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Old 20-05-2018, 11:44 AM
glend (Glen)
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glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 5,412
Quote:
Originally Posted by DaveNZ View Post
Good points Glen. Yes, I'm probably expecting too much from the price point.

Not sure off the top of my head of the combined weight of the Litecrawler and QSI683. I have solved the "weight issue" with the carbon fibre rods which was low cost. (rods from Ebay)

The real issue is the secondary. You would have the same issue I'm guessing with the original GSO focuser and a light weight camera. I was getting movement with my collimation laser with no camera attached and my lighter Moonlite focuser.

Cheers Dave
Both the GSO dobs I have owned, a 12" and a 16", suffered from secondary sag at various altitudes, easily observed with a laser collimator in place. The 12" was a solid tube model and the 16" was the strut model. I managed to control it in the 16" by using "string bracing" of the top section, as used in Dennis Steele's string dobs ( on the Dob Stuff website).

The 'string' I used was actually non-stretch Dynema synthetic boat running rigging, 2mm; attached to small turnbuckles secured to the top and bottom section rings in triangulated arrangement. It only took three of this strings to correct the top section movement.
I figured using steel guitar strings on the big Dob would introduce expansion/contraction with temperature fluctuations. I know my guitar goes out of tune with temperature changes.
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