Carey Mask for larger aperture   3mm perspex gave poor results with the 6" reflector. The 10" has recently been refurbished and a Carey Mask from 3mm black perspex was made. Initial tests with a hazy sky and bright moonlight are encouraging. The star is Altair which is conveniently placed for focussing during Summer and Autumn. Exposures 15 seconds. Left hand image: Out of focus clearly seen. Large gap between left hand spikes. Requires anti-clockwise rotation of focuser.   Right hand image: Much closer to true focus. Spikes below the star are a little brighter and easier to see. Also Altair. A much shorter exposure of 1 second. Out of focus seen by split in left hand green section.     The importance of good tracking: Periodic error in the tracking not only ruins images but interferes with focussing. This picture shows that a shift caused by tracking error destroys the focussing image. Fortunately there are places in the mount's cycle when error is much less, making focussing feasible.