How to take Long Exposure Images

This is my edited version of a long exposure tutorial found at Click Here as acknowledged by me. The Lough Neagh Image is my own and is copyright.

1. Why Use Long Exposure?

Really long exposures, exposures in excess of several minutes create surreal, dreamlike images. They are mostly created using Neutral Density filters (ND), think of sunglasses for your lens to extend exposure times far in excess of what could be achieved by simply decreasing ISO and stopping down your aperture. Long exposures create a sense of mystery. They softly blur anything that moves. Clouds become streaks, water takes on a cotton candy-like appearance and people either disappear or become ghosted figures. But the most important perk to using a very long exposure is that it simplifies the composition. It strips down an image to the basics: lines, shapes, and tone.

2. Equipment

Obviously, you will need a DSLR camera, wide angle lens, tripod, cable/remote release, fully charged batteries, you will also need solid Neutral Density filters. ND filters decrease the amount of light entering the lens. ND filters allow you to slow your shutter speeds from fractions of a second to lengths in excess of several minutes, even in daylight.

Other items you might need include:

  • Exposure conversion chart or better still an app (there are lots of free long exposure apps available for your cell phone, search “long exposure calculators”)
  • Something to cover your camera to stop light leaks
  • A timer (I use my phone app)
  • A Sturdy Tripod
  • Lots of patience!
  • Warm waterproof clothing depending on the weather.

3. ND Filters

ND is short for Neutral Density, sometimes referred to as a “grey filter” or “dark glass”. A perfect ND filter should filter all the visible colours of light equally. This means that an ND filter shouldn’t have any effect on the colours in your image. Unfortunately, with very long exposures this is not always true. If you are taking exposures, in excess of five minutes, you will sometimes pick up a pink or magenta colour cast. This is because higher wavelength light (infrared) is not completely blocked by some ND filters and builds upon the sensor. Adjusting the white balance during post processing will usually repair this pink cast. In addition, many filter manufacturers now combine ND filters with IR blocking capability, but these are more expensive. To avoid this colour cast completely, many photographers choose to convert their long exposures into black and white.

NOTE: Graduated ND filters are clear on the bottom half and become darker to the top half. Graduated ND filters are used when the dynamic range of the scene is too high to record. They are often used in landscapes to darken a bright sky. For long exposure photography, you will need Solid ND filters. These filters, as the name implies, are a dark from top to bottom. You will also need a filter holder if using rectangular filters. (see below)

ND Filter Types

ND filters come in two varieties, circular screw-in and rectangular. The latter requires a holder that attaches to the front of your lens. You then slide the rectangular filter into the holder. I prefer the screw-in variety because they are easier to attach and have less chance of light leakage. When you are buying an ND filter, buy one that fits your largest diameter lens. If you have smaller diameter lenses that you would like to use the filter on, buy a step-up ring. A step-up ring allows you to couple the larger diameter filter threads of the filter to smaller diameter threads on a lens. The photo shows a rectangular graduated ND filter and Solid filter set available at Amazon.co.uk at only £14.99 it includes:-

A Neutral Density ND Filter Set ND2 ND4 ND8 + Gradual Neutral Density ND Filter G.ND2 G.ND4 G.ND8 + 9pcs Ring Adapter (49mm 52mm 55mm 58mm 62mm 67mm 72mm 77mm 82mm) + Filter Holder + Filter Case for Cokin p series for Canon, Nikon, Sony LF6

Click the photo and go directly to Amazon to order.

Screw in ND Filters are similar to any lens filter, in that they screw into the end of your lens. There are two types, fixed strength and adjustable strength. The fixed type is of a stated strength and cannot be adjusted while the adjustable types are like polarising lens filters which can be turned to adjust their strength by a ring on the edge of the filter.

The picture shows- CameraPlus – Professional 77mm Slim S-PRO1 MC Neutral Density ND 3.0 Filter 1000x – 10 Stops + Free aluminium screw-in filter caps.

Click the photo and go directly to Amazon to order.

ND Filter Strengths

ND filters are rated according to how much light they block. The darker the filter, the less light is transmitted through it. Less light corresponds to longer exposures. When you choose an ND filter you will find that different manufacturers use different systems to describe the strength of their filters but generally, the filters are rated in stops, therefore, a 10-stop filter reduces exposure by 10, 6-stop by 6 and so on. If you plan on taking your long exposures during the day, I would suggest purchasing a 10-stop and 6-stop filter. These can be stacked together to produce a total of 16-stops. A circular polarizer is equivalent to approximately a 2-stop reduction in light and can also be stacked with your ND filters. Although you can stack multiple filters together, do not stack more than two as vignetting will become very visible in the resulting images.

 

4. Subjects

When you are looking for subjects that make for good long exposure photographs, pick a scene that has both stationary objects and something that moves. The movement can be found in water, clouds, traffic and people. Here are a few examples of great subjects.
• Pilings or piers with a very low distant horizon
• Dock or harbour – be careful with moored boats “bobbing” in the water, as they will appear as ghosts!
• Tight shots of buildings showing only walls and clouds
• Wide landscapes with rolling fog or dramatic clouds
• Isolated old buildings with blowing grass and moving clouds

Old Piles2

Old Jetty Piles at Lough Neagh N. Ireland

©Christopher Cosgrove

5. Taking Very Long Exposures

Long exposures take a long time! They are the exact opposite of “point and shoot” photography. Long exposures take a lot of thought and planning before you press the shutter. NOTE: the setting up must first be completed WITHOUT the ND filter attached or if using an adjustable at the lowest stop setting. A definite must is a cable release or remote timer, imagine holding the shutter button for several minutes and you will realise why a shutter release lock is imperative.

Composition

When you arrive at your shoot location, take some time deciding where the best vantage point is. Walk around and take several regular exposures and evaluate these on the back of your camera. Should you move a bit to the left or right? How high do you want the horizon? Are there any distracting elements at the edges of the frame? Once you are satisfied with your composition, set up your tripod and attach your camera. You may still need to do a little tweaking of the composition before your final long exposure. Once you are set up on your tripod, attach a cable release or a remote timer and select the lowest ISO on your camera. Make sure that vibration reduction is turned off if it is available on your lens. Then again double-check the framing of your shot.

Choose Your Aperture

With your camera in aperture priority, select a relatively small aperture (f/8 or smaller). Apertures between f/8 and f/11 are typically the sweet spot for a lens. Assuming you are using a wide-angle lens (24mm or wider), these apertures will give you lots of depth of field and sharp focus from edge to edge. I try to avoid using f/22 and smaller apertures to minimize diffraction. Diffraction is the softness that occurs due to light bending around the diaphragm blades. It becomes much more apparent at very small apertures.

Focusing

Switch your camera to manual focus and focus your shot, this is important to prevent auto re-focussing occurring later. I usually focus 3-6 feet in front of the camera. This assures that you have both your foreground and background sharply in focus. Check your focus on the back of the camera using live view and magnification. Be aware though, diffraction may become unacceptable at very small apertures, as I mentioned above. Take a photo and check your image for focus. If necessary, readjust the focus. It is a good idea to place a piece of gaffer tape over the focus ring to ensure it doesn’t accidentally get moved once you have established focus. All of this composition and focus work is done without the ND filter(s) attached. You will find that with ND filters on the front of your lens, you will not be able to see out your viewfinder! The display will be too dark to compose, let alone focus.

Shutter Speed

The next step is to determine how long your exposure should be once you attach the ND filters. After you put the ND filters on your lens, your camera will not be able to meter. You must calculate the correct exposure based on the strength of your ND filters and the pre-ND exposure. Before attaching the filters, measure the exposure using a spot meter or your camera’s internal meter (press the shutter half way down). I often take a couple of “regular” exposures at this time and evaluate my histogram to confirm that the exposure is correct before attaching the ND filters. Note the shutter speed. Remember that a stop of light is the doubling or halving of the total amount of light that hits the sensor. A three-stop ND filter, for example, extends your shutter speed by three full stops. So, if your original metering gave you a shutter speed of 1/125s, with a three-stop filter you would increase that to 1/15s (1/125s to 1/60s is one stop, 1/60s to 1/30s is two stops, and 1/30s to 1/15s is three stops). However, to really slow the exposure you will want around 16 stops of light reduction. With a 16-stop filter, the mathematics can get a bit tedious. Use a chart or better still a phone app to help you convert. On a chart in the ‘No Filter’ row, find your metered shutter speed. From here, drop down to the row describing the ND filter strength you are using. Where this row and column intersect is your new converted shutter speed. Alternatively, download an exposure calculator onto your phone and follow its instructions. With a 16-stops filter (a 6-stop and 10-stop stacked together), that 1/125s initial exposure turns into 8 minutes!

Taking the Shot

With your filtered shutter speed calculated, switch the camera to manual mode. Set the aperture you chose in section 5.2. Set your shutter speed to bulb. Making sure that your focus is correct, and that your tripod head is securely locked down, carefully attach your ND filter or set your adjustable filter. To prevent any light from leaking into the camera, cover your camera and lens with a dark cloth or jacket and secure it with clips, especially if it is windy. During very long exposures, light has a way of sneaking into your camera, particularly through the viewfinder. You are now ready to take the picture. Using a cable release, press and lock the shutter open. Set a timer on your watch or phone, sit back, relax, and plug in your music while you wait.  When your timer goes off, unlock the cable release to stop the exposure. Don’t worry if your exposure is not exact. With exposures of several minutes, leaving the shutter open a few extra seconds will not affect your overall exposure.

6. Some Tips

Check your histogram. I often find my images need a longer exposure than what I initially calculated. If your histogram is bunched up on the left, increase your exposure time by a stop. That means doubling the length of the exposure. If you took an eight-minute exposure, try 16 minutes. I usually shoot three shots of each image and bracket each one by ½ or a full stop, depending on the dynamic range of the composition. In Photoshop you can merge the images using layers and layer masks. Make sure you are shooting in raw. This will give you the most latitude when you are processing your images. Turn off the noise reduction in your camera. With these long exposures, your sensor will heat up, and you will see a lot of noise in your images. However, using the in-camera noise reduction tends to cause a loss of detail. I prefer to deal with noise in post processing so I have complete control over how much and how it is applied. In addition, using noise reduction doubles your exposure time. Noise reduction takes a second photo immediately after the first, only this time the shutter remains closed. This ‘dark frame’ is used to electronically subtract the noise from the initial photograph. I enjoy the slower pace of long exposure photography, but not enough to double the length of each exposure! Let your sensor cool off a few minutes between exposures. This will help to mitigate some of the noise that builds up when the sensor gets hot. Make sure you have a fully charged battery and a couple of spare ones in your bag. Long exposures, especially in colder weather, consume batteries very quickly.

7. Final Thoughts

Creating images using very long exposures are a refreshing change from shooting “regular” photographs. They force you to think very carefully about your composition. A single shot can take upwards of 45 minutes to an hour from conception to completion, including bracketing. It reminds me of the film days before digital when every shot was carefully thought out and calculated. You could not afford to shoot hundreds of images hoping for one keeper. As an afterthought, if you are taking long exposures of the sea to get the cotton candy effect of waves be very careful to check the tides after all in 45 minutes to 1-hour exposure and composition times the tide can come in and at best interrupt the shot but at worst take your camera and gear away on a wave or even cut you off from land, think about your location carefully.

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