Week 2 – Introduction: Understanding exposure

It’s time to pick up our camera’s and start taking some pictures.  I will start with a discussion of the three basic components of exposure.  Exposure is the art of making sure the image we make in our photograph is the correct brightness to actually represent what we are photographing.  In fact we are able to make our photograph both brighter or darker than the actual image, and usually some parts of our image show up as brighter and others as darker.  This is an unfortunate characteristic of the sensors we use to take photographs.  For now, however, lets just take a look at the basic building blocks of our exposures: aperture (or f-stop), shutter speed, the ISO setting, and most importantly the amount of light available.  Though you can change all four of these factors, we will assume for the time being that we are working with natural light (not flash or strobes — we will get to these later), so we will focus on the first three, aperture, shutter speed and ISO.  This weeks assignment will actually focus on aperture but we will need to talk about all three so we have a basic picture of how they fit together.

The adjustment of these three factors adjusts the brightness of our image.  For a given amount of light in our environment there are combination’s of these factors that will work to make the exposure you want, and combinations that will not.  Given that you want a certain artistic outcome in your final image, if you choose any two of these, there will not be a choice in the third.  In fact, there are limits on all of them that may make the combination you want to use impossible.  You always have to balance these things together.  They each affect the amount brightness in your image in a different way. As well, each of them also have different secondary effects on our images.

1. Aperture or F-stop. The aperature is literally a tiny opening somewhere deep in your lenses that allows a certain amount of light to pass.  We can make this hole larger, or smaller in order to allow more or less light in for a given amount of time (shutter speed).  This hole is measured in a unit called the f-stop.  The larger the F-stop number the smaller the hole and the less light it will let in.  So an f-stop of 32 is actually smaller than an f-stop of 8.  The largest f-stop a lens has is often referred to as the speed of the lens.  A lens with a smaller f-stop number, a larger opening, is referred to as a faster lens — because it will allow us to use a faster shutter speed in a given lighting condition.  Aside from the amount of light that a given f-stop will allow onto our pictures, the aperture also affects the depth of field of our image.  Depth of field is how far into the foreground and background our photograph is in focus measured from the subject that is actually focused on. A smaller aperture will allow less light to expose our photograph but it will make more of our foreground and background in focus around our subject.  This may or may not be what we want.  If our background is distracting it may be better to use a larger aperture (smaller f-stop) to make sure it is not in focus.

2. Shutter speed.  This is how long we actually expose our image sensor to the light produced by the scene.  The basics are actually quite intuitive.  If you leave your shutter speed open longer more light will come in and your exposure will be brighter.  Keep in mind however, that if your subject moves during the exposure time it will cause the image to blur.  More importantly, if we move while the shutter is open our whole picture will blur.  A faster shutter speed will minimize this affect.  In general we want to use a shutter speed that is at least as fast as the focal length of our lens is long (don’t forget the crop factor of your camera).  So if your lens is a 200mm lens and you are using it on a 1.6x crop factor camera the actual focal length you have is 200*1.6=320mm so your slowest shutter speed you should try and handhold that lens at is 1/300th of a second.  If you want to use a slower shutter speed you will need to use a tri-pod or some sort of image stabilization system (available on lots of newer lenses)

3. ISO speed.  On a digital camera the ISO speed is how much amplification the camera applies to the exposure in the camera.  On a film camera it is how sensitive your film is to light.  A higher ISO setting is one in which your sensor or your film will make a properly exposed image for a lower amount of total light (ie shorter shutter speed, or larger f-stop, or smaller aperature).  Unfortunately, in both film and digital there is a negative impact to a higher ISO setting.  They are kind of the same thing (not really but similar).  A higher ISO film is grainier,  the “dots” that make up the image are larger, so there is lower resolution.  A higher ISO setting on a digital camera is “noisier”  there will be more individual pixels in the image which are over exposed or exposed in a weird color, in effect, there will be light colored specs in the darker portions of your image and your resolution is not as good.

So — how do the three of these things work together?  Lets simplify things a little.  You will usually want to use the lowest ISO setting you can which will allow you to set the other two where you would like.  When you are starting out, set your ISO as low as possible and check your exposure for the other two settings.  Can you get a fast enough shutter speed so that your image is sharp? Can you use the f-stop that puts everything you want in focus?  If not then you may have to increase your ISO — otherwise leave it where it is.  As for shutter speed and f-stop if one goes up the other will have to go down to maintain the same amount of exposure (brightness) in your picture.

Before we go any further you will want to ensure that you know how to adjust each of these settings on your camera. Grab your manual and look up a few things. What dials change f-stop, shutter speed, and ISO speed?  Do these dials change if you are in a different picture taking mode with your camera?  Tomorrow we will start our assignment by looking more precisely at the effect of aperture on our images — so make sure you understand how to put your camera in either aperture priority mode or manual mode, and how to read your in camera light meter to properly adjust for a correct exposure with different apertures (i.e. choose the correct corresponding shutter speed)

Until tomorrow — happy shooting

ART WOLFE-Digital Stock Photography-Nature and Wildlife Photography

Some incredible photographs, by one of the best check out this page — ART WOLFE-Digital Stock Photography-Nature and Wildlife Photography.

Welcome to our weekly photo assignment.

Welcome to our weekly photo assignment.  I am Jason, I have been an independant photographer for 15 years.  I have run the transition from full manual film camera, to my newest digital SLR system.  I am sure I will discuss camera equipment in the future as equipment always catches my interest, however, my primary goal with these posts is to move in a logical progression through the often complex world of digital photography.

Throughout these articles I will be completing the assignments myself, as well my partner who is relatively new to photography.  We will be posting some of our results and critiquing our photo’s as we go.  We would love it if you also posted some of your images for us to view as well, both the successes and the mistakes.  After all, we all make mistakes, and the most important thing we can do is learn from them.

I hope that we will provide you with some new and challenging assignments for you and your new digital slr camera.  We will be adding a new assignment on a weekly basis to help new and budding photographers develop and hone their camera skills.  We will also be discussing more details about the assignments throughout the week as we go.

Read on tomorrow for week one’s assignment.

 

Jason