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Tuesday
Jul172012

How-To: Shoot Long Exposures

Long-exposure photography can turn night into day, stillness into motion, and the mundane into the beautifully abstract. It's one of many techniques in a photographer's collection that can help to transform what the naked eye sees, and what the mind's eye envisions, into a photograph. As with any technique, there are numerous variations and small nuances to be learned. However, there are a few guidelines that can help get you started along the way to becoming proficient. Remember: this is not by any means a complete set of guidelines that will work for everyone's equipment and shooting style. Take what you learn here into the field and expand upon it by learning from your own experiences.

Cidade Maravilhosa (Rio de Janeiro)
Six Seconds on a Thursday in June

Equipment

This may seem obvious, but the first thing that you'll need is a camera with a manual mode, to allow for fully manual control of shutter speed, aperture, and ISO. A digital SLR camera is best, but you can also do long exposures with a point & shoot as long as it has an "M" mode.

The second thing that you'll need is a stable tripod. Unless you're doing some seriously abstract work, the camera needs to remain perfectly still while the sensor gathers light during your long exposure. Even the smallest jostle or vibration during exposure can mean significant blurring in the resulting image. If you're serious about photography, I recommend spending at least a few-hundred dollars on a solid set of tripod legs, and another few-hundred dollars on an excellent ball head. This may seem like a lot of money, but a high-quality tripod and ball head will last you a very long time if you take care of them. These things don't go obsolete every few years like most digital camera bodies. Do your research carefully as there are many different features to consider when looking at tripods. Roger Cicala, owner of LensRentals.com, has a very comprehensive article about tripod selection here: Lensrentals.com: Choosing a Tripod.

Besides your regular extras like spare batteries and memory cards, the third thing that you'll need is a remote. This is somewhat optional, since you can get by with the camera's self-timer, but most cameras limit exposures to 30-seconds this way. If you want to take photos with truly long exposures (like star trails) or in very dark environments (like the deep woods at night), you'll need a remote. Many remotes offer all sorts of convenient features like backlit timers, wireless connectivity, and interval timing for time-lapse photography. The other important thing about using a remote is that you won't jostle the camera while pressing the shutter button.

Procedure

Once you get on location, carefully setup your tripod and the rest of your equipment. Unless you absolutely must have the tripod's center column extended to achieve a certain composition, leave it down. Leaving the center column un-extended will help minimize vibration and camera movement. Another trick that can help to stabilize the tripod is to hang your equipment bag from a hook on the bottom of the tripod's center column. If you're shooting from a soft surface like sand, snow, or mud, then make sure the tripod legs are properly entrenched in the surface so they don't sink or move during the exposure.

Once your tripod is set up, go ahead and mount your camera to it. I won't go into detail about composition here since that's a topic that has already filled volumes, but take your time and carefully envision the resulting image; think about your framing. You may need to reposition your tripod if you're not quite happy with initial composition.

Put your camera into manual mode (M). This will allow you to control shutter speed and aperture manually, instead of letting the camera control it for you. Turn auto-ISO off, and set it to the base value, which is usually 100 or 200. If you have an optically stabilized lens (often called IS, VR, OS, or VC), or if your camera has in-body stabilization, turn it off. Stabilization is fine for shutter speeds around 1/2 second or shorter, but during long exposures the camera remains perfectly stable, and slight movements in lens elements or the camera sensor can cause a reduction in sharpness. Unless you're trying to create a specific creative effect, leave the camera flash off.

White balance can be an important consideration, since it's difficult to correct and change in JPEGs. If you are shooting RAW files, then it's less important to get this setting spot-on in the camera. I highly recommend shooting RAW, but if you'd like to do more reading on the differences between JPEG and RAW, here are two informative articles to get you started: [1] [2].

Since we're doing long exposures, the sensor can heat up and generate some pixel noise, even at base ISOs. Most modern cameras will have a long exposure noise reduction mode. When enabled, it will trigger a second exposure of equal length to your initial long exposure, except this one will be taken with the shutter closed. This "black" frame contains the image sensor noise pattern which will then be subtracted from your actual long exposure image, reducing its noise characteristics. The only downside of using this mode is that exposures take twice as long: a 30-second exposure takes a total of 1-minute because of the second 30-second dark frame exposure. This isn't so bad for shorter exposures, but can be frustrating during exposures that last many minutes (like star trails). Despite this, I highly recommend enabling it for better image quality.

If your camera has live-view mode, use it to focus, since it's the most accurate method. If you don't have live-view mode then use the most-accurate center focus sensor. If it's completely dark outside, and you're not able to autofocus on your subject, I recommend trying to focus on something far away like the moon, and then switching to manual focus and dialing it back just a hair. If you're going to focus the lens manually, be very careful not to turn the focus ring until it reaches the hard-stop. For most most modern lenses the hard-stop is a focus point that's slightly beyond infinity, and focusing there reduces sharpness considerably. If you're an advanced user, it's important to consider hyperfocal distance while focusing. If you're more casual, then it's usually just fine to focus right on your subject.

Get out your remote remote trigger/shutter, plug it in, and make sure that your camera is in "bulb" mode, which means that the shutter will be open as long as the remote is triggering it. If you don't have a remote, or don't want to use it, then set your shutter speed in-camera (up to 30-seconds on most cameras), and use the 2-second self-timer. If your camera has mirror lockup mode (MUP or MLU), enable it. This is yet another trick to reduce vibration. Mirror lockup mode will force you to trigger the shutter twice: once to flip up the mirror, and again to open the shutter. Wait a few seconds between flipping up the mirror and triggering the shutter, since mirror slap can cause small vibrations that reduce sharpness. If you don't have a remote, then mirror lockup mode isn't helpful, since you have to touch the camera body in order to trigger the shutter. In this case, I'd recommend just going with the self-timer. Some cameras even have an exposure delay mode, which waits one or two seconds between flipping up the mirror and triggering the shutter.

Finally, it's time to set the exposure on your camera. Since most lenses are sharpest 1 or 2 stops down from their maximum aperture, use that as a guideline. Most modern-day long-exposure and landscape photographers shoot somewhere between f/4 and f/8. You can go past f/8, to f/11, f/16, and beyond, but be aware that diffraction will start to rear its ugly head. At apertures beyond f/8, you'll really begin to notice a loss of sharpness with each stop down. I only recommend going beyond apertures of f/8 if it's absolutely critical to achieve greater depth-of-field or longer exposure times.

Now you can go ahead and snap away! Use the camera's light meter and tune your exposure using shutter speed and ISO. After taking your first image, use the histogram to verify that the exposure looks correct. Don't rely on the LCD screen brightness, since it can be misleading in dark areas. If your exposures are going to be far too long to double-check, then first shorten them with higher ISOs, and then adjust the shutter speed and exposure together in 1-stop increments. For example, an exposure of 2-seconds at ISO 6400 is equivalent to an exposure of 4-seconds at ISO 3200, and so on, until you get 2-minutes at ISO 100.

Shooting Checklist

This checklist is a summary of the above, and is meant to serve as a very broad starting point for you. Take it and modify it so that it works for your equipment and shooting style.

  1. Set up tripod, leaving center column un-extended if possible.
  2. Camera to manual exposure mode (M).
  3. ISO: base value (usually 100 or 200), and Auto-ISO OFF.
  4. Aperture: between f/4 and f/8 for best sharpness (on full-frame or APS-C sensors). Use diffraction-prone apertures of f/11 and higher only if necessary for greater depth-of-field or very long shutter speeds.
  5. Flash: OFF (unless you're trying to achieve a stop-motion effect).
  6. White balance: as desired (JPEG shooters should pay more attention, RAW shooters can adjust more easily during post processing).
  7. Lens image stabilization or vibration reduction (VR / IS / OS / VC): OFF.
  8. If you have a remote, use it and set your camera to bulb mode! If you don't have a remote, use the 2-second self-timer.
  9. Enable mirror lockup mode (MUP / MLU) or exposure delay mode if you have it.
  10. Enable long exposure noise reduction mode if you have it.
  11. Autofocus on your subject with live-view, then switch to manual focus and adjust for desired hyperfocal results (don't forget to refocus if you change your lens focal length). Do NOT focus beyond infinity, since this will reduce sharpness.
  12. Stabilize your tripod by hanging your camera bag from it, and shield the tripod setup from any heavy winds with your body.
  13. Take some test exposures observing details in the photo for sharpness and the histogram for desired exposure (as opposed to the LCD screen brightness).
  14. Adjust exposure with shutter speed and ISO.
  15. Adjust depth-of-field with focus adjustment and aperture adjustment.

After you're done, don't forget to change your settings back to the usual that you shoot with (Auto-ISO enabled? VR on, self-timer off, MUP off).

I hope you've enjoyed this short tutorial. Good luck out there!

Underground Rail