TRY TIME EXPOSURES FOR ETHEREAL EFFECTS

When we think about taking long exposures with a camera, night time images usually come to mind. Only dark conditions generally call for slow shutter speeds, right?

True-but there is a way to take time exposures in broad daylight...with surprising results.

So the first question that comes to mind is: how do you take a long exposure in bright light? Won’t the camera try to set a fast shutter speed to ensure that the exposure is correct, regardless of how small the aperture is set?

Then there’s the other question: why would you want to take long exposures in daytime, anyway?

OK - a long time exposure (keeping the camera’s shutter open for a long time – from seconds to minutes) will occur when:

• Light level is very low
• A very small aperture is chosen, and
• ISO is set to the lowest value that the camera will allow.

So, to answer the first question, you need to simulate low light conditions by giving your camera dark sunglasses. The device that will do this is an inexpensive thread-on piece of glass called a neutral density (ND) filter. These filters come in a wide variety of grades and are either specified in ‘stops’ or ‘times’.  They are also available as variable grade versions, often referred to as Fader NDs. Be sure to buy one that has the same filter thread diameter as your lens.

A one-stop (or two times) ND filter, with aperture and ISO remaining the same, will require that you force the shutter to stay open twice as long to get the same exposure as you would without the filter. Similarly, a two-stop filter will require slowing the shutter by four times, since a stop means a factor of two in exposure. For the kind of images I’m proposing we take, you will need a ten-stop filter in order to get exposures that are minutes long. This is equivalent to increasing exposure by a factor of 1024 times, but is usually referred to as a 1000 times filter.

Why minutes? Well, in answer to the second question above, anything moving (water, clouds) will take on a foggy (in the case of waves) or streaky (in the case of clouds) look. As long as you have stationary elements in the scene, such as rocks, ground and a tree trunk in the sample shots shown in this post, the viewer is confronted with a paradox that doesn’t appear ‘natural’. This makes for a more interesting image than if you had captured the same scene with a shutter speed of, say, 1/250^th of a second. While these images were shot in colour, I converted them to black and white, since they tend to look more dramatic that way.

And now for the practical considerations. You will need:

• A stable tripod
• A remote shutter release that plugs into your camera, since you can’t hold down the shutter button on your camera for minutes without jarring it. You can also get an intervalometer, which allows you to set a specific time interval without having to manually time the shutter.
• A camera with a Manual mode that will allow you to set the shutter to ‘Bulb’, or one that has a dedicated Bulb mode.
• A day with calm winds, so that your tripod doesn’t get buffeted during the exposure.

Look for a scene that has a combination of moving and stationary components. Getting the right exposure is definitely going to take some experimentation. As a starting point, set your camera’s ISO to the lowest value it provides. This is typically 100. Do NOT use Auto ISO. In Manual / Bulb mode, set the aperture to a value anywhere in the range of f/16 to f/22. This will depend on whether it’s an overcast or sunny day. You should get exposures in the range of 2 to 4 minutes. Use the histogram to confirm good exposure and tweak the time (or aperture) as needed to get perfect exposure or desired motion effect.

With digital SLRs, a practical consideration is the heating of the sensor during long exposures. While it won’t damage the camera, this heating tends to amplify what are often referred to as ‘stuck pixels’. Every camera has them, and they appear as unexpected bright spots on the final image.

To combat this, DSLRs generally have a long exposure noise reduction setting which can mitigate this annoyance. Unfortunately, it requires that the camera will make you wait twice as long to see your image, since it takes as long again as the exposure time to process out the stuck pixels. This could result in an 8 minute wait until you take the next shot. While this technique is effective, I prefer to take my chances and fix the spots after in either Lightroom or Photoshop.

By way of a summary, here are the steps I take:

1. Set up the camera on the tripod and compose the scene with the chosen lens.
2. Ensure ISO is at its lowest setting, and choose a small aperture to help force a long exposure and to give me the depth of field I want.
3. Plug in the remote shutter release or intervalometer (and set it to the exposure time I want).
4. Thread on the ten-stop ND filter, being careful not to disturb focal length or focus settings.
5. Cover up the eyepiece if the sun is behind me, to prevent light leak onto the image (it has happened to me!)
6. Check my image and histogram, rinse and repeat until I get the right exposure and effect.

It’s a slow process that requires patience. At the end of it though, you will get images that will be set apart from the ordinary.

MAGIC HOUR

Here’s the typical professional travel/landscape/fashion photographer’s day:

1. Get up well before dawn and drive to a location scouted the day before.
2. Shoot as the sun comes up.
3. Go back to the hotel by about 8 or 9 am for breakfast.
4. Do some personal tours in town.
5. Have a late lunch.
6. Go back to the hotel for a long siesta.
7. Start out late afternoon and scout locations for tomorrow.
8. Find a place to have dinner.
9. Get to next location for the evening’s shoot well before sunset.
10. Go to bed early, rinse and repeat.

Huh? What happened to partying until dawn? There’s always the afternoon for taking pictures, isn’t there?

Well, no. The reason that pros avoid mid-day sun is that it provides the coldest light and the worst shadows imaginable. With the sun directly overhead, the colour temperature is at its highest (counter-intuitively, perhaps), resulting in a very bluish light. As a result, colours look washed out and take on a cold cast.

Alternatively, shooting in the magic hour around dawn or dusk provides a warm (low colour temperature) orange-red light that increases colour saturation and contrast. The reason is that when the sun is low in the sky, it is filtered through more of the earth’s atmosphere because of the low ‘grazing’ angle. Shadows are also longer, resulting in more drama. Particularly at the evening magic hour, a clear sky also takes on a deep inky blue hue when you shoot facing away from the sunset. Is there any wonder that commercials, particularly for automobiles, are shot around magic hour?

 Now, sometimes logistics dictates that a shoot has to be done in the middle of the day. Cinematographers often get around this by using warming filters and light modifiers. These modifiers may be elaborate tents to diffuse the harsh overhead sun and eliminate hard shadows, or they may be coloured reflectors aimed at the subject to modify the apparent colour temperature. If you’re faced with this situation and you need to get the shot before the bus leaves for the next tourist trap, consider taking filters (polarizing, warming and graduated, for example) and maybe a photographer’s umbrella or reflector to help mitigate the lousy light.

 Best advice: consider a car rental to allow you to scout freely and return to a location when the light is at its best. And, you’ll get to discover more about your host country as you take the back roads to your next shoot.

 

Have a look at these shots, taken during Magic Hour, and see if you can spot why it's the best time for photography.

 

Meter this.

We’ve all seen the portrait photographer holding a white-domed object next to the subject’s face to take a light reading. So why is that being done? Why not just let the camera do its automatic exposure thing and take the picture?



 

It’s a good question in this digital age, where we can instantly review our shots to see if we need to re-shoot with a little exposure compensation. After all, the histogram in the camera tells us just about everything we need to know about the exposure in the shot – is it under- or over-exposed and is the exposure evenly distributed over the entire tonal range?

The short answer is that the handheld meter is mostly used to measure the light falling on the subject from studio strobes or flashes mounted off-camera.  In this scenario, the camera doesn’t typically have the ability to control the flash output, as it does in ETTL mode when the flash is mounted on the camera’s hot shoe.  Hence, studio photographers usually work with the camera in manual exposure mode, where they manually set the shutter speed to a value that will synchronize with the flash and the aperture to a value that gives the correct exposure. Alternatively, they can use the  meter reading to set the brightness of each flash in a multi-light setup to give a particular effect while ensuring a proper exposure.

Here, I’ve used the words ‘light falling on the subject’, meaning incident light. Hence, the incident light handheld meter measures the ambient light and ignores how much light the subject is likely to reflect.  The metering system in our camera, on the other hand, does rely on the light reflected from the subject to determine exposure.

Which is more accurate? The incident meter is, because it is calibrated so that it will give camera settings to make an 18% grey card look like 18% grey (middle mark on the histogram) when photographed.  The reflected meter, however, relies on the subject's tone averaging out to 18% grey in order for the exposure to be accurate. If the subject is overly dark or bright (such as a snow scene), the reflected meter gets fooled because it tells the camera to expose as if the subject is mid-grey. The incident meter would read the light falling on the snow rather than the light reflected from it, thereby resulting in the snow looking like bright white snow rather than grey slush.

I started out stating that the incident meter is used in the studio to measure the light from strobes or flashes, but obviously it has a function in outdoor ambient (continuous) light photography as well. Some photographers work in manual exposure mode all the time and therefore rely on an incident meter for camera settings.

So why bother? Part of the answer may be a throwback to the film days, where you never knew until it was developed whether you got the exposure right or not. An incident meter (and a little exposure  bracketing) gave you the confidence that you got the shot. That way of working may still influence the photographer who has made the transition to digital, partly because it’s good practice.

The bottom line, though, is that anyone seriously considering turning pro using studio lighting setups should consider working with a combination flash/continuous incident meter, if for no other reason than to save time. The alternative is to shoot, tweak, shoot and then tweak some more.

Combination meters can be a bit of an investment, so they’re not for everyone.  If you’ve got the spare change, though, a meter can help you understand the exposure mystery a little better and hit the bullseye every time.

Fill Flash: Balancing Ambient Background and Subject

I've often ranted in my courses about how horrible mid-day light is for photography. Apart from the colour temperature concerns - an overly bluish, cold tinge to the light - harsh shadows cast from overhead are unflattering, particularly on human subjects.

The flash, either the built-in pop-up variety or the accessory hot shoe type, can assist if you are forced to shoot in the daytime outdoors. Weddings fit this scenario. Turning on your flash to shoot outdoors may seem absurd, but pros use it all the time as 'fill flash'. The word fill refers to the fact that the flash illuminates the face to fill in shadows in the eye sockets and under the nose and chin. Photographic Botox®, as it were.

The modern digital SLR does its best to balance the ambient outdoor light and the fill flash through ETTL (evaluative through-the-lens) metering. ETTL uses a number of different points on the image to determine what the correct exposure setting (ie. aperture and shutter speed) should be, and controls the output from the flash to properly illuminate the subject.

As brilliant as the microcomputer in the camera is at doing this, results can sometimes be other than expected. Let's say the background looks properly exposed but the subject looks a little dark. If you have a strong backlight, this may mean re-positioning your subject. If that's not possible, you can adjust the flash output, independently from the camera's exposure setting, by using flash exposure compensation.

Accessory Flash Exposure Compensation

There are two ways you can change flash output. The accessory hot shoe flash will allow you to adjust output using either the buttons on the flash itself OR through the flash exposure compensation setting in the camera. Depending on the camera, either the camera's flash exposure compensation will be used or the setting dialled into the accessory flash will be used: they cannot be used in combination. For the built-in pop-up flash, you can (obviously) only use the camera's flash exposure compensation setting. So, for the underexposed subject, set the compensation for, say, +2/3 stop and try again. The subject should brighten and balance with the background. 

Exposure Compensation button on camera

For the opposite scenario - the subject is properly lit by the flash but the background is too dark, you can use exposure compensation to control the background exposure. This is different from flash exposure compensation in that it controls the choice of aperture and/or shutter speed but not flash output. For a dark background, dial in a positive number, and for an overly bright background, dial in a negative number. You may have to tweak the flash exposure combination again to get the best result.



Negative Exposure Compensation plus
positive Flash Exposure Compensation

So, by setting flash exposure compensation and exposure compensation independently, you can achieve a balanced image.

Let's leave the mid-day scenario and think about doing a portrait just after sunset ('magic hour'). Using aperture priority or shutter priority modes, the camera's metering system will try to expose the twilight sky properly before lighting your subject with the flash. If the subject looks overly bright and unnatural against the sky, you can balance them by using negative flash exposure compensation or a bit of positive exposure compensation, or both.

The results from doing so will amaze you. After all, the pros adjust their light sources to balance them against the ambient light.

Guide Numbers and Watt-Seconds

Whenever I think about hauling lighting equipment to a location, the question comes up: Should I take a.c. strobes, extension cords and power bars, or will a couple of hot-shoe flashes, umbrellas and stands do it? Hmmmm...I know what I'd prefer.

The trouble is, hot-shoe flash output is (usually) expressed in Guide Numbers (GN) while strobes are rated in Watt-seconds. Sadly, there is no easy way to relate the two, so I made a quick setup to measure the output of each. I've always assumed that a 150 Watt-second strobe would blow away a flash in terms of light output, but I was about to be surprised.

Now, we should start with definitions. GN is the product of the distance of the flash to the subject and the f stop being used at a particular ISO setting (or film speed). Example: I set my flash meter at a sensitivity of 100 ISO and placed it at 10 feet from the flash. I fired the flash and read the f stop it was recommending. For a flash rated at GN 80 (ft - ISO 100), you would read f/8 on the meter (f/8 x 10 ft). Indeed, my Sigma EF 500 came in close at f/7.6 (hence a GN of 76).

Next, I set up the 150 Watt-second strobe at the same location as the flash, set it for full power, and blasted away. Here's the surprise: it read f/7.9 on the light meter, meaning its GN equivalent is 79, which is barely better than the Sigma. Admittedly, there are a couple of variables here. One is that the light meter is older and uncalibrated, and the Sigma's batteries may not have been at peak voltage. The point, however, is that on a relative basis you can determine how your strobe/flash sources compare. This is particularly helpful when the manufacturer of the flash doesn't provide the GN.

So GN is a measure of the amount of light available for proper exposure of a subject at a particular combination of distance from the flash and camera aperture setting, on a camera set at a particular ISO sensitivity. On the other hand, Watt-seconds are a measure of the electrical energy expended in the strobe tube (Watts are the rate at which energy is used, so multiplying by time gives energy used over that time period). This measure doesn't take into account the conversion efficiency of the tube from electrical energy to light energy, or the effect of the reflector behind it. Hence, GN and Watt-seconds can't be related mathematically.

Bottom line: measure the output of each with a flash meter so you know how they relate. Similarly, if you double the Watt-seconds you can expect the guide number to double, since it should add another stop to the flash meter reading.

Then, you write your results down, as I did, so that confusion doesn't ensue.