What is “Exposure Bracketing”

The word “bracketing” is a military term that dates back to artillery units firing at a distant target.  If they zeroed in on a single distance, any error would make each shot a miss.  If they instead “bracketed” their target by shooting within a range of distances, some would be long and some short, but some would be right on target.

Many cameras are equipped to “exposure-bracket” automatically (AEB).  The images above show a bracketed set:  The top picture is the camera’s attempt to get the shot right in one shot.  Then next one is the same scene that’s 1 stop darker, and the last is 1 stop brighter than the first one.   In this sequence, notice the bright “highlight” areas (eg. the computer screen) and the dark “shadow” areas (eg. the man’s hand on the keyboard).  Picture number 2 has the best screen, and picture #3 has the best hand.  Now watch as the three shots are blended together in a photo-editing program:Blending is only one advantage of exposure-bracketing.  Even if you’re not an editor, it can be a great safety net to be sure that at least one of your shots has the right exposure.  A tripod is essential when shooting brackets for blending.

Author’s note:  Today most of my paid shooting is for product photography.  Because my subjects are never moving, I shoot from a tripod and exposure bracket almost 100% of my shots.  I’m in aperture priority with the ISO set at 100 (for noise-free shots), leaving the shutter to do all the exposure adjustments.  Without this procedure, I’d take down my 585photo.com website immeditately.

What is a Camera “Stop”?

what is a stop?

A stop in cameras is a doubling or cutting in half of light.  Using money as an analogy, if I start with a dollar and my money increases by one stop, I now have two dollars.  If I start with a dollar and it increases by two stops, I now have four dollars (not three).  If I start with a dollar and it goes up by three stops, I now have eight dollars: One becomes two, two becomes four, four becomes eight.  Reverse that when decreasing.

Cameras have three light-management tools:  Shutter, aperture and ISO.  Each is measured in different terms.  Shutter is measured in seconds and fractions of a second.  Aperture is measured in “f-number” or “f-stops”, which is the ratio of the focal-length to the diameter of the opening inside the lens (aperture).  ISO (aka “film speed” for film) is measured in a scale commonly starting with a low of 100 through a high of 1600 to 12800 or higher.

Imagine the time before airliners could fly around the world.  American pilots spoke English to American control towers, but what about those first flights to French or Spanish-speaking destinations?  Today of course the airline industry requires that all pilots and control tower personnel be fluent in English, because English was declared the official language of the international air traffic industry.

Now imagine the days before digital photography and preview screens that let us “dial in” our settings by trial and error.  Photographers had to calculate their settings before the shot, and then wait until the prints came back from the developer to find out how they did.  What was needed was a common “language” that put all three controls on equal footing.  That language was “stops”.

Let’s say that a film photographer knows that his settings are right for the conditions:   If he then increases his shutter speed by one stop to avoid motion blurring, the picture will be darkened by one stop.  He then can either use film that ‘s one stop faster, or increase his aperture by one stop.  Either one will offset his shutter adjustment, and keep his original exposure correct.   Of course the same is true for a digital photographer, except that instead of switching films, that part of the process is now a control on our cameras just as shutter and aperture are.  In fact, you may have noticed that when you spin the dial that adjusts each of these three settings, you feel it clicking.  Each of these clicks represents an adjustment of either 1/3 or 1/2 stop either way (see your manual for more).

How to Blur Backgrounds

Learning how to blur backgrounds is better said:  Learning how to manage my “DOF – Depth of Field”.

Have a look at the picture of the text above.  This image has a very shallow depth of field because only one line of text is in focus.  There are three factors that contribute to this effect, and it’s important to know each one.

  1.  Aperture – Recall that aperture is one of the three light management devices in our cameras, and that it refers to the adjustable opening inside our lenses.  The size of the opening is expressed as “f-stop”, and the numbers start from a low of 1.8 and rise to usually about 22.  The important thing to know and remember about these f-stop numbers for this tutorial is that the lower the numbers, the wider the opening, and the shallower the depth of field (hence the greater the amount of blurring both before and after the DOF).
  2. Lens Length – Lens length is expressed in millimeters, and is the way magnification is expressed in camera lenses.  The rule to know in the context of blurring backgrounds is that the longer the lens, the shallower the DOF and the greater the amount of background blurring.  Note that when we say lens length, we’re not talking about how long the actual lens body is, but how many millimeters of length has been designed into the lens.  That is, the effective length of a zoom lens for instance, is the number you have the lens set to, not how long the lens actually is.
  3. Focus distance – Finally, the farther you are away from your subject when you zoom in on it, the greater the DOF compression, and therefore the greater the blurring effect you’ll realize.  This is often convenient, as the farther away you are, the more you’re likely to zoom your lens to magnify the subject, and together they’re working toward the same end.

The bottom line then is, for the greatest DOF compression and the greatest background blurring, Choose the lowest aperture number, and the longest lens, at the greatest distance practical.

Parenthetically, often new camera owners are disappointed to find that they’re not able to blur backgrounds at all.  Most kits include a very short zoom lens that tops at 55mm.  Can you see what their problem is?

How to Photograph Moving Water

Learning how to photograph moving water involves a study of your camera’s shutter speed.  Let’s slow this tutorial down to the speed of the slowest walker for a minute:

Your camera’s shutter is one of the three “light management controls”.  It’s the faucet in our “How Do Cameras Work” session.  When the shutter opens, light flows into the camera.  It continues to flow until the shutter closes again.  The shutter’s “speed” is measured by the time it remains open.  In the pictures above, the shutter speed in the right picture is 1/125 of a second.  The shutter speed in the left picture is expressed as the decimal .4, or 4/10 of a second.  1/125 of a second is less time than 4/10 of a second, so the one on the right is said to have a faster, or a higher shutter speed.  Sometimes people are confused by that because they think that increasing the shutter speed means more light comes in, but it’s the other way around.

Think of shutter speed as “cutting a slice of time” with your camera.  In the picture above, the slice of time on the left is thicker than the one on the right, and the water was able to move more during that slice than the thinner slice on the right.

Don’t be discouraged if math isn’t your subject and you find these numbers hard to work with.  Consider keeping a list of “recipes” for various shooting situations with you when you go shooting.

While we’re here, notice that the brown wall on the very right edge of both of these images is exactly the same in both.  That means that the exposures are the same, which means that when we changed the shutter speed to get the two effects, one or both of the other two light controls (aperture or ISO) had to move in the opposite way (let in more or less light accordingly) to keep the exposure the same.

How to Photograph Blue Skies

You may already know how to photograph blue skies, but for everyone else, let’s see what these two shots can teach us:

Both images were taken of the same scene only a few minutes apart, and both are facing in exactly the same direction (north).  Notice the exposure and color of the dancers in both shots.  That shows that the skies in both images should also be identical, but they’re not.  The sky on the right is clearly superior.  The question is, how did that happen?  Here’s a hint:  There were NO settings changes whatever between those two photos, and nothing was done in post-production.

Did you notice that the shot on the left is vertical (portrait) and the one on the right is horizontal (landscape)?  That’s the reason the skies in these photos are so different.  What could explain that?  The camera was equipped with a polarizer filter that day.   Polarizers are used to accomplish two effects in our images:  One is to reduce glare from reflective surfaces, and the other is to allow blue light from the sky to pass through to our camera’s sensor, as in the shot on the right above.

Polarizer filters are characterized by having two filters connected together in such a way that you can turn them with your fingers and they remain joined together.  They do that because polarizers work their magic only if the filter is turned to a certain point relative to the direction of the sun.  I turned the filter until the sky was dark blue in the shot on the right, then forgot to re-adjust it when I turned the camera to vertical for the second shot on the left.

Portrait, Landscape… and Sabrina

In the movie Sabrina, there’s a scene where Sabrina (played by Julia Ormond) is photographing a property for her employer.  Her character had learned to use a camera from fashion photographers in Paris, and when she spotted a lighthouse in the distance, she lifted the camera to frame the shot horizontally.  As soon as the shutter released, she smoothly turned the camera ninety degrees to get the same shot vertically as well.  I smiled when I saw that, and wondered if Julia Ormond was that good a photographer, or was the gesture written into the script for her.  Maybe it was director Sydney Pollack’s suggestion, or even a tip from one of the cameramen on the set that day.  However it happened, it showed that Ms Ormond’s character Sabrina knew what she was doing.

The best way to learn how to shoot video is to spend time in front of an editing program turning footage into a finished story.  The same can be said for still images.   Who knows how an image will be used on a website, in print, or framed and hanging behind a couch?  Will the editor have to fill a vertical space, or will the image be used full width as a header or footer?  Finish editors appreciate having as many choices as possible, and when shots matter, as for a wedding or commercial shoot, you’ll be glad to follow Sabrina’s example by always thinking to get both landscape and portrait versions of each important shot.

Why Aren’t My Pictures Sharp?

The three light management controls in our cameras are shutter, aperture and ISO.  Each has a secondary, or “side” effect that relates to sharpness in our pictures.  Understanding what those side effects are, and learning to detect which is causing the blurring in our images is the first step to getting sharp pictures in the first place.

Motion blurring is the result of movement of either the subject, or the camera, or both while the shutter is open.  If the shutter is open for a short time, the blurring is less. If it’s open a long time, the blurring is greater.   Think of shutter speed as cutting “slices of time”.   The thinner the slice, the less motion blurring you’ll see in your image.  Motion blurring can easily be confused with Focus blurring, except that motion blurring usually has a direction (imagine the camera moving from left to right or up and down).   Also, blurring due to camera movement should affect every pixel in the image the same, wheras focus blurring often affects only part of the picture.

Focus Blurring sometimes happens just because we fail to focus properly berfore taking the shot.  Focus blurring can also be the result of a shallow “Depth Of Field”.  Certain combinations of lens length, distance from the subject and wide aperture settings can create blurring in the foreground and background.

Noise is sometimes mistaken for blurring, but really it’s a pebbly distortion that’s associated with high ISO settings.  Because higher ISO’s are used to get better exposures in low-light situations, shots after dark or in dimly lit rooms tend to be noisy.  Interestingly, noise in film cameras happens because of a chemical reaction in the film.  Noise in digital cameras happens because of electronic static from solar winds (the ISO adjustment is really just an amplifier, not unlike a volume control in radios).  Despite this difference between film and digital, noise looks almost exactly the same in both film and digital finished images.


Should I Buy a Tripod?

Tripods are devices used to hold cameras still. If a camera moves when the shutter is open, there will be a certain amount of “motion-blurring”. The longer the shutter is open, the greater the blurring. If a shutter opens and closes quickly enough, then the blurring will be so small as to be not an issue at all.

You may or may not believe that Pablo Picasso was a great artist.  I didn’t think so myself until I learned that when he was a little boy he could paint the feet of pigeons better than his art-teacher father could.

You’ll read camera book authors who will tell you that their images have “soft focus”.  My cynical instincts always rise up when I hear that. “Soft focus” can be a euphymism for “I failed to get a sharp capture”, and I warn you to not fall into that trap yourself. Picasso had already proven that he knew how to draw what he saw before going abstract.  Before you pass your blurred images off as “artistic”, first be very sure that you know how to get “tack sharp” images in the first place every time.  Tripods are the first step toward sharpness for any photographer, no matter what they say about how still they can hold a camera without one.

It’s true that shutter speed can reduce or even eliminate motion blurring, and you should memorize and apply the rule for that every time you have to shoot without a tripod. We’ll talk about this again in another session, but here it is:

When shooting handheld, your MINIMUM shutter speed should be the reciprocal of your lens length, but in no case slower than 1/100th of a second. A reciprocal is the fraction formed when you put a 1 over the /…. so if you’re shooting through a 300mm lens, your minimum shutter speed should be 1/300th of a second.

See also The Illusion of Sharpness

How to Use The Mode Dial

The first question any new camera owner should ask is, “how to use the mode dial”.

This is important:   You and your camera are partners in this process of creating good photographs.  The camera can’t think for itself, but it can make an amazing number of decisions without you if you need it.  The mode dial is where you tell the camera what your level of skill is, and therefore how many decisions you expect it to make in the shots you’re about to take together.  Got it?  Alright, now look at the picture above:

AUTOMATIC vs CREATIVE – We’re going to divide that dial into two parts:  The AUTOMATIC settings, and the CREATIVE settings (sometimes called “manual” settings, though that can be misleading).  The creative settings are the letters P, A, S and M on the right side of the dial.  They’re for photographers who have built some level of skill.  We’ll spend lots of time talking about those, but not just now.  The “MR” near the bottom of the dial isn’t important, so skip that.  The settings on the left (from 7:00 to 1:00 if this was a clock face) are the automatic settings.  These settings give almost total control to the camera, and are where beginners will have the best success.

Automatic vs FULL Automatic – The tiny icons are meant to describe shooting circumstances that — if you choose the right one — will tell the camera to make decisions for slightly better pictures.   For example, see the image on the dial above that looks like a runner in a race (at 9:00)?   You can choose that if you expect fast action where increased shutter speeds will help to prevent motion blurring.  Check your user manual for what the others mean.  The “AUTO” setting at 1:00 with the green background is full automatic, where you’re telling the camera that you don’t even want to make those decisions.

BUT MOST OF ALL – We’ve divided the mode dial into two parts.  Now divide all of your shooting into two kinds:  Shots that matter, and those that don’t.  Shots that matter are kids birthday parties.  Aunt Edna’s trip to Niagara Falls.  The new baby at the hospital.  Shots that don’t matter are the squirrel in your back yard.  Pretty leaves on your maple tree.  When shooting shots that matter, set your camera in the setting where you feel most confident, given your skill level .  But when shooting shots that don’t matter, get over into a setting that you haven’t learned yet, and practice to grow that particular skill.  Do NOT practice blurring backgrounds at your sister’s wedding!   Also for you experience readers, there’s no sin in shifting to full automatic when the father and bride start down the aisle.

How Do Cameras Work?

We did a presentation to a local photo group a few years ago, during which I used the photo you see above to illustrate how cameras get correct exposures. After the meeting a woman in her young thirties told me that she’d built a successful wedding photography business already, but that it wasn’t until she saw that picture that she understood how shutter, aperture and ISO related to each other.

It’s an analogy of course: The water represents light flowing through the camera’s lense. The glass is the camera’s sensor, and the object is to just fill the glass. If it’s not full the image is underexposed. If it overflows like this one, the image is overexposed. The three variables in this picture are the faucet that turns the flow on and off, the size of the pipe (diameter, not length), and the size of the glass.

Water begins to flow when the faucet is opened, not unlike light flowing into the camera when the shutter opens. It continues to flow until the shutter is closed. When open, the amount of light getting through to the sensor depends on the size of the opening. In cameras, that opening is variable, and it’s called the aperture. Finally, the size of the glass works a bit like ISO. ISO describes how sensitive the sensor is to light. When the ISO is very low, the sensor is slow to respond, and it takes more light to “fill it up”… like a large glass, you might say. So the way to think of it is that the shutter and the aperture both control how much light flows to the sensor, while the ISO setting on the camera controls how much light is NEEDED to get a good exposure.

We’ll spend quite a lot of time learning more about those three controls later, but if you’re new to this, it might make sense to spend some time digesting this image for now.