What ND filter strength do I need for daytime lightning long exposures?

Question

I’m new to photography and have managed a decent lightning photo at night using a long exposure. In daytime, though, my exposures are too bright to leave the shutter open long enough to catch lightning. A friend suggested using a neutral density (ND) filter.

I’m shooting with a Canon 600D and the 18–55mm kit lens. Is an ND filter the right approach for daytime lightning, and how do I choose the correct strength?

user37321 · Answer

The differences between ND filters are not necessarily between kinds but rather between values.

The value you should look for is how many f-stops (or in this case shutter speeds) do you want to change.

Let's say the light conditions you are taking the photo in now (9AM, with sunlight, in summer, your iso and aperture well defined) give you a shutter speed of 1/500 and you need a exposure of 1/2 second.

The f-stop difference will be

1/250=1

1/125=2

 1/60=3

 1/30=4

 1/15=5

  1/8=6

  1/4=7

  1/2=8

So you need a filter that reduces the light 8 f-stops.

According to this table http://en.wikipedia.org/wiki/Neutral_density_filter you can use a ND108 or N119 filter.

It is not recommended that you stalk too many filters, but probably 2 will be fine, so you can buy for example a 103 and a 106 and combine them to have a 109.

Polarizing filters are helpful and they have an Xx scale to see the f-stop change. A filter that is marked 2x will reduce the f-stop 2 steps.

What ND filter strength do I need for daytime lightning long exposures?

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