How Do I Access Stroboscopic Flash?

Many of today’s high-end Speedlights such as the Canon 580EX/EX II and Nikon SB-800/900 have this feature built in. Canon refers to this feature as Multi Mode while Nikon calls it Repeating Flash (RPT). We’ll be using a Nikon SB-800 for this tutorial, but all of these concepts can be applied to any flash with a stroboscopic mode.

Stroboscopic flash is first controlled by the flash output, frequency, and number of frames. First, you set the power level of your flash just as you would in manual mode. Frequency, expressed in Hz, represents the number of flashes per second. The number of flashes represents exactly how many times your flash will fire at a given frequency. Keep in mind, the lower the output, the more flashes you can get at a given frequency.

Setting the Exposure

Once you have your output, frequency, and number of flashes set, you’ll need to set the exposure. You can determine the aperture by using a light meter, using the guide number table in your flash’s manual (f/stop = Guide number x ISO factor / Subject Distance), or simply by experimenting.

Keep in mind that if you have a portion of the frame overlapping (i.e. still part of the frame), the repeating flash may result in overexposure. For example: If you flash a still subject at 1/2 power two times, your exposure would be almost exactly like flashing that subject once at full power. This generally doesn’t affect moving subjects but is an important thing to consider when setting up your shot and calculating exposure.

The minimum shutter speed is determined by dividing the frequency of flashes into the number of flash frames (shutter speed = number of flashes / frequency (Hz)). For example: If your number of flashes per frame was 10 and the frequency is 5Hz, you would need a shutter speed of 2 seconds or slower. You can also use the bulb exposure if you are trying to time a particular action.

Setting Up for the Shot

Stroboscopic flash pictures work best in a dark setting. Because the shutter speeds can be very long, it’s also best to work on a tripod. You can trigger the flash from the camera’s hot-shoe, from an off-camera cable, or using a radio trigger. For this demonstration I used the latter. The main reason for this is when you fire the camera, it immediately fires the flash. By using the PocketWizard on the flash, I could delay when the flash was firing and manually trigger it as the object was in the frame. Here is a shot of the setup:

(1) Nikon SB-800 Speedlight (2) PocketWizard Plus II Transceiver with PC-sync connection (3) Camera with shutter release attached (4) Reflector on other side of “drop area” for fill (5) Black background (6) Step ladder to drop subject from.

I pre-focused to where the “drop zone” would be, and marked it on the floor with gaffer’s tape. I used a larger aperture to get a little leeway with the depth of field and to allow a longer shutter speed. Once the camera was set up and focused, I turned off all the lights and hit the shutter. I then dropped the object and triggered the PocketWizard as the subject passed through the frame. Here are the results:

Nikon D200, 35mm f/2, 3.0 sec @ f/11, ISO 100; Flash Setting: 1/32, 10x40Hz

Nikon D200, 35mm f/2, 3.0 sec @ f/11, ISO 100; Flash Setting: 1/32, 10x40Hz

Nikon D200, 35mm f/2, 3.0 sec @ f/11, ISO 100; Flash Setting: 1/32, 10x40Hz

Nikon D200, 50mm f/1.8, 3.0 sec @ f/5.6, ISO 100; Flash Setting: 1/64, 10x40Hz

You might have to do a lot of experimenting to get the results that you want, but stroboscopic flash can be a lot of fun. Hopefully the provided frequency, number of flashes, and power settings will give you a starting point.

Other Methods

There are also ways of achieving the same effect using traditional strobes or speedlights without a stroboscopic mode. You can always open the shutter and manually trigger the flash as many times as you’d like. Triggering systems like the PocketWizard Multimax transceivers feature a mode called multipop that allows a flash to trigger multiple times within an exposure.

There are also infrared and sound triggers available for high speed photography. These devices fire your flash when a particular action happens and can be a lot of fun to experiment with.

What you’ll need

First, you’ll need some sort of infrared filter. Because these filters block out all visible light, they are completely opaque. There are a variety of filters available of varying quality and wavelengths. The filter I use is a Hoya R-72, but other manufacturers, including Cokin & B+W, make similar filters.

Second, you’ll need a digital camera. When shooting with an unmodified digital camera, you are usually better off using an older model. As manufacturers create higher resolution cameras, they generally have to increase the effectiveness of the hot mirror in order to prevent infrared light from showing up in regular pictures. Infrared photos are still possible, but generally there will be much longer exposure times (Note: You can modify your digital camera to get around this, more on this later). The camera I will be using in this tutorial is a Nikon D50.

Third, you’ll need a good, sturdy tripod. When shooting infrared with an unmodified camera, the exposure times are usually very long (sometimes ranging in the seconds). Having a good tripod will prevent any blur from camera shake. I would also recommend using a wired or remote shutter release to trigger the camera and minimize vibration. If you do not have a shutter release, the self timer is another option. One thing to keep in mind, even though a tripod will help with camera shake the images will still be prone to motion blur if your subject(s) move.

One last thing I would recommend is using a lens with the IR index mark. Since infrared light is a slightly higher spectrum than visible light, you must offset your focus to compensate for this. The IR marking usually indicates how far you must offset your focus to compensate for IR light. Nikkor lenses indicate the IR index mark with a white dot to the left of the focus point, while Canon uses a red dot to the right of the focus point. Keep in mind that this mark is merely a guide and may not correspond to the wavelength of your filter so be sure to check focus accordingly. You can also try using hyper-focal distance if you plan on using a high aperture.

Shooting

The first thing I do before I set up an infrared shot is do a custom white balance with the IR filter on. If you leave the camera in Auto WB, or use the presets, your image will have a strong red tint. This is fine if you plan to convert your images to B&W but problematic for color images. I usually try to perform a custom WB from a patch of grass. This gives a unique look because it gives plants a cyan tint and turns the sky brown-ish. You can also use a custom WB tool such as a gray/white card or an Expodisc for different effects.

Once you have your custom WB set, remove the IR filter. Because the IR filter is completely opaque, it makes composing near-impossible. Set up the shot the way you normally would and focus. I generally take a “reference” shot at this point just to see how different the shot is. Once you have the focus locked, attach the IR filter to the lens. When you attach the IR filter, re-adjust the focus for the IR spectrum and lock the lens/camera into the manual focus position.

Once you take your first shot, check to make sure your image is in focus. Once your shot is in focus, the best thing to do is bracket your exposure. Since your camera has no way of metering for IR light and the amount of IR light varies, bracketing will give you the best possible exposure. Just be sure to watch for blown-out highlights!

Here are the results:

Reference Photo
Nikon D50, 35mm f/2, 1/160 sec @ f/11, ISO 200

Color Infrared Using Custom White Balance
Nikon D50, 35mm f/2, 1.6 sec @ f/11, ISO 200

Black & White Infrared Converted in Lightroom
Nikon D50, 35mm f/2, 1.6 sec @ f/11, ISO 200

Alternative Methods

Full Infrared Conversion

There are companies online that will convert your digital camera to a dedicated infrared model. What these companies do is remove the hot mirror from the imaging sensor and replace it with an infrared filter. They can also re-calibrate the focus of your camera so it focuses in the infrared light spectrum. The benefit of a full conversion is you no longer have to worry about long exposure times, you can freely compose the image as you would with a normal camera, and you would have full auto-focus capability. There are a couple of drawbacks to this procedure. First, it dedicates your camera to shoot only IR. Most importantly, modifying the camera voids your manufacturer’s warranty so if you decide to go this route, you do so at your own risk. More information on modifying can be found at Life Pixel.

Software alternatives

You can turn any normal image into an infrared image through the power of software. There are a number of Photoshop actions and plug-ins as well as Lightroom develop presets to mimic the effects of infrared photography. You can also use these tools to enhance your own infrared shots, or create your own custom black & white conversions.

The plug-in I use for infrared conversion/enhancement is Nik Color Efex. This software allows black & white, color, or thermal infrared conversions at the touch of a button. Here are some examples using the Nik Software to enhance the IR color out-of-camera image:

Nik Color Efex Pro 2.0 Infrared Color Mode 5

Nik Color Efex Pro 2.0 Infrared B&W Mode 2

 Hope you enjoyed this infrared tutorial – good luck!