D500 Electronic Front-Curtain Shutter Analysis
I did a little analysis of the effectiveness of the “electronic front curtain”, or EFC, on the Nikon D500. The EFC is a feature presently available only on Nikon’s high-end cameras, and only available with “Mirror Up” (Mup) mode. When using EFC, the front curtain of the shutter doesn’t move during the exposure, and therefore doesn’t cause any vibrations.
EFC camera menu
Nikon D500 User Manual EFC explanation
Is this feature one of those marketing gimmicks, or is it truly useful? You probably won’t notice much effect until you get to really show shutter speeds and/or really long focal lengths, where vibrations become a severe problem.
There are two substantial sources of vibration, even when your camera is mounted on a heavy tripod. The first vibration source is the mirror, which slaps up out of the way of the shutter. Because of this, you need to either stay in Live View mode or wait about 3 seconds before tripping the shutter. The second vibration source is the shutter itself, which is divided into the sudden front shutter curtain motion, followed by the rear curtain motion. When EFC is active in “Mup” mode, the camera will open the front shutter curtain, but not electronically enable the sensor. When you trigger the completion of the photograph, the camera first electronically enables the sensor (and begins the exposure) and then closes the rear shutter curtain to finish the exposure.
To test this EFC feature, I set a Sigma 150-600mm lens on 600mm and stopped the lens to f/22 at ISO 100, so that the shutter speed was on 1/30 second. I disable lens vibration reduction during the testing. This is normally a very problematic shutter speed with this long of a lens, but my goal was to force a vibration issue. Note that vibrations are even worse around ½ through 1/15 second. I used a very heavy tripod while testing, but I know that vibrations are still a big problem when using this long of a focal length (900mm effective). I also used a remote shutter release.
I shot a resolution target at 16.8 meters, and then used the MTFMapper program to analyze the results. Since the results can vary from shot to shot, I did about 15 photos with and then without EFC active. I got measurements in both the meridional and sagittal directions, since I figured there might be a directional bias to the vibrations.
For the non-EFC mode, I ended up with an average MTF50 of 16.6 lp/mm in the sagittal and 21.3 lp/mm in the meridional directions. For the EFC-active mode, I got 23.6 lp/mm in both the sagittal and meridional directions. For the sensor target area I used for measuring the MTF, the sagittal direction was horizontal and meridional was vertical. Subject motion blur was easily visible in the photographs without EFC active; EFC really makes a difference!
The percent increase in resolution when activating EFC was (23.6-16.6)/16.6 * 100 or 42% for the sagittal (horizontal) direction, and (23.6-21.3)/21.3 * 100 or 11% in the meridional (vertical) direction. As I stated earlier, the vibrations would have been even worse at slower shutter speeds than this.
Using EFC makes a substantial difference in resolution (at slow shutter speeds or high magnifications). There’s really no reason not to enable EFC if your camera has it; note that the D500 does have a shutter speed limit of 1/2000 while using EFC mode. Again, the EFC mode is only available in conjunction with the “Mirror-Up” mode, although you can still decide if you want to use phase-detect focus or switch to Live View and use contrast-detect focus. Either way you use EFC, you still want the mirror up for at least 3 seconds prior to taking the photo.
For my camera, EFC mode is disabled by default, which I think is crazy. I’m not sure if other camera models have the same default, but I bet they do. If your camera supports it, then please, please enable EFC right now.
Sigma 150-600 at 600mm on D500. Used EFC to rid any vibrations