It's amazing what you can do with a ND 400!
The ND 400 is a neutral density filter which reduces dramatically the intensity of light entering the camera (loss of 9 stops), which allows long exposures at any time of day.
So, during a sunny day on a beach, you can consider images with exposure time up to 30 seconds easily. Everything that moves during the long exposure time will blur or absent from the photo (clouds, water, waves, people,...)!
However, due to the very low light entering in the camera, most of DSLR's automatisms do not work (autofocus and light metering). The use of ND 400 is quite delicate and requires many manipulations to achieve his ends.
The basic technique
- Mount the camera on a tripod (essential accessory for this kind of photo) and set sensitivity as low as possible (eg ISO 100)
- In "Aperture Priority" (Canon Av mode) set an aperture of f/11 (to have a good depth of field while maintaining good image quality)
- Compose your photo
- Make the focus, the measurement of exposure, and note the exposure time (eg 1/60 s)
- Turn off your autofocus
- Attach the ND 400 filter on the lens
- Switch to "Manual" (Canon M mode) and adjust the speed value / aperture
- keep the same aperture (eg f/11)
- use a time speed corresponding to your initial measurement -9 EV (eg : 1/60 s gives a value of 8 s)
- Shoot with a remote control (again, almost indispensable accessory to avoid camera shake)
- Reflex offer some options to minimize blur due to vibrations (displacement of the mirror at the shooting).
- A long exposure increases the digital noise on the picture. Reflex offer some options to reduce this noise. Remember to enable or disable these options to suit your needs and results, knowing that the DSLR need a fairly long time (equivalent to the exposure time) to limit noise on the picture.
- Think to shoot in RAW format (instead of JPEG). With software like Lightroom or DPP, this will allow you to correct the defects of exposure or white balance (the ND 400 have a tendency to derive the color to blue-magenta).
- The modern digital SLR allow to use the rear screen and provide an « exposure simulation » function which displays and simulates how the brightness of the actual image will look.
This feature greatly simplifies the use of ND 400 filter, the rear screen then allows you to setup speed, aperture and focus, and seeing the results on the screen, even with the ND 400 mounted on the camera lens!
It is not always easy to calculate the speed value to use depending on the initial metering without the filter. A simple method is to have a table of EV (Exposure Value).
In my example, the couple f/11 – 1/60 s at 100 ISO gives an EV 13. The ND 400 is going to move to EV 4 (-9 stops), which gives the speed value to use, here 8 s.
Here are two sites where you can find and print tables of EV at 100 and 800 ISO: