The general approach I use with ND filtration is to compose and meter your scene first without filtration. I also use the Lee filter holder, which has the handy feature that allows you to clip/unglip the actual filter holder to/from the lens adapter fairly easily. The general process to expose for any amount of ND filtration, including the Big Stopper or other large-stop filter, would be as follows:
- Attach the Lee filter adapter ring to lens. Set camera to Manual mode.
- Fully meter the scene at a fixed ISO of 100:
- Evaluative metering will work well with average scenes of relatively balanced tonal range. (Make note of shutter speed.)
- Selective spot or partial metering will often be necessary with scenes of divided contrast or uneven tonal range. (Make note of shutter speed.)
- If you are also using Graduated ND to compensate for contrast, meter highlight, midtone, and shadow areas to determine total dynamic range
- Set aside the shutter speeds for graduated compensation in a later step.
- Compose scene in-camera without filtration.
- Adjust aperture here if necessary for artistic/stylistic effect.
- Apply ND filtration and compensate shutter speed:
- Multiply the shutter speed by the filtration factor:
- This is easy to calculate. Take 2 to the power of the number of stops of ND filtration:
- If applying a 2-stop/0.6 ND filter, multiply shutter speed by 22, or 4
- If applying a 10-stop/3.0 ND filter, multiply shutter speed by 210, or 1024
- Apply Graduated ND (GND) filtration (Optional):
- GND filtration should not be compensated for in-camera, as the intent is to mitigate highlights for a given exposure.
- The amount of GND filtration necessary in stops can be computed as follows:
- Divide the longer shutter by the shorter shutter.
- Take the log of the shutter speed quotient
- Divide the first log by log(2)
- Apply white balance correction (Optional):
- If you are using a considerable amount of ND filtration, strong color casts may appear
- These can be corrected in post, however they are often EXTREME, and may not be fully correctable
- To ensure viable correction in post, compensate in-camera first (according to manufacturer's recommendations and settings)
- Lee BigStopper tends to cast very, very blue...so set WB to around 10k or more
- HiTech 10x ND also tends to cast rather blue, so a setting near or even above 10k might still be needed
- Other brands may cast very magenta or violet-blue, some cast very green or yellowish
If you have a smartphone with a calculator, computing these is extremely easy in the field. You can also try to memorize a few things to help you quickly arrive at rough settings without the need to use a calculator. Here is a table of ND stops filtered to shutter speed multipliers (Ratios provided for Lee/Singh-Ray filter users...just add up all the fractions of your ND filter stack):
ND Stops | ND Ratio | Multiplier
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x1 | 0.3 | 2
x2 | 0.6 | 4
x3 | 0.9 | 8
x4 | 1.2 | 16
x5 | 1.5 | 32
x6 | 1.8 | 64
x7 | 2.1 | 128
x8 | 2.4 | 256
x9 | 2.7 | 512
x10 | 3.0 | 1024
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Example Scenario #1: Simple ND filtering
You wish to photograph a serene river scene, completely blurring out not only the motion of water, but also the slight rustling of the leaves of the trees, creating a very dreamy style of photograph:
- The scene has roughly even tone, no GND filtration is needed
- You use evaluative metering, and compensate down by 1/3rd of a stop
- Aperture f/8
- ISO 100
- Shutter meters at 2 seconds
- You want to apply 6-stops of ND filtration (1.8 ratio)
- Shutter speed needs to be increased by a factor of 64: 128 seconds, or about 2 minutes
Example Scenario #2: Complex ND+GND layered filtering
You wish to photograph a cloudy coastline just after sunset, blurring the soft waves to a fog and flattening clouds. You need to compensate for the sun, which is just below the horizon and brightly illuminating the sky relative to the sea.
- The scene has high contrast, so GND filtration is necessary
- You spot-meter the sky near the sun, and get an exposure of 1/50th second
- You spot-meter the sea near the horizon, and get an exposure of 1/3rd second
- You spot-meter the rocky coastline, and get an exposure of 1 seconds
- Total difference in stops between the sea and sky: @4 stops
- log(1/3rd / 1/50th) / log(2) =
- log(.3333 / .02) / log(2) =
- log(16.6667) / log(2)
- Total difference in stops between the sea and coast: @1 2/3 stops
- log(1s / 1/3rd) / log(2) =
- log(1 / .3333) / log(2) =
- log(3) / log(2)
- (Check) Total difference in stops between sky and coast: @5 2/3 stops
- log(1s / 1/50th) / log(2) =
- log(1 / .02) / log(2) =
- log(50) / log(2)
- Three levels of GND filtration necessary:
- One 2-stop soft grad filter for the division between coast and sea
- One 3-stop and one 1-stop hard grad filter for the division between sea and sky
- Alternatively, drop the extra 1-stop hard grad if you are worried the sky may end up too dark with an additional 10-stop filter, or you intend to slightly under-expose to preserve highlights
- You use center-weighted or partial metering on the sea:
- Aperture f/8
- ISO 100
- Shutter meters at 1/4th
- You want to apply a 10-stop BigStopper (3.0 ratio) or similar ND filter
- Shutter speed needs to be increased by a factor of 1024:
- 1/4s x 1024 / 60s/m =
- 0.25s x 1024 / 60s/m =
- 256s / 60 s/m =
- 256 second or 4m 16s exposure time