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SWC Photo & Digital

Flash Information

All Classes

Bounce, Fill Flash, & Long Sync Speed Notes

Before working with flash, realize that the camera's built-in meter will inform you only about the ambient light metering, not the flash.

Basic Terminology:

Sync Speed: The fastest shutter speed your camera can use with flash. On a 35mm SLR

camera this is usually 1/60 or 1/125. On cheaper digital SLR’s it is usually 1/125.  On higher end digital SLR’s it is 1/250.  The number is usually red or has a lightning symbol

next to it (on film cameras).

Built In Flash: Common on Point and Shoot Cameras and some 35mm SLR’s. This flash is typically not adjustable and presents some problems such as over exposure on a subject and dark shadows behind the subject even if there isn’t a wall up close.

Hot Shoe Mounted Flash: These include basic flash units, dedicated flash units, automatic flash units, and TTL flash units.

Automatic Flash: Determines exposure for you. This is a common for built in flash units.

Other flash units have automatic ranges that help do some of the work for you.

Dedicated Flash: Designed to go with a specific camera. Mixing dedicated flashes with the wrong camera can result in short circuiting the equipment!

Through The Lens Metering (TTL): A sensor inside the camera automatically reads the burst of light’s reflection of the subject. This system is not perfect…usually go for simple subject scenes and subjects that are not highly reflective. Also, cheaper TTL units do not balance ambient light with flash. TTL sensor meter reflected light and have similar problems to light meters that are built into your camera.

Flash Meter: This is an electronic meter that measures the exposure in a specific area given by flash. These units are extremely precise and nice, but also expensive.

Slave Unit: These include flash sensitive, infrared sensitive, and radio controlled units.

They are used to trigger a flash that is not directly connected to the camera.

Guide Number (GN): A measurement of the power or intensity of the flash.  Low Guide Numbers (GN) indicate a weak or less powerful flash than one with a higher GN.

-usually measured at ISO 100

-Guide Number = distance x f-stop

-For example:  a GN of 100 means that you could use f-4 at 25 feet from subject.

-This is usually a very optimistic measurement for the flash at full power.

Sync Cord: Connects an off-camera flash to the camera so that the flash will be triggered by the shutter release.

Fill in Flash: Adding flash light to the subject to separate the subject from the background, compensate for backlit scenes, or filling in dark shadows on the subject.

Flash Fall-Off (Inverse Square Law)

As an object is placed further away from the flash, less possible light can hit the object.

Thus, distance helps determine exposure from a flash light source. As the distance from the flash doubled, the exposure of the flash is 1/4 it’s original amount.

Methods of using more versatile flash:

• Scotch Tape as a diffuser on built in flash units

• Off camera flash with either a sync cord, slave, or bracket system

• Professional light modifiers (usually diffusers)

• Homemade light modifiers

General Considerations for Flash:

1.Regardless of your flash, it is recommended that you test it and get to know its accuracy.  Also, it is recommended that you do a bracket to give you a varying about of fill flash on the subject.

2.Keep in mind that flash exposure is controlled by aperture, not shutter-speed.

3.Flashes are only as powerful as their guide number and distance to subject.

4.Non dedicated flashes on digital cameras tend to underexpose when using the flashes recommend settings.  For regular straight on flash with a non-dedicated flash, consider opening up your aperture one stop over whatever the flash tells you to do.  At SWC photo, we have found this to be common for the Vivitar, Metz, and Sunpack flashes.

METERING WITH FLASH (Basic Straight On Flash)

Operating a Flash with a manual calculator dial:

1. Set the ISO on the flash unit

2. Set your shutter speed for the flash sync speed

3. Set the distance from flash to subject

4. Set the lens on the aperture that is opposite the distance you chose above.

Operating a Flash with automatic exposure settings:

1. Set the ISO on the flash unit.

2. Set your shutter speed for the flash sync speed.

3. Set the automatic mode based on the range of distance that you will have between

your flash and subject.

Bounce Flash

Goal:  Get more diffusion than straight on flash, create a larger light source, light backgrounds to some degree as well as subject.

This is an effective technique when you want to light your subject and surroundings with a more diffused light source than a straight on flash.  As with most situations, it has its limitations.

Angle of Incidence & Angle of Reflection

Directions for Manual Bounce Flash:

1.Make sure that your camera ISO and Flash ISO match.

2.Unless you have a fancier dedicated flash, then set both your camera and flash to manual mode. 

3.Make sure your shutter-speed is your sync speed for your camera.

4.In most cases, remove any diffusion dome from the flash.

5.Use the flash exposure dial on the back of the flash to figure out the necessary aperture.  Your distance to subject is based on the distance to bounce surface plus the distance from bounce surface to your subject.

6.You will need to compensate for the bounce. Exposure loss.  Here are some general guidelines for your compensation adjustments.

If your surface is shiny and within six feet of your subject, compensate by adding two stops exposure over the flashes listed exposure.  In other words, open up your aperture by two stops.

If your surface is dull and within six feet of your subject, compensate by adding   three stops exposure over the flashes listed exposure.  In other words, open up your aperture by three stops.

If your bounce distance is less than six feet away, then add less exposure than listed above.

Realistically, it is hard to bounce off of surfaces more than six feet away from your subject. 

6.  Bracket your exposures.


ISO is 200.

Sync speed is 1/125.

Distance from flash to ceiling is 6 feet.

Distance from ceiling to subject is 6 feet.

Total distance for flash is 12 feet.

Flash calculator dial says that at this ISO and distance, I should use an aperture of f-11.

My ceiling is shiny, so I compensate by opening up the aperture two stops to f-5.6.

My bracket of exposures would be the following:  1/125 @ f-4, 1/125 @f-5.6, 1/125 @ f-8.

Note:  Fancier Dedicated flashes such as the Nikon SB800 & 900 can actually compensate for bounce, and usually have better results when you keep the camera in an automatic mode instead of manual mode.

Fill Flash + Ambient Light (Balancing both exposures)

Goal:  You want to fill in shadows, balance ambient light and flash, and most folks would never have known that you used a flash.

This scenario is typically a scene where the background has more light than the subject in the foreground.  You want to use normal exposure to capture the background, and flash to fill in the shadows of the foreground subject.

The following procedures work best with a flash that has adjustable power settings.  Fill Flash is typically done in outdoor daylight situations.  For low light situations or interiors, see the section called Long Sync Speeds.

Manual Flash Mode Directions:

1.Use your Camera in Manual Metering Mode

2.Set your Flash to manual mode.

3.Set the Flash ISO to match your Camera ISO.

4.Know your Camera’s Sync Speed.  Set your shutter-speed to the sync speed.

5.Point your camera at the background and meter the scene.  Ideally, you would meter off a graycard.  Look at your Camera’s lightmeter and find the aperture that matches your shutter-speed for correct exposure without flash.  Keep those settings on your camera.

6.Measure the distance between flash and subject.

7.On your Flash, look at the find the aperture that is across from the distance measured.  Usually, it will not be the same as the aperture you got when metering the background.

8.Lower the power settings until the distance does match the aperture you set from the background exposure.

Note:  If the flash is still too strong, you will need to increase your distance between Flash and subject.

Note:  You may need to increase exposure slightly if using a diffusion device on the flash.

9.Take the picture.


ISO is 100.

Sync speed is 1/125

Background exposure is f-8 @ 1/125

Distance between Flash and subject is 5 feet.

Aperture that matches your distance is f-11 at full power.

Reduce Flash power to 1/2.  This allows the aperture to match your distance at f-8 instead.

Take the picture.

TTL Flash Mode with Camera Dedicated Flash Directions:

TTL flash (with the camera in manual metering), will make the necessary adjustments mentioned above.  If using a Nikon Speedlight such as the SB-800, you will want to use TTL-BL in most cases. 

Nikon has I-TTL, Canon has E-TTL

If photographing a scene outdoors as mentioned above, be aware of how much light is hitting the subject.  The more your subject is in the shadow, the more you rely on the TTL-BL to do the work.  If your subject is just slightly darker than the background, then you may find that you want to lower your flash exposure compensation by about -1 to -1.7 stops while still exposing properly for ambient light.

Dragging The Shutter (Front Curtain Slow Sync)

Goal:  Increase ambient light exposure.

1.Meter the scene for flash (distance to subject). 

2.If you have the option on your camera, keep your camera on the regular flash setting.  This is also the default setting.

3.To increase ambient light exposure, use a slower sync speed.  Typically, as long as you don’t go below 1/15 of sec with a still subject and tripod, you can avoid motion blur. 

4.If you want to play with motion blur, try not using a tripod, and even slower shutter speeds (probably 1/8 sec or slower depending on conditions. 

5.Adjust apertures to help with exposure issues.

  1. 6.Not possible in bright light.  Do this in early morning, evening, interiors, or nighttime but with available light.

Rear Curtain Slow Sync

Goal:  Use motion blur with flash for creative results.

1.To achieve motion blur, delay the flash to the end of the exposure with settings such as slow sync if you have this possibility.

2.Put your camera on Rear Curtain sync in the flash menu (if you have this option).

3.Try 1/15 of a sec or slower.  This is experimental, so try.

4.Adjust apertures to help with exposure issues.

5.Not possible in bright light.  Do this in early morning, evening, interiors, or nighttime but with available light.


You Tube Movies

Website Links

photo by Xavier Bencomo, front curtain slow sync

photo by unknown,  rear curtain slow sync (probably)

Example:  Fill Flash

Left:  Regular Exposure / Right:  Dragging The Shutter

Photographer:  Dave Wuchner

Climber:  Chris Nance

Example of Slow Sync Flash

Aperture:  f-2.8,

Shutter Speed 1/30 sec

Example:  Slow Sync

Flash Comparisons Using Different Methods of Diffusion

Diagram:  Bounce Flash

Notice that of all the diffusion methods show,  bounce flash is superior for avoiding cast shadows...especially when your subject in close to a wall.

Example of Fill Flash