Sunday, July 18, 2010

Focuser tube baffling

I've been having bad light control problems with my 13mm Hyperion eyepiece in my 13".  Whenever there is anything even slightly bright opposite the focuser--even if it's just skyglow at a pretty dark site--it was flooding the field of view.  So I made a simple focuser baffle.  I just cut a cardboard ring with inner diameter just over 1.5" and outer diameter 2.2".  The inner diameter was arrived at by ray-tracing.  The outer diameter fits the focuser tube.  I then just slip it into the inner edge of the focuser tube.  Because the focuser tube inside is threaded (or just ringed) it stays in.  I also added a wide ring around the outside of the focuser tube, inside the scope's OTA, but I don't think this was what made the difference.

Result: Great!  Last night, I was able to observe with the 13mm despite the moon, a family fishing with a light hanging over their stuff, and boats in the water.

I also have a large foam light-shield, which I occasionally used, but the baffle ring seems to render it unnecessary.

I expected the baffle to vignette the field of view of my 30mm Super-View, but I left it in for convenience even when I was using that eyepiece, and the views were fine.

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