Originally posted by egordon99 Ah, but you can see from that why I was confused.
In this case, it was a digital lens, and the advertising for it says "The super wide-angle capability of this zoom lens (equivalent range of approx. 15-30mm when used with a Pentax digital SLR camera" makes it sound like if you put this lens (which has different mounts for different brands) on any camera it will be a 10-20 mm, however if you put it on a Pentax it will be the same as a 15-30mm lens!
Their wording is inaccurate. Thus, the confusion.
This is not the same question. That is a lens made for digital cameras going on digital cameras, and my question was why was it different if used with the Pentax. This is a question about 35 mm film lenses going on digital cameras, which I had (mis)understood to have some advantage.