Shiraz
03-04-2013, 03:32 PM
have had a continuing battle to get consistent results from an f4 GSO Newt. Latest change seems to have yielded significant improvement.
the problem was that moving the scope around yielded obvious movement in a laser collimation spot projected onto the primary. it seemed to have many different stable positions and could move from one to another - with maybe as much as 1cm change in spot position - without warning or apparent reason. Also similar behaviour (bit less dramatic though) with a moolite focuser. Eventually tracked it down to the way that the focuser clamp works - it is based on keeping two cylinders aligned but the clamp only acts at one end. when I put a Barlow tube in the focuser it was easy to move it around by pushing on it from the OTA side. When you think about it, the slot for the brass compression clamp limits the locking surface to the very thin outermost lip of the draw tube - asking for trouble.
solved the problem completely by fitting an additional screw to clamp coma correctors/ Barlows in two places along the focuser as in the image. The screw on the compression ring holds the weight and the inner one is tightened just enough to stop any movement between the two tubes. Works a treat and now the laser spot stays fixed regardless - I even removed the primary, washed it and replaced it to find that the whole system required only a minor tweak on the primary - previously unheard of.
this mod appears to turn the GSO focuser into something usable for imaging with camera weights up to maybe 800g, which will be quite suitable for an OSC on this scope. Will be able to try it out with my QHY8 when the clouds clear. Also want to try the mod on the Moonlite next - very simple mod since there is free space for the screws.
the problem was that moving the scope around yielded obvious movement in a laser collimation spot projected onto the primary. it seemed to have many different stable positions and could move from one to another - with maybe as much as 1cm change in spot position - without warning or apparent reason. Also similar behaviour (bit less dramatic though) with a moolite focuser. Eventually tracked it down to the way that the focuser clamp works - it is based on keeping two cylinders aligned but the clamp only acts at one end. when I put a Barlow tube in the focuser it was easy to move it around by pushing on it from the OTA side. When you think about it, the slot for the brass compression clamp limits the locking surface to the very thin outermost lip of the draw tube - asking for trouble.
solved the problem completely by fitting an additional screw to clamp coma correctors/ Barlows in two places along the focuser as in the image. The screw on the compression ring holds the weight and the inner one is tightened just enough to stop any movement between the two tubes. Works a treat and now the laser spot stays fixed regardless - I even removed the primary, washed it and replaced it to find that the whole system required only a minor tweak on the primary - previously unheard of.
this mod appears to turn the GSO focuser into something usable for imaging with camera weights up to maybe 800g, which will be quite suitable for an OSC on this scope. Will be able to try it out with my QHY8 when the clouds clear. Also want to try the mod on the Moonlite next - very simple mod since there is free space for the screws.