TMR Design wrote in post #8547499
Rich,
You're still missing the point. I haven't assumed anything. If the person is shooting at 1/20 or 1/200s the exposure is going to be the same. I'm commenting on this one point you've made because it's incorrect. The other methods are fine to point out but to tell someone to increase shutter speed when there is no ambient contribution is not sound advice. As I said in my original post, in the studio environment, shutter speed will not be one of the ways to control the background exposure.
I'm not sure why you want to keep arguing that point. The other methods work but the photographer has to be very careful and perhaps use the inverse square law to know for sure that he/she has actually rendered black. I can shoot tons of images that appear to have black backgrounds based on the image on the camera's LCD and I (or a client) would be very disappointed once I viewed them on the computer if I didn't at least have something scientific or defined to know that I achieved black.
Robert- I gave some thought to why I'm arguing the point and the best explanation that I can come up with is that I don't agree with you
First, I don't believe that the OP has a light meter so while I agree with you that it would be the ideal way to go, it isn't always an option. He's shooting with two Canon flashes.
In your studio you may not be getting much ambient contribution but that is not to say that in another studio with more, larger, and different facing windows than you have that someone else won't be getting much more ambient light. Hey, I'll call you tomorrow and we can argue this out over the phone 
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