Solar filters 

I'm a newby to surveying so please forgive the ignorance if it shows.

I recently bought a new Pentax CST-225N to use in archaeoastronomic research. I will need a solar filter for this total station, but I'm having a hard time finding one. My understanding is that the EDM electronics can be damaged by pointing the instrument at the sun. Therefore, the filter needs to be an objective filter, not an eyepiece filter. If I can't get a filter from either Pentax, or Berger (they actually manufactured the instrument), then I've wondered if a solar filter such as astronomers use for their telescopes could be used on the total station. These filters come in many sizes, and different types, i.e. hydrogen alpha, calcium K and others. Does anyone have any previous experience with non-manufacturer provided solar filters? Any help would be appreciated.

Thanks.