Long Exposures

Photography & Video

August 23, 2008

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August 23, 2008

When you get bored taking “normal” photographs, one technique that you might try is taking long exposures. It is an interesting part of the art of making photographs because you can change time, taking something that happens over a few seconds, minutes or hours & showing it all at once. This is a photograph of Main Street, on Nantucket Island, MA. It is a 20 second exposure at f: 16 & ISO 100. Although I shot this with my D200 & a 17mm – 35mm zoom lens, as long as you use a tripod there is no reason any point & shoot camera that allows aperture priority or manual exposure modes can’t do the same. If you would like more information about the modes your camera uses, check my earlier post – Camera Modes.

By the way, this image also shows (or doesn’t show) another use of long exposures. There were a number of people walking on the street at the time I took the photograph. Because they were all moving, they were never in one place long enough to appear in the 20 second exposure but the background, because it doesn’t move shows up. The automobile lights are bright enough that they show up as streaks. Long exposures are a useful way to remove moving objects from your picture.

A very typical use of long exposures is to blend moving water. Some examples:

This a photograph of the Chittenango Creek at the Chittenango Falls State Park in New York. It was taken at f: 25 and 7 seconds & an ISO of 100. The long exposure blurs the water & turns the surface bubbles into streaks. I have more images of the falls at Chittenango and those at Ricketts Glen (the next image) as well as many other waterfalls on my waterfall web page at Lakeshore Images. If you want some further examples of exposure times, those shot digitally will have the EXIF data in the large version of the images.

Next is a shot of one of the waterfalls at Ricketts Glen State Park in PA. By the way, if you get a chance, this is a beautiful park for photographers interested in taking pictures of waterfalls. There are 22 waterfalls along a pair of trails. If you have someone with you willing to drive to the bottom & pick you up (twice since the falls are divided between two trails), the walk is all downhill! Just plan your trip for a little earlier in the season. I did these & the others on my waterfall page in mid August – I would have liked a little more water going over the falls.

This image was made with a Coolpix 990 Point & Shoot camera (by the way, a 3.34 megapixel camera) – 2 seconds @ f: 9.9 & ISO 100. As long as your point and shoot camera can be set in the manual mode, long exposures are possible. During bright daylight it may be necessary to add a neutral density filter to cut down the amount of light, but a ND filter can be added to almost any camera. In this case a large ND filter was hand held over the camera lens. I’ll provide some more technical information at the end of this article.

While long exposures can be useful to give a dreamy quality to moving water, it can also be used to show movement of many things. This first image of a ferris wheel looks OK against the fading skylight behind it & provides a nice reflection on the water, however it is rather static. It is still a long exposure – The camera was a Nikon D200 using a 70mm – 200mm zoom lens, shot at f: 9 & a shutter speed of 4 seconds.

The second image was taken later that night when it was dark enough for a longer exposure. Same camera and lens, but the exposure time was 10 seconds at f: 22. Which is better? That, of course, up to the viewer, but the long exposure shows an interesting image that is not possible in real time. By the way, it is possible to end up with an exposure too long to be interesting. I have a version of this that turned to mush – the exposure was around 50 seconds. This is one of the wonderful advantages of a digital camera compared to film. You can look at your results while still at the location and retake the image if the first one didn’t work. The only solution if you are shooting film is to take a large number of bracketed exposures & hope that at least one of them gives you the results you are looking for.

There are still some cases where film is better than digital. If you take very long exposures (hours vs minutes) film has some advantages. Digital sensors do not react well to very long exposures. Electrical noise becomes a problem when the amount of light energy hitting the sensor is close to the background noise produced by the electronics. Combining low light levels with the electrical noise created by long exposures produces the worst case for digital. This is an example of a long exposure gone wrong! Click on the image to see the full size version & you can see the noise created by the combination of low light & long exposure. There are solutions – many DSLRs can be set to take a “noise reduction” image; a second exposure with the shutter closed is made immediately after the original. Since the conditions were the same for both, the electrical noise should be the same in each. The noisy pixels in the second image are subtracted from the first image, resulting in a much cleaner image. One point – for the best results, the camera should be left in the same conditions during the second exposure (which will be as long as the first). In cold weather you might be tempted to pick it up & move indoors, but the additional heat will have an effect on the noise reduction.

The first of these two “Star Trail” images is a 2 hour plus film image; the second a 1 hour and 7 minute digital exposure at f: 2.8 & using in camera noise reduction. They were not taken at the same time, in fact the film image was made in 1996 under the clear skies of Utah, while the digital image was made this week on Nantucket under good, but not completely clear conditions, and lots more ground light. Although it is not fair to compare them since they were shot under very different conditions, I still like the film version better than the digital version. Another advantage of older film cameras is they have mechanical shutters. Modern film or digital cameras use electronics to keep the shutter open – you may find your maximum exposure time (when working with multiple hour length exposures) is limited by battery life. The mechanical shutter on that old Nikon F2 or other older camera is ideal for very long exposures. When using film for long exposures you will have to deal with reciprocity problems – film emulsions are designed for a specific range of exposures; shoot faster or slower & exposures are no longer linear & color response changes. I don’t expect you to go out and purchase a film camera just to shoot “Star Trails”, but if that old camera is sitting in a closet somewhere it might be worth pulling it out to make an attempt.

As to aiming your camera, the stars will circle around the North Star (at least in the northern hemisphere), so first you need to find it (Finding the North Star). Position your camera & aim it so that the circle ends up in the location you desire. It helps to include some earth bound scenery, however be careful of any light, including the moon – it does not take much to completely destroy the faint starlight.

A last couple of examples – Making objects disappear. The first image was taken at 1/250th of a second at f: 4.5, ISO 100. The second was taken a few seconds later with a shutter speed of 5 seconds & f:22. Although I couldn’t completely remove the people on the beach because some of them didn’t move all that much, those walking & the moving boat are gone. Although I don’t have a copy here and couldn’t find a link to a posted version, I saw a wonderful image of the Golden Gate Bridge with absolutely no traffic – it was made using a long exposure to eliminate all the moving objects. Long exposures of moving objects can create some amazing images. Again, you will need a ND filter to make these during daylight conditions, and, of course a tripod, but they are well worth experimenting with.

Don’t forget the opposite of trying to make objects disappear – a very bright source of light moving during a long exposure can provide interesting results. The next time you have access to a sparkler, try a long exposure while moving it through the frame.This is the same technique used to take pictures of fireworks, lightning, and other short bursts of light against a black sky. As long as the background is black, it isn’t recorded, so long exposures only record the light. You can build layers of fireworks bursts by leaving the shutter open for 3 – 5 seconds.

I’ll save another interesting long exposure technique for an individual post – “Painting with Light.” The technique involves going out at night with a powerful flashlight, setting your camera on bulb (locking the shutter open) and moving the flashlight over the field of view.

Some suggestions for making long exposures:

Set your camera for the lowest ISO possible.
Although you may be tempted to use the smallest f: stop available, most lenses start to lose image quality when stopped down all the way. If possible, shoot for the middle range of your lens – typically f: 5.6, 8, 11 or at most, f: 16.
If you follow suggestion 2, you will only be able to take pictures after dark. The solution is to use a neutral density filter. For more information about ND filters, check my post “Camera Filters“. If your camera lens does not have threads designed to attach a filter, you can improvise. I have hand held filters in front of P&S cameras; you can also purchase adapters from Cokin & others that hold them for you. The ND filter cuts down the amount of light entering the lens by as many as 6 stops, letting you increase exposure time.
Use a tripod.

Again, shooting long exposures can be fun – get out & try some!