Calculate long exposures
take A test exposure
Extreme ND filters such as the LEE Big Stopper (ten stops) are too dark to meter and focus with the filter in place. You therefore need to compose and focus without the filter and take a test shot to establish a ‘base exposure’.
Shooting long exposures isn’t difficult, but you will need to do some maths
calculate the filtered exposure
You can do the maths (double the exposure time for each stop) or use an app such as the exposure calculator in PhotoPills. Here, an exposure of 1/10sec at f11 and ISO 100 ‘translates’ to 102 seconds with the Big Stopper.
take the final shot
Fit the filter and switch to manual focus so the camera doesn’t attempt to refocus. For exposures of longer than 30 seconds, switch to Bulb mode and use a remote release to lock the shutter open for the calculated time.