Have you ever taken a photo where your subject looks like a deer in the headlights from the flash while the ambiance in the scene behind them fades quickly to a black abyss?  Or, you try to catch your child scurrying around the house and no matter what you do, the picture turns out as a blurred mess?  This post is being written to help those (mainly my mom) who’ve asked me “how do you do that?” when they see a picture that avoids some of the common frustrating problems.  Whether it be a selective focus, blurred action to accentuate movement or an image that is intentionally over or underexposed, the key to photography is understanding the three main components of proper exposure control.  Hold on to your hat, I am going to help get you off of the ‘auto everything box’ and manipulating your own exposure in no time.

Firstly, let’s quickly discuss the whole purpose of a photographic capture device.  It could be an 8×10 view camera, a digital SLR, a pocket camera or a shoebox with a hole poked into it to expose a frame of film.  Photography is the capture and manipulation of light.  Plain and simple right?  Current camera technology is amazing.  There are cameras that will recognize your face and tag the image with your name now, all while doing a pretty good job of exposing for the scene before it and then wi-fi the image file to your computer.  The automation involved is nothing short of modern magic, but what happens when you want the control of whose face you want to focus on, or prefer to not have to restrain your child to capture the moment?  Auto exposure does a good job in most cases, but it has preset limitations to essentially use the lowest common denominator in its approach to exposing a scene, disallowing the photographer the ability to creatively control the elements of exposure.

I think of exposure as juggling.  In order to gain a proper exposure, you need to juggle three things, ISO, shutter speed and aperture.  All three of these are adjusted in “stops.”  Stops, in most modern cameras are adjustable in 1/2 stop or 1/3 stop increments.  For this, I will be listing everything in “full” stops for ease and due to general laziness on my part.  To adjust for proper exposure, if you adjust the aperture up by a stop, you will need to adjust either the ISO or shutter speed down by a stop to achieve the exact same exposure.  Here in lies the exposure juggling dance.  It may seem tricky, but bear with me, it really is simple plus cameras come with a light meter for a reason.  I tend to break exposure down into a mental checklist as I assess the scene I am shooting.  We will ignore metering, white balance and exposure compensation for now.  The first three steps in my mental checklist are as follows:

#1 – ISO

Some of you may remember going to the store to buy a 24 or 36 exposure roll of film.  If you knew you were going to be outside at the beach on a sunny day, you would get a roll of ISO/ASA 64 or 100 daylight balanced film right?  If you were going to be inside, you may opt for the “faster” 400 or 800 ISO tungsten/incandescent balanced film.  ISO, digitally speaking anyway, is merely an adjustment to compensate for different conditions based on light sensitivity.  The hard part in film days, was, once you were done at the beach and went back home to try and finish off your roll, everyone looked really orange and blurry due to the slow ISO and incorrect light temperature compared to the film’s original intended use.  The beauty of digital, is from one shot to the next you can adjust the ISO (and white balance/light temperature – we’ll get to this later) to help your exposure based on the amount of light you have to work with.  If you are outside on a nice sunny day, set it somewhere around ISO 100-200.  If you are at a candle lit restaurant, crank it up to ISO 1600 or higher.  Much like “fast” film, higher ISO settings digitally produce more grain, or in digital terms, “noise”.

ISO setting in full stops: 50 – 100 – 200 – 400 – 800 – 1600 – 3200 – 6400 – 12,800 – 25,600  – 51,200 – 102,400 – 204,800, etc

#2 – Aperture

An aperture is basically a hole to let light through the lens to hit the image capture device whether that be a digital sensor or film.  The larger the hole, the more light it lets through.  The more light it lets through, the shorter amount of time you need that light to hit the sensor before it is properly exposed resulting in a faster shutter speed.  Easy?  Sure.   A “fast” or large aperture is recognized by a lower number (ie: f/1.4, f/2, etc.) which is a larger “hole” to let light in through.  If you remember “f-stop” from high school photography class, you are more or less familiar.  A lens is normally designated by its maximum (largest) aperture.  As an example, the picture above was taken with a 20mm f/1.7 lens.  f/1.7 is the largest I am able to open the aperture up to on that lens.  I can always “stop down” the lens which means setting it to a smaller physical aperture.  The reason to set a smaller aperture on any given lens would be to gain depth of field (the area in focus), cut down the available light, or allow for a slower shutter speed.  To avoid too much confusion regarding f/stop or the aperture of a lens, the f-stop number is the focal length divided by the effective aperture diameter commonly shown in a ratio printed on the front of a lens 1:2.8, or 1:5.6, etc.  Basically, the smaller the number numerically, the larger the aperture.  If you have a zoom lens, there may be two f-stop numbers like f/3.5-5.6.  This means that the largest aperture on the wide end of your zoom lens is f/3.5 and when you zoom out to the longest focal length, the largest aperture available to you is f/5.6.  The other function of the aperture is its control over your depth of field, or area in focus.  The larger the aperture (the smaller the number ie: f/1.4, f/2, etc), the narrower or shallower your area in focus, the smaller the aperture setting (larger number ie: f/16, f/22, etc), the deeper your depth of field, or area in focus, is.

Aperture setting in full stops: f/1.4,  f/2,  f/2.8,  f/4,  f/5.6,  f/8,  f/11,  f/16, f/22, and then some lenses stop down, or open up even further.

#3 – Shutter Speed

The shutter speed is probably the easiest to explain as you are literally capturing a fraction of a second in most cases.  Generally speaking, if you want a crisp, sharp image you would shoot at a faster shutter speed effectively capturing a smaller fraction of a second and freezing even the quickest of movers.  The tricky part to a fast shutter speed is that you need enough light to properly expose the subject right?  This is where the exposure juggling dance starts to get fun.  Basically speaking a faster shutter speed is used to freeze action while a slower shutter speed will blur action.  A rule of thumb regarding shutter speed; 1 over the effective focal length for hand held shooting = sharp shots.  If you have a 60mm lens and are shooting on a full framed digital, or 35mm film camera, keep your shutter speed to at least 1/60 second.  If you are on a compact or cropped sensor digital camera, there is a multiplication factor to establish the “effective” focal length.  Your mileage may vary, also technique may not work depending on alcohol or caffeine intake.

Shutter speed settings in full stops: 1 second,  1/2 sec,  1/4,  1/8,  1/15,  1/30,  1/60,  1/125,  1/250,  1/500,  1/1000,  1/2000,  1/4000,  1/8000

Okay, now I have listed the three components in the Exposure Trifecta, and here is how they dance together.  Lets start by stopping.  The term “stop” is just a term for an incremental measure of exposure value and the term used in photography when referencing one of these three components (ISO, Aperture and Shutter Speed.)  It is no coincidence that the “stops” above are doubled with each adjustment as each stop effectively decreases (or increases depending on which way you’re going) the amount of light by half, (or double).  For instance f/2.8 allows twice as much light as f/4,  ISO 100 is half as sensitive to light as ISO 200, or 1/30 second will allow twice the light in as would 1/60 second.

Without a base to start from, we will utilize the “Sunny 16” rule, by where as a rule of thumb, you would gain proper exposure in full sun by estimating your shutter speed by matching your ISO while at f/16.  If shooting at ISO 100, set shutter speed to 1/100 (I know, it is not a “full” stop setting, but stick with me), ISO 200 then 1/200, etc.  For instance, if I were taking a picture of my dog at the park on a bright sunny day at noon, and my camera’s light meter didn’t work, I would start off by setting my exposure manually as follows:

ISO = 100

Aperture = f/16

Shutter speed = 1/100

This would probably get me very close to proper exposure.  But, what if my dog had just seen a squirrel and was running around like she was on fire?  1/100 of a second might not be a fast enough shutter speed to effectively freeze her in the picture.  Well, I would start by adjusting my Aperture, opening it up a few stops, lets say 3 for the sake of argument, so f/16 > f/11 > f/8 >f/5.6 (remember the smaller the number, the physically larger the aperture.)  So now I have opened up my aperture by 3 stops.  To achieve the same exposure, I would then increase my shutter speed by 3 stops, 1/100 > 1/200 > 1/400 > 1/800.  So, now I am able to freeze the crazy dog by shooting a shutter speed of 1/800 of a second while still maintaining proper exposure.  Now what happens when I get home and the baby is doing something cute, but the curtains are drawn and it is pretty dark in his room?  With my camera settings still at ISO 100, f/5.6 and 1/800 I take a picture and it comes out like I took a picture of a piece of coal at midnight, in Alaska in the winter.  We are now moving away from the Sunny 16 rule into the realm of dealing with whatever light we have available rule, so we’re flying by the seat of our pants now.  I need to open up my aperture to let more of the available light in, (and more than likely increase my ISO as well as slow down my shutter speed) so that the camera can see what I see.   So lets say that first I increase my ISO 3 stops from 100 > 200 > 400 > 800 and open up my aperture 3 stops as well from f/5.6 > f/4 > f/2.8 > f/2, to let more light in through the lens and create a higher sensitivity to that light by way of the ISO.  Now I can see how a shutter speed of 1/800 of a second looks and adjust to a slower shutter speed if the picture comes out dark, or faster if the picture comes out too bright.

Exercise Time!

Assuming you are working with a digital SLR camera, or a compact camera with a manual (M) setting, switch to that now.  Refer to your manual if you need a little guidance as to how to adjust your Aperture, Shutter speed and ISO settings. The beauty of digital (assuming we are all shooting digital) is that the feedback is instant, the learning curve quick and the wasted frames waste only the time it takes to delete them.  No chemicals, paper or ink needed to see if you messed up the exposure, so take a shot.  Pay attention to your light meter.  The light meter will be in the viewfinder or on the LCD screen that should show a meter with the digits -2..-1..0..+1..+2 as well as a marker hovering above or below it.  The marker is showing, based on your settings, how the picture is exposed.  Again, I will leave out metering settings and exposure compensation for the time being, but we will talk about that later (okay, it’s later).  For now, try to adjust your shutter speed and aperture so that the marker stops on the “0” which is stating that the camera has been satisfied that the light that is hitting the sensor is properly metering for 18%/middle gray (midtone), or an easier way to think of it would be that it is just right.    From here, you just play with settings until you get it to where you want it.  Move your mark to the right to brighten up the scene, or left to darken the exposure.  Once you have a properly exposed picture, try slowing the shutter speed by one stop and closing down the aperture 1 stop while keeping the ISO setting the same.  The picture should be exposed properly again, although by slowing the shutter speed down, it may have affected the sharpness depending on how slow a shutter speed you’ve adjusted to.

If you aren’t getting a fast enough shutter speed to freeze action while getting your exposure where you want it, open up your aperture more (down to smaller numbers).  If you’ve opened up your aperture as far as it will go, then increase your ISO setting until you get the exposure to where you want it.  Exposure is only a matter of stops, and you can usually get there in a variety of ways.  It depends on which of these three settings you want to manipulate for different effects which we will look at a little bit later…

Any questions, post them in the comments and I will be by sooner than later to help out.

Until then, enjoy and have fun.

For more reading try these posts:

Aperture!

Metering and Exposure Compensation, which, when, why?

Focal length, crop factor, field of view.

RAW vs. JPEG

Which lens for which situation?