|
Hmmm, a couple years ago now I had a Coronado diagonal that showed oxidation of the energy rejection filter. This is the filter in the diagonal thats in the focuser end of the diagonal. Its actually two discs of glass with the erf coating between the two discs. This glass sandwich is supposed to be sealed at the edge to prevent oxidation of the coating by contact with the atmosphere. Over the period of a year the coating degraded from the outside edge gradually creeping in towards the centre. Solar detail became increasingly difficult to discern. See the attached image showing the mottled appearance of the degraded coating and the remnant of unaffected coating at the centre of the filter.
|