Hey, welcome!
Originally posted by dili Using aps-c lenses on full frame will reduce the amount of megapixel, but in how far will dynamic range be affected as well?
I am not sure what you are talking about.
Total megapixels of the sensor will not be changed. But there is a chance that APSC lens will not cover the edges of the sensor. So you might have to crop the frame to APSC (or slightly bigger). But this doesn't mean the lens loses MP, its resolution does not change. Most lenses will still outresolve the FF camera or an APSC camera. And many DA lenses actually cover the FF normally, so you don't lose anything:
https://www.pentaxforums.com/forums/54-pentax-lens-articles/31629-da-lenses-f...ts-thread.html
Actually rather few K-mount lenses are truly only for APSC.
Originally posted by dili but in how far will dynamic range be affected as well?
Not at all. Why would this be affected? The lens will project the same colours and contrasts and brightness regardless of the camera it is mounted on. What happens after that depends completely on the camera. Generally speaking, newer cameras have better DR than older ones.. And higher end, more expensive cameras, have better DR than cheaper ones. So we can expect the Pentax FF to be quite good in that department, probably better than the K-5IIs.
But as stated, the total recorded DR depends on the sensor and camera technology. The lens itself of course has an effect on the image, but it is independent of the camera and will not change if you put it on a different sensor.
Just keep in mind the lens and sensor are two independent things. They only come together because the output of the lens is the input of the camera. And if the camera's sensor is bigger than the lens' projected image circle, the edges of the frame will be dark or low quality. But that is rarely a problem.