a dew shield for it out of thicker foam, much like the ones used on SCTs. Even at a dark site, this simple mod has improved the reflection attenuation off the OTA.

This stuff weighs bugger all, so it doesn't upset the balance.

Below are a couple of pics showing before and after.

Another thing I've done was paint the focuser board of my 17.5" matt black, specifically using black coloured blackboard paint. This was considered from the planning stages of the scope, and I've never had the same problem of reflections coming off the board.

Some food for thought.
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