Long exposure: how an ND filter clears crowds
While you can achieve a long exposure easily at dusk and dawn, what if you want to use a long exposure during the day? The trick is to get yourself a strong ND filter (neutral density), which cuts out nine or 10 stops of light.
A long exposure can create milky water effects and is great for waterfall pictures, as well as blurred clouds in when shooting landscape photography; but that isn’t their only use. A long exposure is also handy for making moving subjects ‘disappear’ when you shoot buildings, street scenes or architecture. Sometimes it’s great to include people in a scene to give a sense of scale or location, but they can be distracting if you want a clean composition.
The shutter speed you’ll need for this long exposure technique depends on how quickly the subjects are moving.
For fast subjects such as cars or people very close to the camera, you can get away with a shutter speed of a couple of seconds, but for street scenes with people that are far away you’ll need to use a long exposure of at least 10 seconds. This is where the very strong ND filter comes into its own…
How to use a long exposure and an ND filter to remove crowds
01 Reduce noise
Long exposures can create noise in your images, so before you start, enable Long Exposure Noise Reduction in the Shooting menu settings. Scroll down to the ‘Long exp. NR’ option and use ‘OK’ on the control pad to switch it to on.
02 Keep it stable
If you’re using long shutter speeds, you’ll need to securely attach the camera to a tripod to avoid any possibility of camera-shake. Make sure the legs of the tripod are stable, and avoid using the centre column if you can. Use a remote release or self-timer to fire your digital camera.
03 Compose yourself
Once you attach the filter, it’s very difficult to see clearly through the viewfinder. This means you need to get your composition spot-on beforehand. Focus manually and set the focus to suit the subject. For most subjects, you’ll find setting the focus to infinity will be fine.
04 Set your exposure
With the camera in position, set the aperture to a small setting, such as f/16, and take a meter reading. Adjust the shutter speed accordingly, and take a quick test shot to make sure the scene is exposed correctly. For our scene, the exposure was 1/30 sec at f/16.
05 Add the filter
Neutral-density filters come in two types: a drop-in square system such as those from LEE and Cokin, or a round screw-in type such as those from Hoya and Light Craft Workshop. Whichever type you use, don’t move the camera or the focus setting when attaching the filter.
06 Adjust the exposure
With the filter in place, you’ll often find that the meter won’t work properly, so you’ll need to adjust the shutter speed to take account of the strength of the filter you’re using. For our scene, we needed an exposure of 15 secs at f/16 using a nine-stop ND filter.
ND Filter Numbers
Different brands use different numbering systems to indicate the strength of their ND filters. When it comes to the very strong models there are two commonly used systems.
The easiest to understand tells you how many stops of light the filter will reduce the exposure by, so you’ll find the filter described as a nine- or 10-stop ND. The other numbering system uses the filter factor, or how much you have to multiply the exposure by when using the filter.
For each stop of light that the filter blocks, you need to double the exposure time, so for a 10-stop ND filter, multiply the exposure by approximately 1,000.
on Friday, March 9th, 2012 at 11:33 am under Photography Tutorials, Tutorials.
Tags: architecture photography, camera tips, digital camera, hot, long exposure, ND filter