I think that rob's point is that while focal length is nearly the same, AOV isn't, and hence a comparison of AOV is more pertinant to the discussion of APS vs FF. Comparing the DA 14mm with the FA 20mm shows nicely how the APS lens isn't a saving in size and weight (or cost!) for an equivalent AOV. You talk about an APS camera. The *ist D is not one of these - it's a 35mm body with an APS sized sensor in it. An APS camera would have a smaller lens-film distance, a smaller mount or something like that. The *ist D is saddled with 35mm's heritage.
Cheers, Procrastinating David
