I have both the CED1 and CED2 and am testing them out. Though Bill has not given me any details, I believe these diagonals are special purpose with special benefits depending on what you're observing in concert with the aperture of a scope.

That said I know that they act as interference filters. In diagonal form, they are purported to be a 1/10 wave after coatings. Additionally, their 45 degree angle negates any reflections that occurs when using the screw on the eyepiece type of interference filter. The CEDs really reduce eyepiece scatter when viewing the Moon.

I can also compare these diagonals to one-off infereference filters I have with known, at least to me

, peaks of transmission. I have been using interference filters for years and have approximately 25 of them. Most of them for beta testing.

To compare these to run of the mill filters or polarizers is somewhat of a mistake.

The best thing out of the box about these diagonals are how well collimated they are simply inserted into my refractor. Both diagonals I received are spot on. I can't say that about any other diagonal I have ever owned.

More later.

Best,