The Digital World of Photography

The Digital World of Photography

by

Jeff Montanye

Lesson 329 – Flash : Advanced

Bounce Flash, High Speed FlashBalancing Flash with Ambient Light

Using a Bounce Flash

Why use an external Flash• First, even the smallest external flash is twice as

powerful as the retractable flash. Thus, you have more power for group portraits or subjects posed against the setting sun.

• Second, a shoe mounted flash is less prone to red eye because it is further from the lens axis.

• Third, external flashes may be used off-camera on stands or brackets for better modeling and macro work.

• Fourth, light modifiers, e.g., diffusers or bounce cards, may be employed for softer light.

• Fifth, flash metering is more acurate. • Finally, you may use special features of E-TTL

flash, e.g., high speed sync (FP Flash) or flash exposure lock (FE Lock), not available on most popups.

Home Made Bounces

Home Made Bounces

Master Your Camera's Flash

One technique when using a camera mounted flash indoors is to point it behind you. This only works if you have a flash with a rotating head. Stand with your back about three feet from a light-colored wall. This creates a very large light source.

Bounce off walls

Bouncing off walls can cause a color shift if the wall is not white. In this case, you will have to custom white balance the flash.

Bounce Flash

Bounce Flash

Good use of flash

Use a bounce flash

Remote Flash

Good use of flash

Off camera flash

Good use of flash

Off camera remote flash unit

High Speed Flash

Hi speed flashWhen fast shutter speeds are selected, the second shutter curtain begins closing before the first curtain fully opens. The illumination therefore only hits part of the film at normal flash settings. But the FP high-speed sync flash setting fires repeatedly at roughly 50kHz intervals during the exposure to achieve flash synchronization at all shutter speeds. The camera automatically reverts to normal flash firing when the shutter speed is set slower than the flash X-sync speed.

Focal Plane ShuttersAt fast shutter speeds (top) the second curtain starts

to end the exposure before the first curtain has fully opened so the two curtains form a slit traveling across the image sensor. Flash would only expose the area uncovered by the slit between the two rapidly moving curtains.

At the flash sync speed and slower (bottom) the second curtain doesn't start to close until the first one is fully open.

FP (Focal Plane) Hi speed flash

FP (Focal Plane) Hi speed flashHi-speed Flash Synchronization (FP flash)

Focal plane (FP) flash allows faster sync. speeds than just e.g. 1/200s. With very fast shutter speeds the opening between 1st and 2nd curtain is never as large as the whole film so a single flash burst would lead to a partially unexposed film. As a solution you have to have a constant flash light for the whole exposure time. Unfortunately modern flash units have a peak emisson characteristic so a single flash is not usable for this purpose. Today most manufacturers use a series of high frequent flash bursts (say 50 kHz) with reduced single light emission to simulate a (theoretically) long single constant flash burst.

FP (Focal Plane) Hi speed flash

FP flash

Good use of flashUse a flash capable of high speed (high sync) fast shutter speeds.

Slow Speed Flash

First or SecondFront or Rear

Curtain

1st or 2nd (front or rear) curtainMany cameras offer the possibility to synchronize either on the 1st or 2nd curtain. With 1st curtain sync. the flash is fired as soon as the 1st curtain is in upward position while with 2nd curtain sync. the flash is fired just before the 2nd curtain moves upwards. Obviously this means that the natural (ambient) light of a scene exposes the films either behind or before the flash burst. If you shoot e.g. a fast moving object with 2nd curtain sync. you'll get a blurred moving effect which will end in the (flash-) exposed object. With 1st curtain sync. it'll be the other way round.

Master Your Camera's Flash Modes

Slow Sync. 2nd Curtain. When the flash fires in normal Slow Sync mode, it fires right away, then leaves the shutter open for a while to expose more of the background. In 2nd Curtain exposures, the shutter opens for a while, then the flash fires at the end, right before the shutter closes.

1st or 2nd (front or rear) curtain

1st or 2nd (front or rear) curtainThe effects of 1st and 2nd curtain flash are most noticeable at slow shutter speeds. To accomplish this either use slow sync mode on your camera or use Shutter Speed Priority Mode and choose a slow shutter speed.

When to use front or rear?

Use rear sync when you want the motion to show before your subject.

Use front sync when you want the motion to show after your subject.

This rear sync image shows the motion before the subject was exposed by flash.

Front Curtain

Use rear sync when you want the motion to show before your subject.

Use front sync when you want the motion to show after your subject.

This rear sync image shows the motion before the subject was exposed by flash.

1st or 2nd (front or rear) curtainWhen using 2nd or rear curtain sync you may get two flashes, one at the beginning of the exposure and another at the end of the exposure.

This is due to TTL flash exposure. The first flash is simply a test flash which gives the camera a chance to calculate the flash exposure values before taking the picture.

Class Challenge

Set your camera to slow sync or place your camera in Shutter Priority mode.

Select a shutter speed of about 5 seconds.

Turn the room lights off and give the subject a flashlight. Have the subject walk back and forth across the room.

Use a tripod or hold the camera very still. Zoom out so the subject has room to walk from one end of the image to the other.

Have the subject start walking when you press the shutter release. Be sure to hold still during the entire duration of the exposure.

Try it on both first and second curtain modes.

Class Challenge

Try first and second curtain sync on a playing card.

Photograph moving match box cars

Balancing Flash with Ambient Light

Using

Aperture and Shutter Speed

Balancing Day and Night

Normally when you turn your flash on your camera will automatically set the shutter speed between 1/60 of a second.

To correct this you will need to place your camera into shutter or aperture priority mode.

Flash and shutter speed

Flash photography is different since it involves split-second bursts of light.

•A key point to remember in flash photography is that the shutter speed of the camera normally does not have any bearing on flash exposure - an exception being FP mode, mentioned later.

Light from a continuous source is affected by shutter speeds, but flash bursts are so brief - in the milliseconds - that a mechanical shutter mechanism has no way of limiting the amount of light from a flash unit that hits the film. Shutter speed only affects the amount of ambient light.

Flash and ApertureTTL controlled flash exposure is where your camera (and flash) work together in automatically controlling your flash’s output (as the camera reads it Through The Lens (TTL).  Since your camera is controlling the flash output to give you correct flash exposure, your choice of aperture and ISO (and the distance) doesn’t have a direct influence on flash exposure. Your flash’s power (ie, output) changes to give you enough light for correct flash exposure regardless of the aperture you choose. If you select a small aperture your flash will be more powerful. If you select a large aperture your flash will not need as much power.The aperture setting only effects the exposure if you are using your flash in manual mode.

Flash Sync SpeedThe faster the flash sync. speed ... ...the darker is the scene around your main subject because the ambient light has less influence on the exposure process. The effect is obviously dependent on the level of the ambient light. ... with a moving scene (or a static scene with moving objects) the less blurred are the objects which are not (significantly) exposed by the flash light. etc.

Flash – mixed with ambient light

When using ambient light, there are two main ways to control light to your camera 1) Shutter speed to control the duration of the exposure and 2) Aperture – to control the quantity of light that enters the lens.

Flash exposure, on the other hand, is controlled in a completely different way…

Balancing LightLets do an experiment:• Setup a subject that will be close to your camera with a background that extends back beyond your subject.• Set your camera to automatic and take a picture with flash.• Examine the shutter speed and aperture your camera selected.• Now, place your camera in full Manual mode and dial in these settings manually.• Turn flash off.• Take the picture.What does it look like? Too dark right?

Balancing LightLets move on to part two of the experiment:• Place your camera in Program mode and turn flash off.• Take the picture.• The picture should be bright however, if the shutter speed was too slow you may have some camera movement blur.• Examine the shutter speed and aperture settings the camera chose.• Set your camera to full manual and dial in these settings manually.• Turn flash on.• Take the picture.What does it look like? It should be correctly exposed.

Balancing LightFinally the last part of the experiment:• Manually change your shutter speed to various random settings.• You can control how dark the background is while keeping the foreground exposed properly with flash.

You can also try shutter priority mode, exposure and flash compensation modes as well.

Aperture and Flash

With TTL flash, aperture effectively becomes transparent.In other words, with TTL flash, our choice of aperture, (within reason), has no effect on flash exposure.  (This is also true for our choice of ISO.)

If we use a small aperture, the camera will compensate by using full flash intensity.

If we use a larger aperture, the camera will compensate by using less flash intensity.

Balancing Light• Shutter speed and aperture control the exposure of

your background.• only difference between these three pictures is the

shutter speed. The camera setting for the top picture is f-5 at 1/40th of a second. The foreground and background are both well exposed.

• The middle picture is f-5 at 1/160th of a second.• The bottom picture is f-5 at 1/250th of a second.• As you can see, the exposure on the flower is

about the same in all three pictures, but the background is getting darker and darker. The reason is because the aperture stays the same and my flash output is the same, the flower is not affected.

• But as the shutter speed gets faster and faster, I'm letting in less and less light, so I'm underexposing the background more and more. Shooting with a P&S is similar to the bottom picture. The shutter speed is too high so the background is under-exposed.

Aperture and Flash

1/125th @ f2.8 @ 800 ISO 1/125th @ f5.6 @ 800 ISO

The difference between the two pictures is that the larger aperture on the left over exposed the background window.

Aperture and FlashAnother way to achieve the proper background exposure would be to spot meter on the background window and use fill flash.

To spot meter on the background you will need to use the AEL button or the camera will focus on the background as well.

Flash and Shutter SpeedThe total area for the ambient light increases as you consider more time horizontally, due to a longer shutter opening. The area (exposure) for the flash doesn't change so long as the exposure is at least 1/1,000 second to capture it all.The exposure from ambient light increases as exposure time (flash sync speed) gets longer, but the contribution from the flash stays the same. One uses smaller apertures with longer exposures, which keeps the ambient exposure constant but requires more power from the flash to keep up.

Balancing Day and Night

Every SLR camera has a top sync speed for flash. At this speed, the camera can still allow for the entire burst of flash to expose the film before the shutter closes. These speeds will vary from camera to camera but usually go no higher than 1/250th of a second.However, just because this is the suggested flash synchronization speed, it does not mean that it is your only option. At 1/250th of a second, very little available light in a standard indoor environment is permitted to reach the film – and here is your first mistake.

Class Challenge

Flash and Metering

Flash and Spot Metering

Some cameras allow you to use your spot meter to adjust the flash .

Flash Exposure LockA few cameras have flash exposure lock that works much like AE lock and is used to properly expose off-center subjects. To use it, you center the main subject and press the shutter button halfway down. The flash fires a preflash to determine the best exposure and then locks it so you can recompose the image before pressing the shutter button the rest of the way down to take the picture.

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