If you’re anything like me when it comes to fitting a neutral density filter to the camera, you’ll probably scratch your head for a while before eventually choosing the closest filter in the bag, which of course is never the right one and ends up flying from your hand and rolling down the nearest hill as you fumble to replace it with a more appropriate filter buried deeper in the bag somewhere. Sound familiar….?
This table might help, just look up your shutter speed in the green column, and scan across to the resulting shutter speed with an ND filter fitted to see which ND filter strength results in the shutter speed you’re after. Feel free to print a copy and keep it in your camera bag. I’d much prefer a printed table than a phone app for this sort of thing, it’ just simple. A table like this can also help if you’re intending to purchase ND filters and need to figure out which one’s a good fit.
Another option is to do a little maths in your head using the filter multiplication factor, but that’s not always straight forward when thinking in fractions of a second, but with practice can become the quickest way. If you use ND filters regularly, you’ll probably know which to select for a given situation without even thinking about it, it comes down to familiarity.
If you’re not familiar with neutral density filters, here are a few quick tips:
- They’re usually designated by the number of stops of reduced light, one stop being a halving of light.
- A three stop ND filter for example (ND3) will reduce the light three stops, which results in a shutter speed eight times longer (2 x 2 x 2 = 8).
- They can also be designated by a multiplication factor, which is usually easier to figure out in your head.
- A six stop ND6 filter has a multiplication factor of 64 times, so a one second exposure would become a 64 second exposure, as you can read in the table.
- A 10 stop filter has a multiplication factor of about 1000x, so on a bright day, so a shutter speed of 1/500th of a second would become 2 seconds with the filter fitted.
- You can also adjust the camera aperture or ISO to fine tune the shutter speed, you don’t need every single variation of ND filter.
- A polarizing filter reduces the light by about 1 or 2 stops.
- Filters can be stacked together, though I’d try to avoid that as each layer will reduce the optical purity a little.
- Also consider the changing light, at dawn or dusk the light level changes fast and you’ll want to plan ahead.
If you have any ideas on how to improve the chart please send them through.