I'm looking to extend the range of lenses in my Mamiya RB system, the longest I currently have is the 140mm Macro which is great but not quite long enough to isolate flowers against an uncluttered background. In 35mm I would usually use a 200mm macro for this, so am looking at the 250mm (about 120 mm equivalent focal length/angle of view) or the 350mm (equivalent to 170mm on 35mm). At the moment I'm erring towards the 250mm. The new KL version of the 250mm comes in two flavours, APO and non-APO, one being twice the price of the other. Is it worth it, does the APO really make that much difference? Of course there are quite a few Sekor C 250mm's floating around as well, I don't know how these perform compared to the KL versions. Any advice would be most welcome!