August 26th, 2010
I’m amazed by the number of people I talk to that are mixing flash with the bracketing shots they are shooting for Exposure Fusion (Blending in Photomatix) and HDR. Plus I’ve gotten a number of questions asking how to to shoot brackets with flash.
The first question is why? What’s the point of using flash when you are shooting brackets? You thought the reason you shot bracketed exposures was so you didn’t have to use flash, right. Well the fact is that when you use HDR or EF for interiors you tend to get low contrast results (more so with HDR than EF). That is, the blacks are not as black as you’d like and the whites are not as bright and crisp as you’d like. The term that comes to mind is muddy colors and dirty whites. You also have issues with white balance. It turns out that if you add a kiss of fill light from a single flash makes these problems much better. If you add a little fill flash to your brackets you don’t have to spend as much time and effort in postprocessing to get rid of the muddy colors and dirty whites.
Also, adding a touch of fill flash to bracketed shots can be done without having to “climb to the top of the learning curve” for full blown multi-off camera flash technique. There is a discussion in the PFRE HDR & Blending discussion group on this subject. I’ve been doing some experimentation with this technique so here’s my summary of how to bracket with flash:
- Setup your bracketing as normal (on a tripod, aperture priority and exposure bracketing -2,0,+2) except add a manual off camera flash. For the shot above I used a Nikon SB-80dx triggered by a Cactus V2 Wireless flash trigger. The transmitter end of the Cactus trigger was in the hot shoe of my Canon 5D MkII with it’s trigger cord plugged into the 5D’s PC connector. The SB-80dx had a Cactus receiver connected to it.
- Set the drive mode to single shot so that you have to release the shutter for each of the three bracket shots. This is to make sure that the flash has time to recycle between each bracket shot.
- Use a remote shutter release so you don’t have to touch the camera body. I used the Canon TC-80N3 although you could probably get by just touching the shutter release button if you are careful and your tripod is sturdy.
- Aim the flash either towards the ceiling, a blank wall or the joint between the ceiling and the wall so that the light from the flash creates a large, soft fill light. On my example above I had the SB-80dx sitting on the top of a media cabinet, camera right, pointing at the ceiling. The ceiling is diffusing the light out in all directions so their aren’t many shadows.
- Adjust the power on the flash manually (some where between 1/8 and 1/1 – same power for all three bracketed shots) so that you get a good set of 3 histograms (you want the histograms high but not clipped histograms together to fill up the available histogram space. -2 will be left, 0 will be center and +2 will be right). See Dan Achatz’s description in the PFRE HDR & Blending discussion group.
To summarize: this technique adds the same constant level of fill flash with a single flash, to each of the three brackets you shot. This fill flash is improving the quality of the light so that the whites are whiter and the blacks are blacker. This same technique works similarly with either brackets used for HDR processing or brackets processed as Exposure Fusion (EF).
For those that are already shooting brackets with flash I’m sure you’ll be able to add refinements or variations to this technique.