Changing the focal lenght will only affect the size of your car. You should keep the film gate and change focal lenght to 70mm for example (if it gives you the size you want and or if you matched your camera to 50mm) if you don't wanna move the camera and if you don't want to scale the car itself.
Maybe it became a liiitle too big in my example but should be something like this
Fine tuning up to you ^^
Cheers,
exidge
Maybe it became a liiitle too big in my example but should be something like this
Fine tuning up to you ^^Cheers,
exidge
