Long Exposure Photography

Long exposure or slow shutter photography involves the use of shutter speeds much longer than for standard photography, often minutes or even hour long exposures. Long exposure photography can create images that are otherworldly, full of detail and allow us to document things such as stars, movement and effects that we wouldn’t usually see. Long exposures also allow us to use techniques such as ‘painting with light’.

Image of the Severn Bridge Long Exposure Night
Severn Bridge, Gloucestershire 120 seconds @f/8 ISO 100 105mm

The image above of the Severn Bridge was taken with the camera on a tripod, using a remote release to give an exposure of 2 minutes, the aperture was set at F/8 to prevent the shutter time becoming prohibitively long and to maintain some details in the water rather than it becoming completely fog like.

When photographing moving water, the longer the exposure the more blurred the water will become until it is completely smooth as in the image of the Pier below:

South Shields Pier 25 seconds @f/18 ISO 100, 10 stop Neutral Density (ND) filter 80mm lens

To achieve the long exposure in daylight, a 10 stop or 1000ND Neutral Density filter was used. A neutral density filter is a grey filter that should have no discernible effect on the colour in the image and can be bought in a variety of strengths, 10 stops is one of the strongest ND filters available. 10 stop ND filters can be found at varying prices on Amazon. A £20 filter may not be as robust as a more expensive filter, but it will get you started in long exposure photography.

Milky Way over the Grampians National Park, Victoria, Australia 20 seconds @f/2.8 ISO 3200 17mm lens

The photograph of the Milky Way above was shot with an exposure of 20 seconds. If the exposure is too long movement will be visible in the stars, as a guide approx 20-30 seconds is the limit to freeze the stars.

For a better calculation of exposure dependent on your equipment, you can use the 500 Rule to calculate the ideal exposure: Exposure time = 500/[crop-factor × focal length]. For example: 500/[1.0 (Full Frame) x 24mm (focal length)] =500/24= 20.83 seconds, you then need to adjust the ISO and aperture to achieve that shutter speed.

Once the exposure goes beyond this, the stars will become star trails. In theory you can shoot very long exposures to achieve long or full star trails, however the noise levels in the images become objectionable with very longer shutter speeds and combined with the high ISO for star photography. To reduce this multiple exposures one after the other can be used and the resulting images stacked in Adobe Photoshop or other software. Some modern cameras now have inbuilt stacking ability.

Star Trails, Isle of Harris, Outer Hebrides 365 seconds (Approx 6 minutes) @f/4.2 ISO 3200 11mm lens