The Mystery of Exposure - Part 1

Ah...exposure.  That dreaded word that novice and experienced photographers alike hate.  Well, contrary to popular belief, the principles of exposure are really not all that complicated.  It just takes a basic understanding of what is involved.  Exposure is a process of three separate but related functions.

            1. The mechanics / functions of the camera
            2.  How the camera functions relate to each other
            3.  How to use that knowledge when taking a photograph

Blog space does not allow for an in depth description of these elements, but what I'd like to do is break it into three parts and briefly discuss each.  With any luck at all, I hope to clear up some of the mystery and maybe get you to thinking differently about what you're doing when it comes to taking a picture.

Let's begin with the mechanics.  Exposure is made up of four things...or the Exposure Triangle:
                         ISO
                 White Balance
             Aperture  /  Shutter
            
Some people think that white balance is separate, but for arguments sake, I'm going to include it in the discussion because it does affect the visual outcome of the image.

Aperture:  The aperture is what regulates how much light enters the camera. It is a function of the lens. Think of it like using a faucet to fill a glass with water.  Turn the faucet to where a trickle of water comes out and it takes a long time to fill up a glass. Turn it wide open and the glass fills up quickly.  The same thing applies to the lens aperture and exposure.  Allow in just a trickle of light and the exposure process takes longer.  Allow in a lot of light, and the exposure takes less time.  It's really that simple.  But you may be wondering about all those numbers on the lens or the ones that keep flashing on the camera's display.  An aperture is designated in what are call  f/stops...F followed by a number like 16 or f/16.  F stops are actually calculated using a mathematical progression based on a factor of 2...but you don't need to worry about that. All you really need to know is that the larger the f/stop number, the smaller the actual lens opening.  The smaller the f/stop number, the larger the actual lens opening.

Take a number like f/16 or f/22.  These are large f/stop numbers but they represent a rather small aperture setting and allow in a small amount of light.  A number like f/2.8 or f/3.5 are small f/stop numbers, but they represent a large aperture and allow in a large amount of light.

Aperture is also a factor in what is called Depth of Field or DOF.  I'll talk more about that in part 2, but basically DOF is what portion of the image remains in focus from foreground to background.

Shutter:  The shutter is an electro-mechanical devise that regulates the length of time the light is allowed to enter the camera.  It is usually represented in some fraction of a second such as 1/10th of a second or 1/125th of a second.  The shutter and aperture work together to generate the mechanical exposure process.  Pretty straight forward.

ISO:  Understanding ISO is actually quite simple, it's understanding how it affects the combination of aperture/shutter sequence that is confusing (more on this later).  ISO is simply the sensitivity to light setting that your digital camera's sensor is set to...or how sensitive the film is to light if you are using film.  ISO usually begins at 100, but can go lower...and then it progresses upward doubling in sensitivity as you go up the scale.  So, ISO 200 is twice as sensitive as 100.  ISO 400 is four times a sensitive as 100...and so on.

White Balance:  Different kinds of light have different properties and light temperature is defined using a temperature scale called the Kelvin scale.  On the Kelvin scale, very cool light, like cloudy skies, or twilight skies has a very high Kelvin temperature, as high as 10,000 degrees Kelvin. Very warm light has a low Kelvin temperature...down around 1800 or so...kind of opposite of what you might think.  The source of the light also affects the Kelvin temperature.  Candle light is very warm and reddish in nature as is indoor light from a tungsten light bulb. Light from those kinds of sources have very low Kelvin temperatures...like 1800  to 2000 or lower. Middle of the day, blue sky light has a temperature of around 5500 Kelvin.  Outdoor light is different than indoor light and the digital camera must be able to distinguish between the two or your images will not look normal...they could be too blue or too red.

Okay...we've briefly defined all the elements of the exposure triangle.  Next time, we'll talk about how the elements of the exposure triangle interact with each other.  You don't want to miss that part as that is when I get into the nitty gritty of how the camera does what it does.

Keith

The Prairie Storm

It always amazes me how photography is so sensitive to time…a matter of a few minutes and in some cases a few seconds can make the difference between getting the shot or missing it. That’s what happened to me one morning. I left Tulsa at 4:45 am so I could be on location at the Tallgrass Prairie by sunup. The sky was broken and as I got closer to the preserve it started to look like it was going to be a spectacular morning. It was…unfortunately I was about 15 minutes too late to capture the best of it…at least at the location I wanted to capture it. I did manage to snap a couple quick shots before I lost the moment…but I had to rush and shoot by hand…not sure what the images will look like.

When I finally arrived at my favorite morning location, the best of the morning show was beginning to wind down…I did get a few shots…but bit my lip all morning knowing that if I had only left a few minutes earlier I would have caught one of those perfect lavender mornings on the prairie.

Within minutes after I arrived…it clouded over. Within an hour it began to rain…a few minutes later a classic prairie storm blew in…thunder, lightning, and torential rains…it was fun to experience. The once bright morning sky grew almost black within seconds…just before the main rain event erupted…Man what a treat!

Prairie storms in Oklahoma are an amazing event to experience...especially when you are caught out in it. On a previous trip up there I managed to arrive just as one storm was finishing. During the drive up there the pre-dawn light was lit up by dozens of lightning bolts exploding all around me. Right at first light most of the storm had passed on to the east so I hiked a few hundred yards to the top of rise so I could feel the wind and experience the remnants of it in person. It was amazing...it was also rather foolish. As I stood on top of that rise...exposed as I was...I realized I was the tallest object inside of 500 yards in either direction. Lightning was still flashing off in the distance, so I wasn't too concerned...until one bolt ripped the sky apart just a few hundred yards away. I jumped about six feet when the boom hit me. A short time later I retreated to the safety of my vehicle.

On another trip, I followed a particularly severe storm up there and arrived well before daylight.  By the time I arrived the rain had moved on to the east, but the wind was gusting upwards to about 40 mph.  Again, lightning was exploding all around.  I sat my camera on a tripod and positioned it on the lee side of my Jeep to block some of the wind.  Attached a wide angle lens and set the shutter release to Bulb which when used with a cable release, allows the shutter to remain open until you let go of the release button...then pointed it toward the most lightning activity.  Took several tries but managed to get one good shot of a flash across the prairie landscape.

Storms on the prairie are one of natures most exciting events to experience and can provide some of the most unique photo opportunities...but they can be dangerous and caution is the better part of valor in most cases.

Got any storm stories...loved to hear about them.

Keith Bridgman

In Need of an Adventure

I'm in desperate need of some kind of adventure.  Been way too long since I was able to get out and face some kind of outdoor challenge.  Other than an occasional day outing or maybe hiking across Oklahoma's Tallgrass Prairie on a photo safari, the last real adventure of any length I had was a multi day float / camp / fishing trip down Arkansas's Buffalo River about three years ago.  I love that place.  It's one of the few places in that area where you can experience a near wilderness adventure...at least for a few days anyway.

Arkansas's Buffalo River is one of the few rivers that remains intact from its source, the Boston Mountains in the Ozarks, to its end, the White River toward the north central part of the state.  Over one hundred and fifty miles of scenic splendor like 500 foot bluffs, clear water, magnificent night skies, wildlife, and heavily wooded Ozark country side   On the upper end you'll encounter faster moving currents and some pretty good rapids along the way especially if the river is running at optimal levels.  Over the course of its length, the river's personality changes and the current further down is characterized by slower moving currents and longer pools.

The fishing is usually pretty good with lots of smallmouth bass, Kentucky bass, and assorted other creek related swimming critters.  The closer you get to the White River, you might even tie into a rainbow trout as the White is one of the best trout fisheries in the country and they tend to migrate a few miles up the Buffalo.

Over the years, some of my hunting and fishing buddies and I have made numerous trips down the Buffalo.  We pack all our gear into our canoes...spot a vehicle at the takeout...and shove off.  Most of our trips run about three days or so, but we've made trips up to five days on the river.  It's a great adventure.

Sometimes the weather doesn't co-operate and we've been caught several times on the river during an Ozark thunderstorm and downpour.  Sure makes for an interesting adventure when that happens.  I've rarely been able to capture the Buffalo photographically at least in the way I know is possible.  Mostly because of time and weather not always coordinating with each other.  But, I never fail to at least make the attempt for there is no shortage of opportunity...it's just a matter of combining the opportunity with the right kind of light.

One of my favorite places on the river is the area called Skull Bluff.  Actually its an area that extends several miles upriver from Woolum, to Skull Bluff, to the Nar's.  The Nar's is a unique geological formation where two separate river systems, Richland Creek and the Buffalo, have eroded both sides of a ridge to where a narrow slit or wall of rock maybe 150 feet high separates the two sides.  If you're brave enough, you can climb up the ridge from down stream and work your way over to the narrow wall and walk out on to it.  I've done it a time or two, but will probably never do it again as I'm not as brave as I was in my younger years...or maybe I've gotten a bit wiser...in either case...I've had thrill enough of standing on that four foot wide ledge and seeing nothing but air straight to the bottom broken by a few tree limbs.  I did catch the largest smallmouth I've ever caught at the base of the Nar's.  A nice, deep, pool swirls around where the rock wall climbs skyward from the water, and grandaddy smallmouth bass tend to prowl around in its depths.

Of the friends I've floated the Buffalo with, two of them are gone now.  Although they are no longer able to make those floats, the memories of the times we had still pleasantly linger.  Those stories are told over and over again when the rest of us do manage to regroup, and share a few days of adventure...I think I'll give them a call soon and see what kind of adventure we can conjure up...like I said...It's been way to long.

(Would love hear about your adventures...)

Keith Bridgman