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Thursday

FLASH PHOTOGRAPHY 101 - A BEGINNER’S GUIDE • 4 of 4

Guide Numbers and High Speed Sync

With our fourth and final lessons, Mark Jordan Photography is offering you two lessons for the price of one! First we'll discuss Guide Numbers, followed by a quick lesson on High Speed Sync.

Guide Numbers

The guide number for an electronic flash is a way of quantifying its maximum output in terms that a photographer can relate to – aperture and distance. The guide number (GN) is the product of the aperture (f/ stop) and distance (from flash to subject) combination that will result in enough light for proper exposure.

The basic formula is:

GN = Aperture x Distance

By rearranging this formula we can also conclude that

Aperture = GN / Distance
Distance = GN / Aperture

The three most common ways to use the guide number are:

Determine the proper aperture for a subject at a given distance when using manual flash. Example: Your flash has a GN of 160 feet and your distance is 20 feet. The proper aperture is f/8 (160/20=8 ).
Determine the maximum distance a flash will properly illuminate the subject at a given aperture. Example: Your flash has a GN of 160 feet and you want to use f/8. The maximum distance is 20 feet (160/8=20).
Comparing the relative power of different flash units (higher guide numbers indicate more power). But make sure you’re comparing apples to apples, especially concerning point #2 below.

This all seems pretty simple, straight-forward and foolproof, right? Well it is, sort of. There are at lease six important points to keep in mind:

A guide number must contain a distance unit (generally meters or feet) and an ISO value. Most advertised guide numbers are in meters at ISO 100, but it’s critical to know for sure. Some times they’re listed in feet, and sometimes they’re listed at ISO 25 or something else. To convert meters to feet, multiply by 3.3.
The guide number changes when you zoom the flash head. For example, the 580EX Speedlite has a GN of 58 meters when zoomed to 105mm coverage, but this drops to 28 meters when zoomed to 28mm coverage.
The guide number increases as you increase the ISO. Doubling the ISO increases the GN by a factor of 1.4. Going from ISO 100 to 400 doubles the GN.
Adding any kind of light modifier (diffuser, bouncer, umbrella, etc.) to the flash unit will significantly reduce the effective guide number. Published GN specifications apply only to undiffused, direct flash.
The GN will be significantly less when high speed sync (FP Flash) is used. More on that later.
Since the above caveats can make these calculations a bit complicated, it’s a good idea to pay attention to the distance scale on the back of your flash unit, if it has one. The flash will do the calculations for you, factoring in the aperture, ISO and HSS, and give you a good estimate of your range. Keep in mind that the flash doesn’t know when you have a diffuser attached, so if you use one of those things, all bets are off.

Now on to Part 2

High Speed Sync

- a.k.a. FP Flash -

Every SLR camera with a mechanical shutter has a maximum flash sync shutter speed (1/200 or 1/250 on current Canon DSLRs). This has to do with the way focal plane shutters work.

At slower shutter speeds, the first curtain opens, the flash fires, and after the specified time duration, the second curtain closes behind it. At shutter speeds faster than flash sync, the second curtain begins to close before the first curtain is completely open. The second curtain follows the first across the frame, exposing only a slice of the image at any given moment. Firing a flash during this process would illuminate only part of the image. Generally this limitation only becomes an issue in situations where you have a lot of ambient light and want to use a wide aperture, such as when using fill flash for outdoor portraits.

Canon’s FP Flash system enables the use of flash at high shutter speeds. With FP Flash, the flash unit fires a burst of low-powered flashes at 50 khz (that’s 50,000 flashes per second) lasting throughout the duration of shutter curtain movement. For all intents and purposes, the flash unit becomes a continuous light source that lasts a very short time.

The only drawback of this approach is its inherent inefficiency and loss of range. Since the flash is firing while the shutter curtains aren’t completely open, not all of the light that goes through the lens reaches the sensor.

The illustration below is from the Canon Flashwork online brochure.

Just how much range is lost? Official Canon documentation is sorely lacking in this regard. Instruction manuals for Canon Speedlites only tell you to look at the distance scale on the back of the unit. The manual for the Sigma Super flash unit has a table to quantify things, so I’ll use that for the purpose of discussion. I don’t honestly know how closely this might match up with data for Canon Speedlites if such data existed.

In the image below, the top table shows “normal” guide numbers for the Sigma EF-500 DG Super, at various power levels and zoom settings. The lower table shows guide numbers at full power for FP Flash at various shutter speeds and zoom settings.

Suppose that you have “sunny 16” ambient light (1/100 shutter speed & f/16 at ISO 100). With normal flash, zoomed to 105mm coverage, depending on your camera’s sync speed, you could use:

1/200 & f/11 for a range of 4.55 meters (50/11). This is your maximum range with a 5D, 10D, 300D or 350D.
1/250 and f/10 for a range of 5 meters (50/10). This is your maximum range with a 20D or 30D.
1/500 and f/7.1 for a range of 7 meters (50/7.1).This is your maximum range with a Nikon D70s.

I threw in the 1/500 example because Nikon has a DSLR with a 1/500 flash sync speed, and I really wish Canon would step up to the plate in this regard. But I digress. The point here is to show the advantage of a faster sync speed.

But when you study the numbers for FP Flash, the first thing you realize is that the guide number is cut in half each time the shutter speed is quadrupled. So your effective distance doesn’t change as you shift exposure settings in a given ambient light situation, matching faster shutter speeds with wider apertures. This makes sense when you think of FP Flash as a continuous light source. For example:

Using the guide numbers for FP Flash and 105mm zoom (right side of the lower chart)

1/250 and f/10 gives you 2.5 meters (25.0/10)
1/1000 and f/5 gives you 2.5 meters (12.5/5)
1/4000 and f/2.5 gives you 2.5 meters (6.3/2.5)

So there’s no single thumb-rule that says how much distance you lose with FP Flash. It depends on the flash sync speed you start with, at least with the Sigma unit. But the loss is significant enough to conclude that using FP Flash when you don’t need it will drain your batteries faster and make recycle times longer, so it makes sense to use normal flash whenever you don’t need the background-blurring effects of a wide aperture.

Since FP Flash is less efficient and gives you less range, it is advantageous to choose exposure settings that do not require it unless you specifically need it for the reasons mentioned. In other words, in bright conditions it's better to stop down the aperture rather than using a shutter speed that requires FP Flash.

Part 1
Part 2
Part 3

Mark

©Photosical - the photographic and philosophical observations of Orange County Photographer, Mark Jordan

Mark Jordan Photography
Orange County Family Portrait
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Orange County Photographer, Mark Jordan Photography, an Rancho Santa Margarita Photographer, specializes in crafting stunning contemporary, traditional, classic, and storytelling family portraits (high school seniors, children portraits, babies, maternity, pregnancy), headshots and pets. Mark Jordan, a Photography Hall of Fame photographer (with a Rancho Santa Margarita portrait studio), and provides portrait photography throughout Orange County and Southern California. Mark Jordan's Orange County portrait studio also serves San Diego County and Inland Empire. Studio Photography Services are also provided in Riverside County and Los Angeles County. Local Cites where Mark Jordan photography studio services are offered are as an Aliso Viejo Photographer, Anaheim Photographer, Costa Mesa Photographer, Coto de Caza Photographer, Dana Point Photographer, Dove Canyon Photographer, Huntington Beach Photographer, Irvine Photographer, Ladera Ranch Photographer, Laguna Beach Photographer, Laguna Hills Photographer, Laguna Niguel Photographer, Lake Forest Photographer, Mission Viejo Photographer, Newport Beach Photographer, Northwood Photographer, Orange Photographer, Orange Park Acres Photographer, San Clemente Photographer, San Juan Capistrano Photographer, Santa Ana Photographer, Tustin Photographer, Villa Park Photographer, Westminster Photographer, Yorba Linda Photographer, Corona del Mar Photographer, Riverside Photographer, Temecula Photographer, Chino Hills Photographer, Loma Linda Photographer, Rancho Bernardo Photographer, Carlsbad Photographer, Coronado Photographer, Del Mar Photographer, Escondido Photographer, San Diego Photographer, San Marcos Photographer, Solana Beach Photographer, Carmel Mountain Ranch Photographer, Rancho San Diego Photographer, Rancho Santa Fe Photographer, and San Diego Country Estates Photographer, Turtle Rock Photographer, Shady Canyon Photographer. Portrait Photographers everywhere (photographers in O.C. as well) are welcome to contact our portrait studio for mentoring/guidance.

Wednesday

FLASH PHOTOGRAPHY 101 - A BEGINNER’S GUIDE • 3 of 4

580EX Speedlite by Canon

A SYSTEMATIC APPROACH TO BOUNCED FLASH

Continuing with our four part series by Canon Forums, today we will be discussing the technique of "bouncing flash." While flash photography is complex enough that no single strategy works in every situation, the following approach has worked well for Mark Jordan Photography for over 31 year, and will work for you as well. We do make the assumption that you'll be bouncing you flash under fairly normal conditions, which we understand to be relatively small rooms (with typical low, white ceilings) such as is found in home settings, classrooms and offices.

Why Use Flash?
Simply put, adding light to indoor settings will allow you to use a faster shutter speed (less motion blur), a smaller aperture (more depth-of-field), and a lower ISO setting (less digital noise) than you could use with ambient light only. The focus-assist light on your flash unit will also help with focusing when needed.

Why Bounce the Flash?

We are accustomed to overhead lighting, so the shadows produced by light bouncing down from the ceiling will seem more natural looking. When the light from the flash hits the ceiling, it reflects down in all directions, illuminating the entire room. This creates a larger effective light source and produces more even lighting, softer shadows, and brighter backgrounds. When properly used, bounced flash will help to create images that don’t look “flashed” at all. Finally, bouncing will eliminate the redeye problems associated with direct flash.

Color Temperature Issues
Flash units produce a color temperature that resembles daylight. Incandescent (tungsten) lights have a much lower color temperature, and fluorescent lights have a higher color temperature along with other issues. Since most flash units have enough power to completely illuminate small rooms, my general recommendation is to reduce the amount of ambient light as much as possible by setting the shutter at flash sync speed (1/200 or 1/250 on today’s Canon DSLRs). This will make your flash the only significant light source, eliminating the problems caused by having multiple light sources at varying color temperatures.

Aperture Setting
You want an aperture setting that gives you sufficient depth-of-field, but don’t go overboard here. Smaller apertures (higher f/ numbers) will require a higher ISO setting to get sufficient illumination. DOF is a fairly complex concept, but generally speaking for indoor shots of people, f/4 should be enough for a single subject, and f/8 should work for most small groups. These are very general guidelines and the “best” aperture setting depends largely on your artistic goals.

ISO Setting
Now that we have the shutter speed and aperture determined, ISO is the last part of the equation to figure out. Since higher ISO settings tend to produce more digital noise, the trick is to set it high enough to get sufficient light without going higher than necessary. This sometimes requires a bit of trial-and-error, but ISO 400 is usually a good starting point.

Test - Chimp - Adjust
It’s often difficult to predict what aperture and ISO settings will be required to get proper illumination with bounced flash, so testing is always a good idea. With your camera in “M” mode and set according to the instructions above, and the flash unit in E-TTL mode, take a few shots of someone on the other end of the room. Immediately after each shot, look for the flash exposure confirmation lamp (FCL), near the pilot light on the back of the flash unit (on Sigma units, the “ETTL” indicator on the LCD will blink for 5 seconds). This indicates that the flash had enough power to create what it “thinks” is a correct exposure.

If the FCL doesn’t light, it means it didn’t have enough power for proper exposure with the settings you chose. You need either a wider aperture (lower f/ number) or a higher ISO setting. Adjust accordingly and test again.

If the FCL lights, take a look at your histogram to determine if the shot is properly exposed. If the image is too dark, dial in some +FEC (flash exposure compensation). The need for +FEC is normal with bounced flash and E-TTL flash metering. After adjusting the FEC, test, chimp, and adjust again as needed. More info on how to read a histogram here.

Once you have made these adjustments, you should be ready to make properly exposed images with bounced flash. But remember to check your FCL and histogram often! Many factors, including white clothing, windows, and changing backgrounds can “fool” the flash metering and require adjustments as you go.

Below is my usual configuration for bounced flash. Here are a few other points to remember.

Point the flash straight at whatever you want to bounce off. That means straight up for ceiling bounce. Avoid the 45 degree angle technique. This will tend to light only part of your subject directly and create the "hot spot" on the ceiling directly above your subject. Light from directly above is rarely flattering.
A 3 x 5 index card attached to your flash head as shown will create catchlights in eyes and provide a bit of direct illumination to fill in shadows.
Zooming the flash head to its widest setting will illuminate a larger area of the ceiling (creating a larger effective light source) and throw more light on the card.
Ceilings aren't the only surfaces you can bounce off of. A light colored wall beside or behind you can work too!

Part 1

Part 2
Part 4

Mark

©Photosical - the photographic and philosophical observations of Orange County Photographer, Mark Jordan

Tuesday

FLASH PHOTOGRAPHY 101 - A BEGINNER’S GUIDE • 2 of 4

Canon Speediites

(WHY) SHOULD I GET A SPEEDLITE FOR MY CAMERA?

A BEGINNER’S GUIDE

Many cameras, including some fairly expensive DSLRs, have a built-in (pop-up) flash unit, as well as a hotshoe for an attached flash unit. Beginners often call us here at Mark Jordan Photography and ask why or if they should buy a separate flash attachment - our tutorial today is designed to specifically answer this question.

Please forgive me for not offering any photographic samples below. The Canon Forum I am adapting this from did not provide any examples, and as much as I would love to, I am exceedingly busy creating family portraits in Orange County and didn't want to allow my hectic schedule to postpone the posting of this important information of flash photography. With that said, we are ready to move ahead.

REASON #1: REDEYE

We’ve all seen pictures of people whose eyes have that diabolical red glow. It can ruin an otherwise very good shot. It is caused by light reflecting off the retina in the back of the eye. This phenomenon is worst when the subject’s pupils are dilated (indoors), and when there is a narrow angle between the light source (flash), eye, and lens. Geometrically, the two factors which affect this angle are the distance between the flash and the lens, and the distance between the camera and the subject’s eyes.

One way to avoid this problem is to move the flash further from the lens. The more distance there is between the flash and the lens, the further away the camera can be from human subjects without causing red eyes. Typically, a hotshoe-mounted flash unit will be twice as far from the lens as a “pop-up” unit. A flash bracket can be utilized to make this distance even greater.

REASON #2: POWER

The effective distance of any flash is dependent upon the aperture and ISO setting used. For example, at f/8 and ISO 100, the built-in flash on today’s DSLRs will be effective only if your subject is within about 5 feet of the camera. Of course, you can increase this range by opening up the lens and/or using a higher ISO setting, but that comes at a cost - less depth-of-field and more digital noise.

A good flash unit has about fifteen times the power of a built-in unit, with perhaps four times the effective distance. This allows the use of smaller apertures (for better depth-of-field) and lower ISO settings (to reduce digital noise). Power is also critical for bounced flash and fill flash in sunny conditions.

REASON #3: BOUNCED FLASH

The ability to point the flash at a wall or ceiling will do more for the quality of flash photographs than just about anything else. It can mean the difference between a harsh-looking “snapshot” and a pleasing photograph that doesn’t even look “flashed”. Illuminating the ceiling has the effect of making the light source much larger, creating softer shadows, a brighter background, and more natural-looking results.

The power required for this technique varies widely according to the height and color of the ceiling and other factors, but even with a low, white ceiling it can require as much as four times the power of direct flash. With direct flash, you’re lighting up your subject. With bounced flash, you’re lighting up the whole room!

REASON #4: FLASH MODIFIERS

There are a wide range of “diffusers” and other attachments which somehow modify the direction of some or all of the photons flying out of the flash unit. They can be as simple as a 3 x 5 index card and rubber band.

Other attachments include the Lumiquest Promax System, mini softboxes, the Sto-Fen Omni-bounce, and the Lightsphere II. They all work a little differently and they each have their place. Generally they are designed to make the light source larger from the subject’s perspective, or to provide some direct illumination with bounced flash.

Another completely different modifier is the Better Beamer, which creates a powerful, narrow beam for long-distance wildlife shooting. When used properly, flash modifiers can dramatically improve flash photographs, but you need a flash unit to use them.

REASON #5: FLASH BRACKETS

Flash brackets come in a variety of styles and serve a dual purpose. In addition to moving the flash unit further from the lens (see reason #1), they also allow the camera to be rotated to vertical orientation while keeping the flash above the lens. This prevents those ugly side shadows on backgrounds which otherwise ruin vertical shots when using a hotshoe-mounted flash indoors.

Some styles work by flipping the flash unit, keeping it oriented the same way as the camera. These allow the flash to be zoomed with the lens to avoid wasting light (and power) with direct flash.

Other styles allow the camera to rotate while the flash remains over the camera. These make it easier to change orientation while mounted on a tripod, and they work better with some flash modifiers such as the Lumiquest Promax System. Use of a flash bracket requires a sync cord to electrically connect the flash to the camera.

REASON #6: BELLS and WHISTLES

Most good flash units have additional features not available with the built-in. They include:

a focus assist light - This light casts a pattern of lines on your subject to allow the autofocus system to work better in low light situations.
FP Flash (high speed sync) – This enables the use of high shutter speeds. If you’re using fill flash outdoors and want to use a wide aperture to blur the background, FP Flash is a necessity.
manual mode – This allows you to set and adjust the flash unit’s power, rather than relying on automatic flash metering, and also enables the use of optical slaves. It’s more of an advanced option, but sooner or later you’ll find it useful.
wireless E-TTL – Allows the use of multiple flash units at various power ratios in a master/slave arrangement with E-TTL flash metering.

To summarize, today’s Digital SLRs are packed with amazing technology, and with the right lenses they can produce wonderful images. But the built-in flash units on these cameras are lacking in power, too close to the lens, can’t be tilted for bounce flash and can’t be used with flash modifiers. In short, they rarely produce anything better than “snapshot” quality. Their usefulness is so limited that high-end professional camera bodies don’t even have a built-in flash.

My recommendation to people who buy a DSLR is to buy a good flash unit for it as soon as funds allow. While there are many types of photography that don’t require flash, most beginners photograph people more than any other subject. Flash can improve just about any “people” shot, whether indoors or outdoors. Before you buy another lens, before you get that fancy tripod or any other accessory, buy a great speedlite!

Not sure which one to buy? Take a look at Tim's thread: Which flash should I get for my EOS camera?

Part 1

Part 3

Part 4

Mark

Monday

FLASH PHOTOGRAPHY 101 - A BEGINNER’S GUIDE • 1 of 4

580EX "Speedlite" by Canon

FLASH PHOTOGRAPHY 101

A BEGINNER’S GUIDE

INTRODUCTION

At Mark Jordan Photography, we primarily employ Speedlites as a "fill light" while allowing the ambiant light to capture your family portrait. Our portraits use just enough fill to add a touch of sparkle to the eyes and teeth, as well as lighten the depth of shadow. Should you like to see examples of our Orange County family portraits, drop by our website, Mark Jordan Photography, take a look around and contact us if you like.

Though there are thousands of photographers in Orange County, Mark Jordan Photography has been specializing in family portraits, headshots, senior portraits and children since 1981 - we are more enthused today than when we first begun. The new Speedlites have have been a godsend, and are instrumental to our success in family photography.

FLASH PHOTOGRAPHY IS EASY ONCE YOUR UP TO SPEED
If you find using flash to be a frustrating experience, have no fears. For most beginning photographers, mastering flash photography is considerably more complicated than ambient light photography. However, when you come to understand the intricacies of Speedlites and what occurs during flash (just a few milliseconds after you press the shutter button), you'll be well on your way to taking consistent flash photographs, AND with predictable results.

Before we begin, you should be aware that just about all the information provided below, as well as in the following three parts, is thoroughly covered in The EOS Flash Bible. The EOS Flash Bible document, however, is both comprehensive and long. Thus, I thought this short guide might not only be more beneficial but serve you down the road as a reference source.

Now then, let's begin.

THE BASICS
Before you venture into the world of flash photography you first need to understand the basics of exposure. Our guide makes the assumption that you're knowledgable of how shutter speed affects exposure and crispness/motion blur, how aperture affects exposure and depth-of-field, and how the ISO setting affects exposure and digital noise. If you not yet up to speed and possess a working grasp of these essential concepts, you would do best to put aside this guide for a spell, and first master the basics of your camera before venturing off into the depths of flash photography.

PART 1

FACTS THAT EVERY FLASH SHOOTER MUST UNDERSTAND

Whether you’re using the camera’s built-in flash, a hotshoe-mounted flash unit, or studio strobes, the first four facts are universal and pertinent to all of them.

Flash Fact 1

Every flash photograph is two exposures in one – an ambient light exposure and a flash exposure. This is a critical fact to remember. The shutter opens, the flash fires, the shutter closes. During this time, both ambient light and flash will contribute to the recorded image. Flash photography requires managing both exposures.

Flash Fact 2*
Flash exposure is not affected by shutter speed. The entire burst of light from the flash begins and ends while the shutter is open, so keeping the shutter open longer won’t help with flash illumination. The flash exposure and the effective range of your flash unit will be affected by aperture and ISO settings, but not the shutter. Of course, the ambient light component in a flash photograph is affected by shutter speed. So changing the shutter speed is one way to manage the amount of ambient light that contributes to a flash photograph.

Flash Fact 3
Flash illumination is dramatically affected by distance. This is known as the inverse square law. Think of it this way: Suppose you’re using a lens that gives you a 4 x 6 ft. field of view at a distance of 10 feet. That same lens will give an 8 x 12 ft. field of view at a distance of 20 feet.

So when you double the distance, the same light is covering an area four times larger (96 square feet vs. 24 square feet)! So you need four times as much light to get the same illumination. This phenomenon, sometimes referred to as flash falloff, will affect any image with more than one subject at different distances.

Whenever your subject distance increases by a factor of roughly 1.4 (the square root of 2), the flash illumination will be cut in half. Suppose you’re taking a large group portrait. The people in the first row are 10 feet away, and the people in the back row are 14 feet away. With on-camera flash as the primary light source, the front row will be a full stop brighter than the back row!

In the image below, each cup is one stop brighter than the one behind it, and one stop darker than the one in front of it. It would take 16 times as much light to properly expose the cup at 11 feet verses the cup at 2.8 feet. Do those distance numbers look familar? They're the same as standard f/ stops for aperture settings, and the relationship is identical. This thread from PhotosGuy gives an example of how to use this relationship in the field.

Photo Courtesy of PhotosGuy

Flash Fact 4
Your camera measures ambient light and flash illumination separately. In Av, Tv or P modes, it will attempt to expose properly for the ambient light by adjusting either the shutter speed, aperture, or both. The fact that you have your flash turned on has no effect on this** ( one exception is that in P mode it will not use a shutter speed slower than 1/60 with flash). The camera’s metering system cannot predict how much illumination will be gained by the flash, so it doesn’t try. In manual mode, the meter in the viewfinder measures only ambient light, because that’s all it has to measure.
Fact 5 refers to any form of automatic flash metering, including older “auto thyristor” flash units, TTL film cameras, and E-TTL or E-TTL II digital cameras.

Flash Fact 5
With automatic flash metering, the flash illumination is measured after the shutter button is pressed, and the flash output is adjusted accordingly. There are technical differences between the various types of flash metering, but all of them operate independently from the camera’s metering of ambient light, and all of them work by adjusting the output of the flash, not by changing the camera’s exposure settings.

Facts 6 and 7 apply to any camera with a focal plane shutter (all SLR cameras with a mechanical shutter).

Flash Fact 6*
Every SLR camera with a mechanical shutter has a maximum flash sync shutter speed (1/200 or 1/250 on current Canon DSLRs). This has to do with the way focal plane shutters work. At slower shutter speeds, the first curtain opens, the flash fires, and after the specified time duration, the second curtain closes behind it. At shutter speeds faster than flash sync, the second curtain begins to close before the first curtain is completely open. The second curtain follows the first across the frame, exposing only a slice of the image at any given moment. Firing a flash during this process would illuminate only part of the image.

Flash Fact 7* [Applicable to modern electronic cameras only]
If you set your shutter speed faster than flash sync, or use Av mode with an aperture setting that requires a shutter speed faster than flash sync for proper exposure, the camera will automatically revert to flash sync speed when the shot is taken if a built-in or hotshoe-mounted flash is turned on. Usually this results in overexposure (unless you have a “safety shift” custom function enabled). If you’re getting overexposed images when using flash outdoors, this is probably the reason. The image is not overexposed because of light from the flash. It’s overexposed from ambient light because the shutter speed was too slow. If you’re using flash for fill in bright situations, it’s necessary to stop down the aperture or lower the ISO setting to get the shutter speed below flash sync.

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* The exception to facts 2, 6 and 7 is FP Flash, sometimes referred to as “high-speed sync.” That topic is covered in Part 4.

**With some Canon cameras there is a poorly-documented phenomenon called NEVEC (negative evaluative exposure compensation) which will adjust the ambient exposure by up to a full stop when the flash is turned on, but that’s also a topic for another chapter.

Part 2
Part 3
Part 4

Mark