I'm in the market for a B60 yellow or orange filter and have been amazed by their prices, compared to similar B50 filters. I was wondering why this difference? Is it because color film dominated during the B60 production years, thus b&w filters have become "rare"? Is it because the number of old B50 lenses have fallen off and nobody wants that size of filter these days? Or something else? For example, I can find perfectly good B50 yellow or orange filters for as low as $15; B60s are in the $75-$150 range, and more often at the high end.