Originally posted by Luddite I understand the crop factor element on DSLRs, I use legacy film era lenses. Question is if I purchase a modern 50mm fixed does the crop factor apply or do I get a true 50?
There have been many threads on this topic, so feel free to search for them.
That said, all 50mm lenses are 50mm, that is their lens property, and they project a certain angle of view, and a certain image circle diameter. How much of this image circle is captured depends on the size of the sensor, though. This is why the same 50mm lens on 645Z is wide angle, 50mm on FF in normal, 50mm on APSC is slightly tele, and 50mm on Q is telephoto. Because you see a smaller cutout (and this cutout has higher resolution, typically, since smaller sensors have higher pixel density). However, for a lens to make a big image circle, the lens itself has to be big, as well. This is why a lens made for FF is typically designed to project an image circle big enough for the FF film/sensor, but not big enough for 645 format. This is why you cannot use a Q lens on your APSC camera - the edges would be black, with just a small circle in the middle of the frame.
So, now you know. Focal length is a lens property, independent on camera. Angle of view, however, depends on both focal length and film/sensor size. You can use lenses from bigger formats on smaller formats, if you don't mind lugging around a huge lens. You usually get heavy vignetting if you use lenses from smaller formats. That said, many DA lenses are FF compatible - there is a thread with test photos, just search for
DA lenses on full frame. Oh, and having a huge image circle is not necessarily great, either. It means more glass, which projects light onto nothing, so its useless, and the extra light can bounce around the mirror box and cause odd flares, loss of contrast,.. basically, the best is to have a lens with image circle just right for the camera's sensor.
If you buy older or bigger lenses, they will give the same field of view on your camera, as DA or APSC crop sensor lenses, if they have the same focal length