Originally posted by BigBangPhotography
Hi all,
I'm currently using the 77mm on my K3-ii and absolutely love it! I'm considering upgrading to the K-1 and I have been wondering if the actual focal length would change due to the FF sensor compared to the APSC sensor? If so would the lens work as a wider lens on the K1? and if so what would the resulting focal length be? I currently use the lens for half body portraits and I'd like to gauge an idea of how much wider this lens would feel, i.e if I stood at the same spot, would this lens still be a half body portrait lens or would it become say 3/4th body portraits?
A 77mm lens has a focal length of 77mm whether it's mounted to a Q, an APS-C, or FF camera. The only thing that changes focal length would be a teleconverter. The angle of view would be wider on the K-1 compared to the K-3 ii.
A lens projects an image circle onto the sensor. Depending on the sensor size, the image has a wider or narrower field of view. The image from Google below shows an example of this in Nikon's FX (FF) and DX (APS-C) sensor sizes. The subject is the same size in both because focal length doesn't change.
You may read about a DA lens vignetting on the K-1. That's because the image circle projected onto the sensor isn't big enough, so corners are black. This is typically why FF lenses are slightly larger and heavier than APS-C lenses. Here's another example from Google: