I admit it; I'm a gear head. I love my photography equipment, or course, but I'm also rather fond of my smart phone, my personal computer, and the other sundry electronic gizmos and gadgets scattered throughout my house. I don't think I'm alone in this regard. Do a search in Google images or Flickr on the term "iPhone" or "Nexus" and you'll find thousands and thousands of images taken by photographers of every level of expertise. Some of these images are quite remarkable and could easily stand in for the press photos distributed by Apple or Samsung. Others are…well...somewhat less remarkable. A particular problem with many of these photos arises from poorly balanced exposure; either the subject's screen appears dim and washed out or the screen is bright but everything else in the photo is too dark.
In this post I'll discuss an approach to lighting and photographing gadgets with backlit displays using a DSLR (or any camera with manual shutter/aperture controls), a tripod and a flash. While the focus of this post is somewhat specialized, it also serves to illustrate a much broader and incredibly useful photographic technique -- balancing exposure from flash and continuous light sources. I'll return to this broader issue many times in future posts.
Two exposures in one
The key to balancing exposure from flash and continuous light is recognizing that you're effectively creating two exposures at once. The flash provides a burst of light that is very bright but also very brief. Because a typical flash duration is on the order of 1/20,000th of a second, your camera's shutter speed is largely irrelevant to the exposure from the flash. Continuous light sources such as the backlight on an LED display are not nearly as bright as a flash, but they contribute to a photograph's exposure over the entire time the camera shutter is open. Thus, you can think of a photograph exposed by a mix of flash and continuous light as a composite of two exposures. The brightness of the flash exposure depends on the power of the flash and the lens aperture, while the brightness of the continuous exposure depends on the power of the continuous light source, the lens aperture and the camera shutter speed.
To photograph a device with a backlit display, I recommend using flash to expose the body of the device and the background, while relying on the screen backlight to expose the screen itself. Start by placing your camera on its tripod and positioning the subject and flash. Focus the camera, then turn autofocus off and dim any room lights that might contribute to the exposure. To dial in the flash exposure, pick an ISO and set your shutter speed to your camera's max flash sync speed (usually 1/200th or 1/250th of a second). Ignoring for the moment the look of the screen itself, adjust your lens aperture and/or flash power until your subject is exposed the way you want it. Now, with your camera fixed on its tripod, dial down your shutter speed. If you take a sequence of photographs at increasingly long exposures, you'll see that the backlit screen of your subject appears to get brighter and brighter even though the exposure of the subject and background does not change. Pick the frame that most appeals to you.
The sequence of images at left illustrates this approach. Except for cropping, these images are all straight out of the camera. Each was taken at ISO 400 and f/7.1 with a single flash in a softbox from camera right. I positioned a white card opposite the camera to reflect a triangular highlight in the upper left portion of the iPhone's screen. The only variable that changed from frame to frame was the camera shutter speed, which determined the brightness of the backlit screen. I personally like the 1/30th second exposure best, but your milage may vary.
Fun with reflections
You can add interest to your photos by arranging your composition to include reflections in your gadget's screen. Simple highlights, like the ones in the iPhone example above, help to convey whether the screen has a glossy or matt surface. If the screen is glossy then it can act like a mirror and the reflected image may be the actual subject of your photograph. As before, anything that you intend to be reflected off the screen should be lit by your flash so that you can independently control the brightness of the reflected image and the backlit screen.
Here's a lighting diagram for the image up top. I placed my camera on a tripod and sat down in front of the iMac. I angled the Mac's notoriously glossy screen so that I could see my camera reflected in it, thereby ensuring that the camera could also see me. I lit myself with a single flash from camera right and adjusted the camera's shutter speed to balance the brightness of the reflected image and the backlit display.