How to Use a 10-stop ND Filter to Take Long Exposure Sunset Images
I used my B+W 10-stop the other day to do some long exposures at sunset and thought I’d write up the steps I took to get the shot.
Firstly for those of you who aren’t familiar with this type of filter, it’s basically a very strong neutral density (ND) filter which reduces the amount of light hitting the camera’s sensor by about 1000 times. ND filters are very common but they are typically only 3-stops in strength (reducing the amount of light by 8 times) so a 10-stop one is quite extreme.
The first thing I did was find a suitable composition as I would for any shot. I wanted to achieve the misty water look so I found some rocks with water washing over them and composed my shot. Note it’s vital to use a tripod with these shots due to the long exposures.
Once I had the shot composed the next step is to work out what exposure will be needed. At this point I usually take a test shot without the ND filter and then multiply the shutter speed by 1000. e.g. if using aperture priority, ISO 100, f/11, the shutter speed is 1/50, then the required shutter speed with filter would be 20 seconds (.02 * 1000).
In this case however I was a bit lazy and decided to just put the filter on and take some test shots to work out the exposure.
As it was nearly sunset, I also needed to use a graduated neutral density (GND) filter to balance the exposure between the sky and foreground. Positioning the GND filter when also using a 10-stop ND filter is difficult because it’s hard to see anything with the ND filter on. Luckily my Canon 7D’s LiveView allows me to ‘see through’ the ND filter so I used this when positioning the GND. My 40D didn’t allow me to do this so I had to position the GND filter on first, take it off the camera (while still in its holder), screw the ND filter on, and then put the GND filter back on. A bit time-consuming as you can imagine and so much easier using LiveView!
Here’s the first shot I took.
ISO 200, f/9, 30 seconds
Not bad, but a little underexposed (you can see the rocks are too dark). The settings I used were just based on experience from previous shots I’d taken using the filter. There’s also a bit of vignetting caused by stacking filters on a wide angle lens. Larger GND filters can avoid this but since I only have Cokin P-sized ones I decided to zoom in slightly (11mm vs 10mm) to minimize vignetting.
This is the final shot I took and the one I think I will keep:
ISO 400, f/9, 60 seconds
Since the sun was lower in the sky I needed an even longer exposure. I decided to use ISO 400 to keep the exposure down to 60 seconds. Sometimes noise can be a problem at higher ISOs but my 7D handles ISO400 just fine.
Note the only processing done on the above shots is converting from RAW to JPG and applying camera’s Landscape picture style. Other processing steps I would take include straightening of horizon, local exposure adjustments if needed, white balance, sharpening, noise reduction etc.