Recoating the secondary mirror

The secondary mirror of my Obsession telescope really needed a new coating.  When looking at it, I could see the back of the mirror through the coating.  I sent the mirror on August 11 to MCM Optique in France to be recoated.  However, my secondary mirror had a strange di-electrical original coating (with probably 40 - 50 layers of ZrO2 - SiO2).  This made it impossible to remove the original coating from the mirror.  

Alain from MCM Optique measured the reflectivity of the mirror at different wavelengths, which made it clear that certainly at the blue parts of the spectrum, the reflectivity had become very low.  Also in the green (around 500nm) and in the red, the secondary mirror was below what is needed to observe.  

The reflectivity of the secondary mirror

Alain proposed to cover the existing mirror with a new layer of aluminum, without removing the old coating.  This is not the best solution, but the quality of the newly coated mirror seemed to be very good.  

The mirror was sent back on September 22, arrived on September 26 and was reinstalled on September 29.  Let's hope for some nice weather now so I can test the new coating!