Originally posted by oh_9000 I also understand that if I take for instance DFA 100mm macro lens and mount it on my K3, the pictures it takes would be same as with using a 150mm apsc designated lens.
Actually, you don't understand. A DFA 100mm, an FA 100mm, and a DA 100mm would all have the same field of view on your K3. The letters in front don't change the focal length.
If you mount all of them on a K1, they would all give a wider field of view than what you see on your K3. But, the DA lens would be dark in the corners because it is designed to project a small image circle. Some DA lenses actually work on a K1 because their image circle is large enough, even though they were originally designed for the small APSC sensor.
Note that there isn't really a DA 100mm. I was just using your example. A better lens would be the 50mm's. The DA 50, DFA 50, FA 50, Tak 50, etc would all have the same view on your K3. Mount them on a K1 and they all give a wider view. The DA 50 would have dark corners on the K1, but its visible area would look exactly the same as the other 50's.
---------- Post added 04-17-19 at 10:32 PM ----------
If you like the Tak 200mm lens on your K3 but you want a more modern lens that will give you the same look, then get the DA* 200mm, or one of the FA* 200mm lenses. They will all give the same field of view as the Tak.