This is the 45th in a series of posts on the Fujifilm GFX-50S. The series starts here.
The GFX offers an all-electronic shutter, which Fuji calls ES in the menus. I’ll do the same here. We have seen here that the shutter takes 1/4 second to complete an exposure. This can cause horizontal bands (in landscape orientation) when the subject is lit by lights that change intensity during the exposure. Many fluorescents and light-emitting diode (LED) lights do that. The lights that are today replacing the nice, steady incandescent illumination typically have variations at twice the line (or mains, if you speak British) frequency. In the US, that’s 60 Hz, so the cycle of the lighting is usually at 120 Hz. In Europe and Britain, the mains frequency is 50 Hz, and the lighting flickers at 100 Hz.
Not all LEDs flicker. The ones that are made for photography usually show no noticeable flicker, or flicker at frequencies well above the power line frequency. Modern LED stage lighting often flickers at frequencies unrelated to the power line.
In the olden days of film photography and cathode ray tubes (CRTs), we sometimes had to get a picture of, say, a TV set in out images. If we weren’t careful, the scanning of the CRT would be visible in the photograph, which was usually unwanted. Since the CRT was scanned at a frequency close to, but not the same as, the mains frequency, the conventional wisdom was to set the camera shutter speed to one or two power line cycles so that every place on the screen had a chance to go through an integral number of scans. In the US, the magic shutter speeds were 1/60 and 1/30 second, and in Europe, they were 1/50 and 1/25 second. In practice, this sort of worked. The shutters of the day were not sufficiently accurate for a perfect fix.
The scanning of the digital sensor by an electronic shutter is an analog of the raster scanning of a CRT, so the same idea should apply. I’ve been dealing with the electronic shutter in the a7RII for some time now, and I never thought of using this method since it was so hit-and-miss in the film days. But modern shutters are much more accurate than the old all-mechanical ones. Yesterday I saw a DPR post that made it appear that they are accurate enough to make this method work.
I had to run a test for myself.
I photographed a LED-illuminated light fixture with the GFX and the Fuji 63 mm f/2.8 lens at various shutter speeds. I developed the images in Lightroom, performing white balance to taste and adding a +100 contrast move to emphasize the banding. I live in the US, so the magic shutter speeds should be 1/125, 1/60, and 1/30 second. As you’ll see, they all work fine. In addition, the effect diminishes at the shutter speeds get longer.
Here are the images:
You might ask how accurate are the power line frequencies. They are very accurate — far more accurate that your camera’s shutter — for reasons totally unrelated to photography. It used to be that electric clocks had synchronous motors, and the power line frequencies determined the accuracy of those clocks. Then came along modern interconnected electric grids and it became an operational necessity for everybody to adopt the same power line frequency (and, to some extent, even the same phase).