The focal length of a lens never changes..so a lens never turns into an different focal length lens. the sensor size changes.
so take the lens, multiply the focal length by 2.3 (for BMCC, 3 for BMPC)and that will give you the approximate FoV comparison.
For example, your 10mm lens on the BMCC has the FoV of a 23mm lens on a 35mm sensor. and your 50mm lens has a FoV of 115mm lens on a 35mm sensor.
By the way i have the Rokinon 16mm lens M43 mount n the BMCC and it is a very sweet lens. extreme close focus, great edge to edge sharpness, on the cropped BMCC sensor anyway.
I’m interested to mount some 16mm cine lens on it and try those.
I would like to see how an Angenieux 12 – 120 Arri bayonet mount lens would look on the BMCC or the BMPC. So i think i’ll buy one on eBay to test it out.
I have an order in for the BMPC but wont receive until Dec.