I’ve had a few people write me asking about Ambient Light and under 3 stops. So, let's delve into this subject of ambient light and under or over exposing with a flash.
Without a flash point the camera at the subject. I have my camera set for Matrix Metering, Aperture Priority and this gives me a reading of f/3.5 with 1/10 shutter speed and ISO 200.
Step One: Get An Ambient Reading
You need a starting place to be your base exposure. Everything else will relate to this exposure. I took a picture of the top of my Nikon D3S with a 28-300mm Nikkor lens. I just pointed across the room for this example. With ISO 200 I have f/3.5 aperture at 1/10 shutter speed. This is my Ambient Reading with no flash.
Step Two: Use your Nikon SB900
You can use whatever hotshoe flash compatible with your camera manufacturer, but it must be a TTL flash or this will not work as easily.
Step Three: Slow or Rear Curtain Sync
You need to set your flash setting as I have done in the above photo to Slow or Rear Curtain Sync. This tells the flash and the camera to “please use the Ambient setting on the camera and then add the flash to the exposure without over exposing the photo”.
Fill Flash normal setting (Nikon D3S, ISO 12,800, f/5.6, 1/20, 28-300mm)
Take a photo with this setting as I did in the photo above here. This will basically light everything up. I am bouncing my flash with the diffusion dome on the flash for this photo. It’s still getting light from the window, but the flash is filling in everything closest to the camera. The background is brighter, but since it is further from the flash it is not as bright as the statue.
Step Four: Adjust the flash power under 3 stops
I choose 3-stops under, because it’s the lowest one can go with TTL mode, where the camera will figure it all out for me.
On the Nikon SB900 you push the button in the far upper left. It will cycle all the way through under and over exposures. Stop on the -3.0 EV. EV stands for Exposure Value.
With the camera not changing the setting and then telling the flash to underexpose by -3.0 stops you get the underexposure results.
You can also adjust the camera exposure and the flash exposure and get even more results. Experiment around with the ambient and underexposure flash…it’s fun to had a calculated surprised.