I have learned that Custom Scientific has recently (one year?) changed the design of their photometric filters. Instead of using the classic colored glass sandwich to match the Johnson Cousins system with Bessell prescription they now use a single piece of fused silica with an interference coating on one side and an anti-reflection coating on the other side. As a result the shape of the transmission bands is different compared to the old filters. I attach a pdf showing the comparison.
I just wonder whether the new design is still good to do the photometry as I guess the transformation to the standard system is likely to be quite different. I also think the observation of novae in ouburst might be troublesome as, for instance, the Hbeta line might be shifted bluewords and be off the passband of the V filter.
Thank you for your comments.
Gianluca
I wonder....if observers are at a point when they want to buy *new *filters and are considering those filters mentioned above which have a more "square" transmission curve compared to the standard UBVRI filters we know and love.. should they perhaps instead make the transition to Sloan filters? I don't mean this as a rhetorical question at all, there are real downsides IMHO to Sloan filters like giving up on data continuity with centuries of legacy observations (Johnson V is intended to mimick human perception and B was kind of similar to certain photographic plates I understand), and comp stars are in UBVRI mostly...still the pros seem to move to the Sloan system.
(since none of those filters seem to be currently avilable anyway now it's kind of a moot discussion, but hopefully there will come a day when we can buy filters again...)
HB