In my insanity, I have bought a 18' x 30' canopy to use as a portable studio. Yes, I'm nuts. However, the canopy has a white tarp top. To shoot bikes with, I'm going to make a large difusion panel. 5' x 18' and hang it like a ceiling in the canopy at one end. I'm going to place two WL x3200's above the panel. The bike will be place about 3 ft from the end of the canopy on the inside, directly below the panel. I'm going to overpower the daylight and use a ND filter. I'm putting the bike so close to the end of the canopy to catch the ambient light coming off the bike. I'll be shooting into the canopy. Inside the canopy, I have a white backdrop cloth that spans the width of the canopy (18'). (I could get an extra 2 more feet at each end. the cloth is 22' long.)
Now, having said all this, my question follows.
How far back from the subject (the bike) should I put the backdrop? I'm not looking to have the backdrop show up has white, but somewhere between a light and medium gray. Maybe a gradient kind of effect.
The reason I ask this is because it would be easy to hang the rod for the backdrop on the canopy legs, which would put it about 6 - 7 feet away from the bike. If I don't attach it to the legs, then i need to build a couple of support legs for the backdrop rod, and then I could put the backdrop rod at any distance I needed, til I reached the other end of the canopy.
Any suggestions would be appreciated.