Originally posted by shiestmiester parallax - i agree 17mm is 17mm. however when you are using a full frame lens on an APS-C size sensor you get the 1.5x zoom factor. This makes a FF 17mm a 23.5mm on a pentax DSLR.
Great for telephoto (300mm=450mm) not so great for super-wide, hence why i purchased the Di II lens for wide application.
Did no one else know about this?
~T
Yes, and when you use a 17mm APS-C specific lens on an APS-C sensor you get EXACTLY the same effect. 1.5X factor! (Vs FF) 17mm FF and 17mm APS-C capture exactly the same image on an APS-C sensor. This is easy enough to demonstrate. Put your camera on a tripod, put your SMC M 50mm 1.7 on and take a picture. Now put your 17-50 on, set it at 50mm and take another shot.
EDIT: Don't you find it a bit odd, that with the wealth of knowledge and expertise on this board that "no one else knows about" it?