Novice question here, how do you mean stop down?
I did try using larger f/'s but werent getting the images i wanted, had loads of nasty glare/sun reflections of the cars body work, and too much DOF for my liking. The day for me was a more of an experiment day, the best pics i got where with the polarising filter fitted. i got loads like the last one i posted.
The last is also the only edited on a my screen, i found my old one's w/b was well off..
The hardest part of the day was the lack of running