Originally posted by Pål Jensen Maybe because it isn't?
I suspect real SMC is too expensive. I've notice a decline in flare supression from Pentax since the 70's....
To be fair, in general the trend since the seventies has been to lenses with more elements (and indeed zooms), which can itself impact flare suppression. However, your notion that Pentax has (at least at times) cheapened out on SMC coatings of their lenses is demonstrably true. Lentip.com/optyczne.pl, when they tested some Pentax lenses, did test transmission
The results (in percent lost per surface):
DA 17-70mm 0.3%
FA 43mm Ltd 0.4%
DA 35mm f2.4 0.4%
DA 100mm WR Macro 0.5%
FA 50mm f1.4 0.6%
It is a secret (although perhaps an obvious one to some) that coating quality decisions at Pentax are made on a per-lens basis. While they may have several general levels (SMC, HD, Aerobright), just calling it SMC is no guarantee of the newest, best SMC coatings (even in the seventies, after all, Pentax claimed that SMC resulted in a loss of only 0.2%), and one should expect cheeper lenses to have lesser coatings.