White backdrop lighting advice

absplastic wrote in post #17772383
It depends on what ends up being the most limiting factor. With low-powered lights like speedlites, there is no guarantee you can overexpose a large enough area of a grey wall while still staying at the shutter speed, aperture and ISO you want to use. If you are happy cranking up the ISO, what you say is true, but I'm assuming for portraits that keeping ISO low is a consideration.

Also, if your setup looks like Malveaux's test shots, where the subject is actually sitting on the floor of the infinity sweep, grey isn't going to be able to be used as white.

For subject on gray bg, agree would be really hard to make it white. But for bg, personally a hot shoe is plenty IMHO. You have aperture to play with also. Not everything needs to be f8 for portraits.

Here is simple example. Just regular wall as bg. One light at very very low power. Not exactly the case we discussing here but a lot can be done easily with speedlite (even though I don't use them). Main issue with speedlites is making them fill the modifier but with in-direct ones it is quite easy. And adding that flash head deflector helps even though it eats more power.

The other thing to note about speedlites, is that the umbrellas in the diagram I posted might not be necessary in a small space. I haven't tried it, but it might just work to set the zoom heads of the speedlites to a wide angle and aim them bare at the wall. They should be directional enough to not spill onto the subject, the only question is whether or not the spot they project is uniform enough, or if the brightness falls off too quickly from the center. Worth a test shot before troubling with the umbrellas anyways....

Here is an example done with the setup I described (albeit not with speedlites). This photo has two 1000 W/s heads on a Norman 40/40 lighting up the backdrop via 43" black/silver reflective umbrellas, and an Adorama Flashpoint 620M lighting her from the front and camera left using a plain 24" x 36" softbox. There is a bit of post-crop vignetting on this as was necessary for the context where this photo was being used, the slight dimming in the corners is not due to the lighting.

Generating a white b/g is easy enough with a white wall and white BD. A complete portrait can even be shot with a single light if you accept limited placement options for the key. I remember why I hate SOOC white backgrounds after doing this exercise. Exposure was set to drive virtually the entire b/g to FFFFFF: white BD, 150Ws, ISO 100, f/8. Subject was flagged except for the front of the face, where light was diffused by a panel and stray light scrimmed. Backlighting nonetheless acts as a light source.

Result after processing, but no special b/g treatment: