Originally posted by storytelling Hello Everybody!
I'm wondering if some one can tell me if the :Pentax 35mm F2 PFA SMC AL on my K3 will look almost the same as my 50mm 1.4? (since is a Full Frame lens)
The focal length is a physical feature of the lens and is independent of whether the lens will be mounted on a film/FF or APS-C camera. You don't need to convert anything--a lens that is 50mm that was made 40 years ago will give the same field of view as a 50mm lens that was made yesterday. It's a bit confusing because people talk about "equivalent focal length" and whatnot. Ignore all of it. It's meant for people who are used to film cameras and want a comparison they will understand.
The "FF compatible" lens part involves the back of the lens, the "image circle." A FF compatible lens has a circle that is wide enough to contain the 35mm sensors, while an APS-C only lens has a image circle only wide enough for the smaller APS-C sensor. In Pentax lingo, APS-C lenses are denoted DA while FA/FA* are used for FF compatible lenses. This is a bit of a misnomer, as some DA lenses are FF compatible, but it's model by model. Anything designated FA, however, is.
This image shows a manual film lens (left) with a Sigma lens compatible only with APS-C cameras (right). The image circles are highlighted in red. Notice how much smaller the Sigma's is?
IMG_1009.jpg
Last edited by MadMathMind; 10-09-2014 at 09:44 PM.