A Guide to Long Exposure Photography

Many of the images in my portfolio are shot at the start and end of the day using a long exposure. In this post I'll give some pointers to get you started with long exposure photography.

I love long exposure for several reasons. One is that it captures something that isn't always obvious to the eye. The passage of time can render skies, water and likes as pleasing streaks that otherwise we just don't sense.

The other major reason is that I feel it has a simplifying effect on a composition. Individual clouds, or bubbles and splashes In water can add to the visual clutter of a scene, confusing the eye about what's important in the scene. It can help to create more abstract, strongly graphical images.

You might think “what's to know? Set a long shutter speed, job done". Well ye, that will give you a long exposure! However there are several factors and techniques to consider if you want to increase your success rate.

How to Get a Longer Exposure

Normally I consider a long exposure to be 1 second or longer, possibly 30 seconds or even minutes long. With certain subjects such as fast flowing water you can achieve a good long exposure (LE) effect with 0.5 seconds or perhaps less. But normally upwards of 1 second is the goal.

If you're aware of 'Sunny 16' rule then you'll know that to on a sunny day an exposure of 1/100 @ f16 ISO100 will give you a good exposure. Given that ISO100 is as low as our camera will go and f16 is approaching the limit of our aperture options then it's clear we've got some work to do to get our shutter speed from 1/100 to 1" or more, which is about an 8 stop difference!

The solution is to reduce the light entering the camera. There are several ways to do this:

1. Overcast conditions: a sunny day will play havoc not only with shutter speed but also by introducing high contrast unpleasantness to the image. An overcast day gives us  lower light intensity and also gives us much softer light to work in, sometimes making the landscape 'glow'. The difference between shooting e.g. waterfalls in sun and overcast conditions is immense!
2. Shooting early/late: an obvious way to cut out light is to shoot when the light is fading. This will naturally give you much longer exposures.
3. Narrow aperture and lowest ISO: normally for LE you'll probably be using an aperture of f16 or f22 and an ISO of 100.
4. Neutral density filters: these are like sunglasses for your camera. Most come in 2 or 3 stop varieties but you can get higher, including the now infamous Lee 'Big Stopper' which is 10 stops! These can be useful if there's still too much ambient light. Depending on your filter system you may be able to stack 2 or more to multiply their effect. This may allow you to shoot in sunlight but given the contrast issues you still face generally I'd advise against it.

Tools

For best results, you'll want to use the following.

1. Tripod: We're working with fairly long shutter speeds so we really need to use a tripod. See this post for pointers on tripod usage. We also want to partner the tripod with a remote release to minimise camera movement. 2. LiveView: I'll post another time about how I use LiveView for most of my shots but for now it's enough to say it’s really useful for LE work. Trying to compose with filters in dark or murky conditions can be really difficult through the viewfinder. Using an exposure simulation mode in LV gives us a much bigger and brighter display to work and compose with. Further LiveView acts like mirror lock up so you don't have to separately enable MLU to reduce camera movement. 3. Live Histogram: The live histogram in LV can also be really useful. There's nothing more frustrating than waiting 30 seconds for the exposure to finish only to find you've clipped all the highlights. Live histogram lets you spot potential issues before tripping the shutter. 4. Long Exposure Noise Reduction: if your camera has it, it's well worth switching on. Certainly I've "ruined" several minute-long shots by not having it on, they are just a bit of a noisy mess. The way it works is to take two identical exposures – the actual image and another with the shutter closed (a dark frame). The noise that appears in the dark frame is then subtracted from the original exposure. What this means is that each exposure takes twice as long as it should which can be annoying, but it's worth it. There are tricks you can use to shoot a single dark frame manually and then apply the noise reduction to each image in postprocessing, but I won't cover that here. 5. Bulb mode: for some reason (making money being the most likely main one!) our cameras can only make a 30 second exposure themselves. For a longer exposure we need to use Bulb mode, where the shutter stays open for as long as we decide. I’ll cover some techniques to consider in Bulb mode below. 6. Neutral Density filters: as mentioned above, an ND filter will help you get longer shutter speeds if you can't get one using other ways first. Note you mostly need a full ND filter (which is just one piece of dark glass) rather than an ND Grad which has a clear to dark transition (to balance sky and ground). That might be useful as well, but we want to use a full ND to make the whole image darker. 7. Head torch: quite often you'll be going to or from location in the dark, especially if you lose track of time and shoot deep into twilight. A head torch for safety is really important. It also helps you rummage around your bag in the dark, and can illuminate objects in the scene to help compose when it's really dark. You could even do a spot of light painting!

Subjects

If you're interested in long exposure then you probably know what makes a good subject already. The typical ones are water and sky. Water takes on that soft, silky effect that we've all seen in waterfall pictures. Skies render as lines across the sky as clouds go scudding by carried by the wind.

There are other subjects though and it's probably better to consider the result you're looking for to determine if LE is suitable, rather than looking for LE subjects. Other obvious examples are:

• light trails, where e.g. car lights become long, bright streaks in the image
• people moving which can create "ghosts" moving about the static landscape.
• trees and grass, showing them swaying in the wind. Note it can be difficult to make this look desirable rather than an accident! Make sure that they are a key element in your composition.

Composition

One of the bad habits I see with a lot of long exposure images is that it's almost as if the LE is the subject. Almost like 'bad HDR' the LE is used to create a 'wow' factor to distract the viewer from the rest of the image.

The best advice I'd give is to compose the shot as if you weren't using LE, to create an image that has merit in the first place. I will often crank up the ISO, widen the aperture and remove my filters to give me a more normal shutter speed whilst I am working the scene towards my final composition. Once I'm happy I'll start taking my LE shots.

So follow the usual 'rules' of composition - consider strong foreground, look for leading lines and curves, simplify by reducing visual clutter, and so forth.

You will need to learn to anticipate the effect of the LE on objects. This will come with time. As a couple of examples you can start by considering the direction and speed of the clouds and water, and by looking for patterns created by foam in the water which will render as white streaks.

When shooting skies at night, be aware that stars and moon will blur and streak approaching 30 seconds at 24mm. Either make use of the effect (star trails) or avoid it.

Focusing

Your autofocus probably isn't going to help much with long exposures as it will be too dark for it to obtain focus. So you will have to focus manually. There are several ways you can do this.

If you're using LiveView as a I suggested above then it usually gives you a bright enough image that you can manually set and check focus.

If you have a distance scale on your lens and have a depth of field calculator, then setting your lens to the hyperfocal distance to maximise your depth of field is a good move.

Make sure to either switch your lens to manual focus or to move the focus function to a button other than your shutter button. Otherwise the camera will try to refocus when you take a shot.

Shorter Long Exposures

If you’re using a shortish LE shutter speed, say in the 1-10 second range, then it helps to add a sense of movement to the image without making it too abstract. At these speeds when you trip the shutter will be important. If you’re at the beach for example, then generally the best time to shoot is when a wave has just come in. The receding wave will leave white foam trails around rocks.

A classic long exposure shot is of waterfalls. The usual look is one of silky smooth water which can be achieved with an exposure of a second or two. Generally the longer the exposure the more silky smooth it gets, but beyond a few seconds it's a case of diminishing returns. It's often not neccesary to shoot for longer than 10 seconds.

If you’re unfamiliar with long exposures and want to develop some basic experience then I would suggest sticking to shorter exposure lengths, 10 seconds and less. It can be incredibly frustrating shooting longer exposures (noting that noise reduction doubles the exposures again) when you’re not seeing the results you’re after. Once you get a feel for the effects of LE then it will be much easier to shoot longer exposures.

Really Long Exposures

At longer shutter speeds, 20 seconds and more I’ve found that things become increasingly abstract. If you think about how light renders on the sensor, as things move over a longer period it has the effect of “averaging out” the motion across the sensor.

That is on a short exposure, the movement will only cover a small portion of the sensor. On a longer exposure, the ongoing movement will have registered on more of the sensor. As an example, a darkish sea with white waves coming in would have distinct dark areas with white lines and streaks with a shorter exposure. With a longer exposure, the waves will have registered as larger patches of white and grey, the individual movements becoming less

distinct and the shape more uniform and more abstract. Because of this, timing of the shutter is less crucial. Over 30 seconds many waves will have contributed to the image, so the exact timing of the first wave doesn’t really matter.

You will also see that with longer exposures you can get a sort of “misty foam” that appears around the base of rocks. Again this is from the “averaging” effect of the long exposure. For some of the exposure, a wave was lapping at the rock. For the rest of the time the rock was untouched by the water. The “average” of these two is that the rock is visible with the faint impression of the water movement around it.

You can also use long exposures to “obliterate” distracting objects. Not literally of course! A rock that has waves coming over it during the exposure will start to merge with the sea around it in a LE, rather than being a distinct object. I’ve used this trick several times to remove clutter. Watch the waves for a while and if they are coming over a distracting object, you can use this to reduce their presence in a LE image.

Reacting to Changing Light

If you’re shooting at the extremes of the day, remember that the light is probably changing really quickly. It doesn’t change so quickly over a shorter LE, but what your camera metered for 2 minutes ago likely won’t be what it meters now. So you have to anticipate how the changing light will impact your image. You could get technical with it and use a lightmeter to measure the changing light. Personally I use intuition.

Before sunrise, during twilight proper, the light is changing but relatively slowly. You’ll then become aware of it getting brighter quicker as the sun approaches the horizon. If you don’t notice this visually (your eyes adapt very quickly) you will start to see your shutter speeds coming down. If I’m shooting into the minutes I will probably knock ½ or 1 stop off the shutter speed to compensate for the brightening conditions. So if I was metering for 4 minutes, I would shoot for 3 or even 2 instead.

At the opposite end of the day, obviously things are going in the other direction. So if I’m metering 4 minutes I would increase that to 6 or 8 minutes. As you can see, as it gets darker your exposure times double and can become unreasonably large (especially with long exposure noise reduction) so I would probably start to widen my aperture and/or increase my ISO to maintain a shorter shutter speed. So if I was metering at 4 minutes I would bring that down to 2 minutes by changing from f16 to f11, but I would actually shoot for 3 minutes to compensate for the darkening conditions.

It’s very difficult to explain this approach in writing! I think that’s because it’s something you have to experience and understand before you’re able to react in the right way. There’s no way of predicting the point where the light starts changing quickly, so you just have to be aware of and observe it.

More About Bulb Mode

As I said at the top for exposures longer than 30 seconds you need to use Bulb mode. This means a few things.

Firstly, we definitely need a remote release – you don’t want to stand with your finger on the shutter button for a minute!

Secondly, we need to become better familiar with the aperture-shutter-ISO triangle. If you’re metering 20 seconds at f11 and change to f16, the camera won’t work out the new shutter speed for you – if you’re in aperture priority (Av) you will just get a blinking 30” telling you it’s out of range.

You need to know yourself that going from f11 to f16 means you need to double your shutter speed to 40”, and then you’ll need to time that yourself in Bulb mode. On my camera, a Canon 5D Mark 2, the top LCD display provides a handy clock showing the exposure length. The downside to this is that you have to be able to see it – often the camera is too high or it’s too dark. I bought a remote release with a timer on it to help me but a stop watch (either on your wrist or on your phone) would work perfectly well.

For very long exposures you might be wondering how you decide on the shutter length. If the camera is blinking 30” at you, then how do you decide how long? The answer is to do the opposite of what I say above. I widen my aperture until the 30” is no longer blinking to know how many stops extra shutter speed I need.

This is probably best illustrated with an example.

If I’m getting a “blinking 30” at say f16, I will widen my aperture one click at a time, f11 (1 stop), f8 (2 stops), f5.6 (3 stops) until the shutter speed is no longer blinking at me (this could be 30” or maybe 25” or 20”) . I now know that my shutter speed needs to be 30” x 2 x 2 x 2 = 4 minutes to add the 3 stops of extra light, and I set my aperture back to f16.

This isn’t bulletproof. When it’s very dark your camera’s meter starts to struggle. If you’ve got a filter on you can remove it to improve the meter accuracy before putting it back on for the actual photograph (remember to add the extra stops from your filter to the above calculation!). Also remember that your meter is expecting a neutral grey scene – if your scene is dark or bright relative to neutral grey then remember to compensate for that.

Again, experience and intuition help you to adapt.

Conclusions

As you may have gathered I favour shooting with longer exposures, 20 second and up. I just love the effect, particularly on water. But experiment with a variety of shutter speeds to find what’s pleasing to your eye, and importantly what best matches the subject. For example, if you want to convey a rough sea, a very long exposure will average out and give you what looks like a very flat sea! A shorter exposure that’s short enough to make waves distinct but long enough to register some movement in the waves would probably be more appropriate.

The above hopefully makes you realise that there is no real "trick" to LE. There are some things to get right, and there's some experience required to anticipate the effects of movement and light. As with anything (good, mindful) practice makes perfect.

As I say above, I think the most important thing is to start with a good image and then apply long exposure to it. Using long exposure as a crutch to make a bad image “good” is doomed to gimmicky failure.

Please do let me know in the comments if this is helpful or if something doesn’t make sense!