Set the camera securely on a tripod. If you’re using a cable release, now is a good time to attach it.
Setting the correct exposure
First, set the correct exposure using the camera’s exposure meter without the ND filter, make sure you set your ISO to the lowest it can go and the aperture to the smallest you’re happy using as this will give you the slowest possible shutter speed without the ND filter attached.
Attach your ND Filter
Screw the ND filter onto the lens. If you’re using a filter holder and square filters, attach the filter holder to the lens.
How to tell how many stops your ND filter helps to cut out
Figure out how many stops your ND filter helps to cut out, this will either be noted on the box or you can use this grid (see the grid in full in the ‘A bit of theory’ section) to look it up.
Figure out the correct shutter speed
Figure out what the correct shutter speed should be, you can either try and figure this out yourself or use a calculator tool such as the one in the Triggertrap app.
This is easy if you’re using a low density ND filter, simply double the exposure time for one stop, double it again for 2 stops, again for 3 stops and so on.