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New Super Dew Shield

Started by fugardi, 10/14/2006 05:52AM
Posted 10/14/2006 05:52AM Opening Post
In my continuous effort to solve my local heat wave turbulence problem, I modified my existing 16" dew shield with a Walmart sleeping bag pad. By attaching it with with velcro, trying to keep the open side slightly larger, it is now 24" and extends outside my dome opening by approx 10". According to the internet sites, it is recommended to have a dew shield 1.5 to 2.5x the scope aperture. For my C11, this super dew shield boosted the ratio from 1.5 to 2.2x. With average seeing last night, I was absolutely amazed at the sharpness of Uranus 1hr after its peak altitude with the reduced turbulence. Please see my star test on next posting

Regards,
Steve

Attached Image:

fugardi's attachment for post 33940
Posted 10/14/2006 06:04AM | Edited 10/14/2006 06:05AM #1
After viewing M45 I couldn't resist trying an f25 star test on one of the 7 sisters. I took 2 30sec avi's, one with my box fan (located in the doorway) on high and the other off. Previously, having the fan on was better than off, however I never optimized the speed (low, med, high). With the super dew shield, my star test shows that no fan is actually better than the high speed. I should have tried each setting but didn't think of it last night. I have never been able to capture any decent diffraction rings on a real star with my webcam until last night. My theory is that while the fan can overcome some thermal turbulence, too much causes unsteady air. Finding that ideal condition is the key to optimal viewing in my dome.

Attached images are the best 60 of 300 frames, resized 8x (left is fan on, right off). Maybe this simple dew shield modification can help you?

Regards,
Steve

Attached Image:

fugardi's attachment for post 108152