APM 152-1200ED APO Doublet

In February 2014 I installed a new telescope into my relocated observatory – an APM 152-1200ED APO 6-inch refractor.  The photograph shows the telescope mounted on a Skywatcher AZ EQ6-GT mount in the observatory. 

The 152-1200ED features an air spaced doublet lens cell using ED glass equivalent to FPL-51 complimented by a Lanthanum coated element for good colour correction at a focal length of F/7.9.  The scope is fitted with pre-production lens cell No. 003 which was measured to have a 0.967 Strehl ratio at 587 nm (green).  Zero degree interferograms of the lens cell at different wavelengths taken from the test report are shown in the right inset.

My telescope is a customised version of the basic model with a Krupax tube and 3-inch APM rack and pinion focuser.  Krupax enables a strong but lightweight tube construction with excellent anti-dewing properties and an optimised knife edge baffle design which extends into the extra long dew shield.

The left inset shows the imaging train which includes the dedicated Massimo Riccardi designed APM x0.75 Reducer. This reduces the focal length to 900mm to give an imaging focal ratio of F/5.9.  The other components of the imaging train are: SBIG ST10XME CCD, Atik EFW2 filterwheel (9 x 1.25” filters), Teleskop Service TS-OAG9-M48 off axis guider and Starlight Xpress Lodestar autoguider.