Hi I have an exposure problem that I think I have figured out but would like to run past everyone.

I am using 5x4 and I need to photograph at F/16. With my bellows extension and Infrared filter I need to factor in 10 extra stops in total. My subject is delicate and prone to imperceptible movements of which I cannot control so I need to try and capture the image as fast as possible to eliminate movement.

My flash heads will fire at F/128 giving me 6 extra stops (from F/16) in one flash. If I flash once, then reduce the power on the flash heads to F/64 giving me 4 extra stops (from F/16) and flash again will this give me the 10 extra stops I need in 2 flash pops?

thank you for your advice

Jon