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Flash 101 > 2 - Advanced Flash

1 - Three Orientations

Before you read on, orientate your thinking about flash in the following three ways.

They're obvious, but its good to set them out all at once.

Way #1 - Two Sources of Light

There are two sources of light—the flash—and the ambient light.

Way #2 - Two Places

There are two places in the scene—the subject—and the background.

Way #3 - Exposure in Each Place

Subject Exposure

The subject is exposed by the flash.

The flash changes the duration of its "blink."

The blink at full power lasts for about 1/1,000th of a second.

When photographing a subject up close, the flash doesn't have to produce much light.

The flash duration may be about 1/40,000 of a second.

Background Exposure

The background is exposed by the ambient light.

The background is brighter with slow shutter speeds.

Its darker with faster shutter speeds.

4 - Summary

Two Sources of Light:

Flash Light

Ambient Light

Flash Light

Expose the:

Subject

With Different

Flash Durations

Ambient Light

Exposes the:

Background

With Slow or Fast

Shutter Speeds

2 - Flash Exposure Measurement

Several topics are covered below.

How Is the Flash Measured?

The light from the flash is measured in one of two ways.

Way #1 - Older Flashes

The flash may send out a preflash to determine how long the flash should be on.

The preflash is done just before the shutter opens.

The preflash is almost imperceptible, buy it may cause some people to blink.

Way #2 - Newer Flashes

The light from the flash is measured when the shutter is open.

What Part of the Scene Is Measured?

The center of the frame is where your flash is measuring./p>

If the subject is not in the center, the exposure may be off.

Your flash may have a function similar to automatic exposure lock for the flash.

IIn Nikon cameras, it's called flash value lock.

In Canon cameras, the function is called flash exposure lock (FEL).

Also, your Canon camera may have AIM (Advanced Integrated Multi-point Control System).

The flash will measure the light where the focus point is located.

So, if you have an off-center subject, change the focus point to where the subject is located in the frame.

Matrix & Evaluative Metering

Your flash may perform better when matrix metering (Nikon) or evaluative metering (Canon)./p>

These metering methods allow the camera and flash to measure:

• The light behind the subject, the ambient light.

• The light being reflected back from the subject to the camera.

Center-weighted metering, and especially spot metering, do not permit the measurement of the ambient light.

Synch Speed

What Is It?

Your flash can't operate at a shutter speed higher than the flash synch speed.

The flash synch speed varies depending on the camera model.

The range is from 1/60th to 1/250th.

Why Is It Important?

Your camera probably has a focal plane shutter.

There are two curtains that travel up or down.

The curtains both open and close at the same rate of speed.

Different shutter speeds are obtained by opening the second curtain at different points in the open-and-close cycle of the first curtain.

Above the Synch Speed

At shutter speeds faster than the synch speed for your camera, both curtains are starting to close.

They make a narrow slit.

The light from your flash won't reach the entire sensor.

The curtains are blocking a portion of the light.

Synch Speed & Slower

At the synch speed, and at slower shutter speeds, the flash is able to fire when both curtains are both completely open.

The first curtain opens completely before the second curtain starts to close.

The flash fires before the second curtain starts to close.

Flash at Shutter Speeds

Above the Synch Speed

Your flash may have a feature that blinks the flash repeatedly.

So, as the above described slit moves, the blinks of flash eventually reach the entire sensor.

When using this feature, the power of the flash is greatly reduced.

Use this feature for portraits, in sunlight, when you want to use a wide lens opening to reduce depth-of-field.

That is, you set a fast shutter speed, which permits the camera to select a wide lens opening.

The subject must be close to the flash.

3 - Camera Exposure Modes

Your camera and flash combination perform differently depending on which camera exposure mode you select.

Check your flash instruction manual.

The typical flash does the following.

Auto & Program Exposure Modes

In Bright Light - Outside

When using the Auto or Program camera exposure modes, in bright light, the flash:

• Lets the sunlight illuminate the subject.

• Brightens the shadows on the subject.

This is called fill flash.

Go to Fill Flash.

In Dim Light - Indoors

When using the Auto or Program camera exposure modes, in dim light, the flash:

• Illuminates the subject.

• Won't use a slow shutter speed to brighten the background.

The background will be dark.

Blur When Using Auto or Program

Because the camera selects a fast shutter speed, blur from camera shake or from subject movement is unlikely.

A/Av & S/Tv Exposure Modes

When using the aperture-priority or shutter-priority exposure modes, the camera will try to make the background brighter.

It will select a slower shutter speed, if possible.

Blur with A/Av

Let's say you're using the aperture-priority exposure mode.

If you set the lens opening to a physically small setting, such as f/22, the camera will select a slow shutter speed.

There may be blur from camera shake and subject movement.

Blur with S/Tv

Let's say you're using the shutter-priority exposure mode.

Generally, if you set the shutter speed below 1/60th, there may be blur from camera shake and subject movement.

Bad & Good Blur

If blur is detrimental, use a tripod and ask your subject to not move.

However, some blur may be beneficial.

You'll have a frozen image of the subject, mixed with a blurred image of the subject, all in one photograph.

This may make a kick boxer look more active.

Finally, blur may not matter.

If the subject is stationary, any blurred movement in the background may be okay.

Summary of the Above

Exposure Modes

Mode

Shutter Speed

Background

Blur*

Auto & P

Above 1/60th

Darker

Unlikely

A/Av or S/Tv

May Be < 1/60th

If So, Brighter

Possible

Night Portrait

Below 1/60th

Brighter

Likely

* From camera shake and subject movement

Manual Exposure Mode

With Indoor Ambient Light

Manual exposure mode gives you control over the balance between the indoor ambient light and the flash.

You adjust the shutter speed to make the ambient light brighter or darker.

The flash exposure is determined by the lens opening.

Do the following.

Set Up: Shutter Speed & Lens Opening

Determine the lens opening when the shutter speed is at 1/60th.

1) Use an ISO from about 400 to 800.

2) Set your exposure mode dial to Manual (M).

3) Set the shutter speed to 1/60th.

If your camera has a single knob, usually, turn it to change the shutter speed.

If your camera has two knobs, one of them will change the shutter speed.

4) Set the lens opening.

If your camera has a single knob, look for the button with an aperture icon.

Press and hold the button, and turn the knob.

If your camera has two knobs, one of them will change the lens opening.

Move the knob to where the green or black dot on the exposure "number line" is in the center.

-2 -1 0 +1 +2
                       

If you can't move the dot to the center, increase the ISO.

Set Up: Flash

1) Set the flash to TTL mode.

2) Leave the lens opening where you set it.

2) Select the shutter speed using to the chart below.

By changing the shutter speed, you can make the ambient light brighter or darker.

You can use a shutter speed between the shutter speeds in the chart.

Typically, you want the ambient light to be about one stop darker than the the ambient light.

Use 1/90th or 1/125th.

At this shutter speed . . . the background brightness is . . .
1/30th

. . . one stop brighter than the flash.

This is fill flash.

Camera shake and subject blur are

possible.

1/60th . . . the same as the flash.
1/90th . . . darker than the flash.
1/125th* . . . one stop darker than the flash.
1/250th** . . . two stops darker than the flash.

*  Not all cameras support using 1/125th with flash.

**  Very few cameras support using 1/250th with flash.

LCD v. Monitor

When judging your results, when you first try this, use your computer monitor.

Don't rely on the LCD screen display on your camera.

Compare how the best example looks on your monitor with how it appears on your camera.

4 - More about Shutter Speed

Only So Fast

Your camera's shutter blades must be out of the way when the flash goes off, obviously.

Above a certain shutter speed, the blades will block some of the light from the flash.

This certain shutter speed is called the synch speed.

It varies from 1/60th to 1/500th, depending on the camera model.

Do the following to see the synch speed.

1) Turn off your flash.

2) Set the camera exposure mode to S or Tv.

3) Set the shutter speed to 1/2000th.

4) Turn your flash on while watching the shutter speed on the LCD screen.

5) The shutter speed will change from 1/2000th to the flash synch speed for your camera.

But You Can Go as Slow as You Want

The shutter speed can't go above the flash synch speed.

However, you can use any shutter speed below the flash synch speed.

This is done when photographing indoors.

When you use a slower shutter speed, such as 1/30th, the ambient light will be included in the exposure.

Think of shutter speed as a "slider" for the exposure of the background.

 

1/30th

1/60th

1/125th

1/250th

Background Brightness

       

Again—slow shutter speeds are used with flash—indoors.

1/250th - Dark Background

Let's say your camera's flash synch speed is 1/250th.

At that shutter speed, very little ambient light can reach the sensor.

The background will be dark.

1/30th - Brighter Background

Using a slow shutter speed with flash is called slow shutter sync or dragging the shutter.

If you use a shutter speed of 1/30th, or thereabouts, the shutter stays open long enough for the ambient light to make a contribution to the exposure.

The background will be brighter.

Setting a Faster Shutter Speed

Use the Auto or Program camera exposure modes.

The camera will select the synch speed, the fastest shutter speed when using flash.

If not, set the camera exposure mode to S or Tv.

Select the flash synch speed.

Setting a Slower Shutter Speed

Set the camera exposure mode to S or Tv.

Then, set a slow shutter speed.

When using A or Av indoors, if you set a small lens opening, the camera will select a slow shutter speed.

You can also use the camera exposure mode called Night Portrait or Twilight Portrait.

If the Shutter Speed Won't Go Below 1/60th

In the menu for your camera, there may be a setting called Flash Shutter Speed, or something similar.

The default setting is often 1/60th.

If so, you can't go below 1/60th when the flash is turned on, and if you're using the P or A/Av camera exposure modes.

If you want to use a slower shutter speed than 1/60th, go to Flash Shutter Speed and lower the shutter speed.

Or, use the S/Tv camera exposure mode.

When Using Flash at Slow Shutter Speeds
Camera Shake

Camera shake may become visible.

Lights in the background may appear as streaks.

Use a tripod.

Subject Blur

If the subject is moving, there may be a frozen image of the subject amongst a blurred image of the subject.

If there's movement in the background, the motion may be blurred.

5 - Why Can't the Flash

Illuminate the Background?

When you bounce the flash off of a ceiling, you may illuminate the background somewhat.

Most often, though, the background is illuminated by the ambient light.

Why doesn't the flash reach the background?

Let's say you're helping Tyler with his science project about predators.

You're helping him photograph a toy mouse and a hungry rubber snake.

The mouse is two feet from the flash.

The snake is three feet from the flash.

Tyler's dog is sleeping four feet away.

Flash

Is

Here

Mouse

Snake

Dog

2' Away

3' Away

4' Away

You press the shutter release.

Imagine:

• A point on your flash.

• There are photons emanating from this point.

• They're spreading out as a cone of light from the point.

• The cone of light, from the view of the mouse, appears as an expanding circle.

When the expanding circle reaches the mouse, there are 900 photons per square millimeter on the surface of the circle.

(There are, of course, many more photons than 900.)

The camera sets the exposure, and the mouse is well-exposed.

The circle keeps expanding toward the snake.

When it reaches the snake, the circle is much larger in diameter.

There are now only 100 photons per square millimeter, instead of 900.

The light is 1/9th dimmer than the light at the flash.

The 1/9th value is from the inverse square law:

1/distance2

 

Exposure

Set for the

Mouse

 

 

Flash

Is

Here

Mouse

Snake

Dog

2' Away

3' Away

4' Away

1/4th the Light

1/9th the Light

1/16th the Light

6 - ISO = Distance

You can use ISO to make the light from your flash go farther.

Think of ISO as the distance control for your flash.

At a low ISO, the light doesn't go very far.

At ISO 1600, the light goes much further.

Let's say you're photographing a school play.

At ISO 100, the flash will travel only for a short distance.

The bald head of the man in front of you will be well exposed.

At a higher ISO, the flash may reach the stage.

Summary

ISO

100

200

400

800

1600

Flash

"Power"

Less       More

7 - A Faster Synch Speed

Is Better for Fill Flash

Let's say your camera has a flash synch speed of 1/60th.

And, you're photographing a cowboy in Arizona at noon.

You need to use fill flash to light the cowboy's eyes under the brim of his hat.

The sunlight is bright.

At the flash synch speed of 1/60th, and at ISO 100, the lens opening will be about f/22.

You'll have lots of depth-of-filed at f/22.

If you would prefer to have less, you can't.

The flash requires a shutter speed of 1/60th.

You can't move the shutter speed up to 1/250th.

If you could, at 1/250th, the lens opening would be f/11.

There would be a little less depth-of-field.

So, if you do lots of outdoor portraits in the sun, such as weddings, get a camera with a flash synch speed of 1/250th.

8 - Flash Exposure Compensation

What Is It?

You may have used exposure compensation to vary the exposure.

Flash exposure compensation is similar.

It changes the brightness of your flash.

3 Situations

There are three situations where flash exposure compensation will be useful.

1 - Fill Flash Too Bright

Often, when using fill flash to brighten shadows on a sunny day, the shadows are too bright.

Reduce the brightness to -0.5 to -1.0 by adjusting the flash exposure compensation.

Go to Fill Flash Too Bright?.

2 - Create Catch Lights

To create catch lights, reflections in eyes, set the flash exposure compensation to -1.5 or -2.0.

Catch lights add personality to portraits, especially when the eyes are dark colored.

Go to Add Catch Lights.

3 - Non-average Toned Subject

If your subject is light toned, set the flash exposure compensation to +1.5 or thereabouts.

If your subject is dark toned, set the flash exposure compensation to -1.5 or thereabouts.

Does Exposure Compensation

Affect the Flash?

On Nikon cameras, setting the camera's exposure compensation affects both:

• The exposure of the ambient light.

• The brightness of the flash when using iTTL or Auto Aperture.

9 - Color

There are several ways you can improve the color when using flash.

Slightly Blue?

The color of the light from many flashes is slightly blue.

If your flash produces blue light, try using the flash icon when setting the white balance.

Shadows Too Blue with Fill Flash?

On a sunny day, shadows are cyan colored (blue/green).

That's because the shadows are illuminated by the cyan-colored sky.

When you brighten these shadows with your flash, they become warmer in color.

If you would like to make them even warmer, put a warming filter on your flash head.

Try a Rosco Cinegel 3409.

Don't Like

Green or Orange Backgrounds?

Green from Fluorescents

Let's say you're photographing in a classroom or office.

The lights above are probably fluorescents.

They produce green-colored light.

Your flash will overpower this green light.

But, the background will be green colored.

And, shadows will also be green.

To eliminate the green, do the following.

1) Put a Kodak 30G filter, a Rosco Cinegel 3304 filter, or the equivalent, on your flash head.

Now, all of the light sources are green.

The fluorescents are green.

The flash is green.

2) On your camera, change the white balance to the fluorescent tube icon.

Now, your camera is removing the green from the fluorescents and from your flash.

Orange from Light Bulbs

(Including Halogen)

Let's say you're photographing a wedding reception.

The lights above are incandescent bulbs.

The walls are washed with Halogen spot lights.

These lights all produce orange-colored light.

Photographers call this tungsten light.

That's because the filaments in light bulbs were made from tungsten.

Your flash will overpower the orange tungsten light.

However, the background will be orange colored.

And, shadows will also be orange.

To eliminate the orange, do the following.

1) Put a Kodak 85B filter, a Rosco Cinegel 3304 filter, or the equivalent, on your flash head.

Now, all of the light sources are orange.

The lights are orange.

The flash is orange.

2) On your camera, change the white balance to the light bulb icon.

Now, your camera is removing the orange from the Incandescent lights and from your flash.

Filters for Your Flash

You can get above color-correction filters from the sources below.

Flash Manufacturer

The manufacturer of your flash probably offers the filters.

Other Sources

 ExpoImaging Rogue Flash Gels Color Correction Kit 

MPS Sticky Fill Flash Correction Filters

photogels.com

Rosco

You can also use filters made by Rosco.

• Use a Rosco Cinegel 3304 (Tough Plusgreen), which is equivalent to a Kodak 30G filter, to convert a flash to a florescent color temperature.

• Use a Rosco Cinegel 3401 ( (Roscosun 85), which is equivalent to a Kodak 85B filter, to convert flash to a tungsten color temperature (3200°K).

• Use a Rosco Cinegel 3409 (Roscosun 1/4 CTO), which warms the light by 1000K, to make the light from a flash less blue.

Fore information, go to Rosco Guide to Color Filters (PDF), Roscolux-Supergel Swatchbook.

Filter Tip

If your flash doesn't have a filter holder, use real gaffer tape to attach the filters to your flash.

Don't use duct tape.

Preset or Custom White Balance

You may want to use a wide lens opening to reduce depth-of-field.

Let's say you're at f/1.4.

The flash won't have to produce much light at that lens opening.

And, with such a wide lens opening, the room light will mix with the light from the flash.

If the room lights are incandescent, your photographs will be somewhat orange.

To remove the orange, set a preset or custom white balance.

10 - Extension Cord

Size of the Light

The size of a light source is important.

By using a separate flash, you can control the size of the light source.

If you want contrasty light—use direct flash.

If you want brighter and softer shadows—use bounce flash.

Direction of the Light

The direction of the light is also important.

If you get an extension cord for your flash, and if you have a strong arm or an assistant, you can control the direction of the flash.

Let's say you're photography a family event.

If you want to:

• Minimize the wrinkles on the face of the family matriarch, hold the flash nearer your camera.

• Deemphasize the bald head of Uncle Percy, lower the flash somewhat.

• Make the twins more three dimensional then hold the flash up to one side.

The shadows on their faces will make them less flat like a mug shot.

• Use sidelighting for the host's collection of antique boomerangs.

The carving in the wood will be more evident.

Sidelighting highlights texture because it produces shadows.

• Make the kid who kicks you every time you go by, into a monster, by holding the flash below his face, pointed up.

11 - You Can Still Get Red Eye

With a Separate Flash

Normally, the flash mounted on your camera's hot shoe is far enough from the lens axis to prevent red eye.

However, if you're photographing a distant subject, you may get red eye.

That's because, at that distance, there's little difference between the lens axis and the flash.

12 - Guide Numbers

When shopping for your flash, you may have encountered a specification called guide number.

The guide number is a measure of the power of the flash related to distance.

The guide number is based on three other values.

• ISO, usually 100

• Distance measured in feet or meters

• Where the flash is zoomed, i.e., wide or telephoto

When comparing the guide numbers of two flashes, make sure the above three values are the same for both guide numbers.

Guide numbers were used to determine exposure.

Simply divide the guide number by the distance to get the lens opening.