On my last post I began to talk about what a camera is, and about how important it is to understand the basics of the camera, the light meter and exposure so that we do not become slave to automation. Now, I’d like to discuss three ways in which we can control exposure.  We can change the ISO setting, alter the shutter speed, or alter the aperture.  In today’s post, I’ll explain in more depth what these choices mean, starting off with what ISO accomplishes.

ISO stands for ‘International Organization for Standardization.’  Before digital sensors existed, a photographer’s photosensitive material was film, and some great photographers still use film today.  Film comes with an ISO rating that tells you how sensitive to light the film will be. The larger the ISO number, the more sensitive to light it is.  For example, a film with an ISO rating of 100 is a lot less sensitive to light than a film with a rating of 800.  For difficult light situations you use a film with a higher ISO rating.  When you are shooting on a sunny day, you usually want to choose a film with a lower ISO rating.

Film is a clear piece of flexible plastic coated with a thin layer of emulsion suspended in gelatin.  Film contains a chemical compound of light-sensitive material called silver halide that is covered with a protective layer to shield it against damage when handled.  It has an antihalation layer that helps give the image sharpness, too.  Color film has three additional layers of emulsion that are sensitive to blue, green and red light.

We are more fortunate today because digital cameras have digital sensors, and along with it, the ability to change ISO on each shot in order to adapt to different lighting realities.  Many cameras today have the capability of an ISO rating higher than 2400, which is quite an improvement over film.   Years ago, if you bought a role of film it had either 36 or 24 exposures.  You were committed to that ISO rating till you finished the entire roll of film.   Today we can change the ISO on each photo.  However, choosing a higher ISO rating in order to capture an image has its failings, too, especially when you get into the highest ISO ratings.   A high ISO gives a photograph what is called grain, or digital noise.   With film, this refers to the large clumps of developed metallic silver that occurs on the photographic image, which can lead to a less appealing image.  With digital images you experience a similar affect.  In general, it’s best to use the lowest ISO possible with your film or your digital sensor.  For more information on film speed please go to this link: http://wiki.answers.com/Q/What_does_ISO_stand_for_in_cameras.

In addition to ISO, the photographer can control his exposure with two other options; shutter speed and aperture.  Shutter speed is the mechanism by which a photographer can control the amount of time light falls on this photosensitive material.   Remember the light-filled box we talked about before?  The shutter sits right in front of the sensor, or the film.  To the left is a chart showing some basic shutter speeds available on most cameras.  The shutter will open for a set time once the photographer adjusts the shutter speed dial.  A photographer has choices that range from a shutter speed  of 1/2000th of a second to a shutter speed for a number of seconds.   Your shutter will have most likely have a B, which stands for bulb and allows you to keep the shutter open for as long as you depress the shutter button.  Below is a chart of possible shutter speeds on your camera.

Aperture is an opening on your lens created by a series of overlapping blades that allows light onto the photosensitive material.  Aperture is adjustable on most lenses.  You control aperture like you control shutter speed.  Each camera has a series of F-stops, which refers to the size of the lens aperture.  Lens aperture refers to the actual opening while F-stop refers to a measurement of that opening.  Your lens has a number of full F-stops usually starting somewhere near f/1.4 and ending at f/22.  It’s a bit counterintuitive because the smaller f-stop numbers let in more light than the larger f-stop numbers. Take a look at the image below if it’s confusing to you.

I’ll give you the science behind f-stops but you need not remember it.   You take the focal length of your lens and divide it with the diameter of the lens opening.  Therefore if you have a 50mm lens on your camera and your aperture opening is 25 mm, you have an f-stop of f/2.  If you have a diameter that measures 10 mm on the same lens, you have an f-stop of f/5. *

Here’s where it gets interesting.  Shutter speed and aperture work together to create a proper exposure.  If you move your f-stop up one stop from f/5.6 to f/8 you must stop down your shutter speed one stop to compensate.  For example if your light meter tells you that the proper exposure for your photograph at f/5.6 is 1/250th of a second, and you want to move your f-stop to f/8, then you must set your shutter speed to 1/125th of a second in order to double the amount of time light hits the sensor because you’ve decreased equally with a smaller f-stop opening.  Say you want to move your f-stop up three stops from f/5.6 to f/16.  If your shutter speed tells you a proper exposure at f/5.6 is 1/250thsecond, then you must place the shutter speed at 1/30th of a second, three stops down.

When using f-stop one encounters the issue of depth of field. Depth of field is the area of sharpness in a photograph both before and behind the focal point of your image.  For example, say you are taking a portrait and you focused on a person’s nose in your photograph.  There will be an area both in front and behind that focal plane that remains sharp. Have you ever seen a portrait where the nose and eyes were in focus but maybe the person’s ears weren’t?  That was done with a very shallow depth of field.  Have you seen a photograph where the mountains in the background were in sharp focus along with a flower in the foreground of the image?  That was done with a deep depth of field at f/22 or greater.   You control depth by with the choice of aperture, the distance you stand from the subject, and with the focal length of the lens you have chosen.  A picture taken with an large F-stop like f/2 will have a shallow depth of field while a photograph taken with a large f-stop like f/16 will have a deeper depth of field. We’ll talk more in detail about this in a later blog so don’t worry if it sounds a bit confusing.

It’s when the photographer begins to fully master aperture, shutter speed and ISO that he can start making interesting creative choices in his photography.  Bryan Peterson, the acclaimed photographer, points out in his excellent book,Understanding Exposure; that you have a total of six different choices when determining proper exposure.  All are correct exposures but only one exposure will be fulfill your creative intent.   A proper exposure of f/16 at an ISO of 100 with a shutter speed of 1/30th of a second is the same exposure as f/5.6 at an ISO of 100 with a shutter speed of 1/250th of a second.

Your head might be spinning a bit right now with all this information.  You might want to return your camera to the automatic setting and keep it there for good.  But don’t.   I’ll get more into how these three tools can be manipulated to make truly creative choices with your photography.   In the meantime, I highly recommend putting your camera settings on manual and experimenting with shutter speed and depth of field in a controlled environment. Maybe you can take an hour or two a week in your own home to experiment with the controls?  You can take images at different ISO settings to see how digital noise affects the image.  You can take some personal objects, set them up for an image, find the proper exposure and stop your camera down from f/16 to f/2 to see how depth of field works.  You can play with shutter speed too.  But beware,  a shutter speed lower than 1/30th of a second will give you camera blur if you aren’t using a tripod.  So use a tripod if you intend to go lower than that.  Also, I recommend you search the Internet  for the websites of photographers you admire, and study them to see how they use both f-stop and shutter speed to create their images.  Until then, I hope all this information helps the newcomer.  If you have questions or comments, feel free to email me.  I’ll try to answer them best I can.  In the meantime, happy experimenting.

When I was a child, my grandmother bought herself a fancy Polaroid.  It represented the latest in camera technology.  Not only was it fully automatic, it produced prints magically.  All you had to do was snap, shake, and wait.  Within minutes, your photograph would appear.  Despite, all this high-end automation, my grandmother had a tough time taking a good photograph.  Things were either overexposed or underexposed, or we had red-eye, or some heads were cropped out of the photograph.

Ansel Adams said of photography, “ If we fail to comprehend the medium, or relinquish our control to automation of one kind or another, we allow the system to dictate the results instead of controlling them to our own purposes.”  My grandmother was a classic example of what Ansel Adams was talking about.  She was slave to her camera’s automation.  Having no understanding of the basics of photography, her photographs oftentimes came out awful.  Many people come to me with questions about their cameras.    More often than not, they have invested a good sum of money on a fancy DSLR with lots of bells and whistles, and they are confused because they are having a hard time taking the photographs they want to take.  Usually, they place their camera on automatic mode.  They let the camera make all the decisions for them.   They cannot figure out why their photos did not come out they way they envisioned them.   I think putting your camera on automatic or program mode is like buying a Ferrari and setting it on cruise control moving along at only 45 miles per hour.  You get to your destination, but without utilizing all of your car’s potential.  You might as well have bought yourself a Toyota Celica because it will get you to your destination just as nicely and cost you a lot less.

That’s why I tell people who are thinking about investing money on an expensive camera to think about buying a point and shoot camera first, particularly if they have no interest in learning the basics of photography. There are many times when a point and shoot will do just fine.  I took a Canon PowerShot SD 6000 to Tanzania and I got a bunch of great, high-quality shots.  It is a wonderful camera and I still use it whenever I don’t care to lug my Nikon D300 with all its lenses around.

For those who have gone ahead and bought that expensive camera, and want to learn the basics, I dedicate these next blog entries to you.  You are that eager neophyte who wants to master your camera so that you can make better, more creative photographs.   So the first thing I’ll discuss about photography is exposure.   But in order to understand exposure better, it might help to talk about what a camera is exactly.

Think about your camera.  What is it and  how does it work?  Well, basically, your camera is a light proof box with a lens attached to it.  It allows light inside the box, which splashes onto some type of photosensitive material.  That photosensitive material used to be film.  Today it is most likely a digital sensor. How much light you let in, and for how much time you let that light into the box is how you control exposure.  If you have an SLR like my Nikon you view, focus, and compose the picture through a viewfinder which aligns with your lens.  Your camera contains a reflex mirror that sits right behind that lens.  Light reaches your eye through the viewfinder with the help of that mirror. It goes through a prism on the top of your camera, flipping the image right side up for you.  Behind the mirror you find the shutter, and behind that is where the light sensitive material sits.   Not only do you compose your photograph in the viewfinder, you  control exposure by reading the light meter located at the bottom of your viewfinder.  Your camera is most likely like mine, adhering to the 35mm format, which in the film days meant it created a negative measuring 36 x 24 mm. That makes it a 3:2 format.  This is far the most popular format for photography.

So what do we mean when we talk about a photograph’s exposure?  Exposure refers to the action of light falling on this photosensitive material in your camera.   If too much light hits it, the image is overexposed.  If too little light hits it, the image is underexposed.   When the proper amount of light reaches it, the image has a proper exposure.    You determine your exposure by pressing down on your shutter release button, which lights up the meter at the bottom of your viewfinder.  On my next blog post, I’ll talk about the three controls we have when determining proper exposure.