this is not an expert test or presentation, the photos are from hand and taken by accident when writing this text, there is a small frame shift because the camera is not static on a tripod, thanks for understanding,
settings on K1 (FF photo body) with F50 / 1.7 (FF lens) for both FF and APSC format are the same:
aperture: f1,7
shutter: 1/80
ISO: 100
lens: Pentax F 50/1,7
camera: Pentax K1
here I just tried on K1 + F50 / 1.7,
in the 1st case it is in FF mode
in the 2nd case it is in APSC (cropped) mode,
in the 3rd case it is in FF but truncated in PS to APSC mode
1.
2..
3.
at first it seems that the differences with the same lens on the APSC and the cropped FF mode do not exist, they do exist-in the last two photos pay attention to the background, you can see the difference in perspective, to get the same photo in the last image in APSC mode I had to move approx. 2 meters backwards so that the whole car would be in the frame as in FF mode
,at greater distances than this example of mine this difference in perspective is very noticeable, a direct difference with the same FF lenses on an FF camera or APSC camera with the same settings and the same focus point / same distance from the frame is obvious
one example FF with settings:
aperture: f4,5
shutter: 1/80
ISO: 100
lens: Pentax FA 80-320/4,5-5,6
in 35mm: 110mm
camera: Pentax K1
one example of APSC with settings:
aperture: f4,5
shutter: 1/80
ISO: 100
lens: Pentax FA 80-320/4,5-5,6
in 35mm: 110mm
camera: Pentax K1
a little more theory:
pictorial representation of the size of the sensors and their displays
an obvious difference in perspective on different formats with the same lens with respect to the crop factor and the same settings
I switched from APSC format to FF primarily because I really like the perspective provided by FF, ie I prefer DOF (depth of field) provided by FF system than APSC system (FF also has better iso / better dynamic range), but that is just my personal commitment in the desires I want to have with my photo equipment, those who always want high depth of field / large part of the frame or always the whole frame in focus and a very large focusing range with smaller size and overall lower weight will choose the APSC format
or some other smaller eg MFT m4 / 3 format