So I bought a digital SLR. What now?

Perhaps you decided to upgrade your camera by going from a point and shoot model to a full-fledged digital single lense reflex camera.  Most of the time there is the expectation that a better camera will result in better pictures. But the results don’t seem to be a whole heck of a lot better than you had with your point and shoot. You are probably taking pictures with your camera set of P mode.

Digital SLRs, like films SLRs before them have a lot of settings that can be complicated and confusing. What I am going to try to do here is explain some of the common things that make up your digital SLRs and how manipulating your settings can take your images from good to WOW!!! I’m going to try to do it in plain ordinary English too. Most books you can get or camera manuals especially don’t do this.

Now there are three things which determine how your picture is taken (or exposed). There is film speed (or ISO), shutter speed, and f stop. Having a working understanding of the three things work together is pretty much paramount if you want to take great images and not just pedestrian snapshots.

Now before I get into that I want to talk about something called exposure value. It is simply a measure of how bright a scene is (or how bright the light is that is falling on the part of the scene that is most important to you and your image.) For the most part your exposure value is not something you can change. For instance if you are outside in open light, unless you are using some sort of artificial modifiers, you cannot change what your exposure value is. Think of it as a constant. Regardless of how you change ISO, shutter speed, and f stop, exposure value does not change. Indeed it is the basis of how your setting work together. I’ll come back to this after I explain what the three variables are and how they work.

Let’s start with ISO (or film speed). In the old days, before the advent of digital, your film speed was determined by what sort of film you were using. The lower number the film, such as 100 meant that it was less sensitive to light than 400 speed film. This was because the silver halide particles on lower number (or slower film) were smaller and resulted in a finer grain image. The higher number (or faster film) had larger silver halide particles and yielded a grainier image than the slower films.

Digital works roughly the same way. You will have a better quality image with a lower ISO number and a noisier image with a higher ISO number. Setting your ISO is usually the first thing you are going to do on your digital camera. I’ve found that in everyday lighting situations ISO 200 to 400 works well. If you are in a low light situation, then you probably want to go with a higher ISO like 1600. Remember your sensor (think of it as film) is more sensitive to light at higher ISO numbers.

Shutter speed is the amount of time your camera’s shutter is open and allowing light to create an exposure.  Some common shutter speeds that you are likely to see are:

• 1 second
• 1/2 second
• 1/4 second
• 1/8 second
• 1/16 second
• 1/30 second
• 1/60 second
• 1/125 second
• 1/250 second
• 1/500 second
• 1/1000 second

Notice that as you get faster from 1 second that at each interval the amount of time is halved. For instance 1/16 second is half the amount of time as 1/8. These intervals are commonly known as “stops.” For each full stop change in shutter speed as shutter speed gets faster, the exposure time is halved from the previous stop. Conversely as the shutter speed gets slower, then each stop results in a doubling of exposure time.

You should try to avoid really slow shutter speeds. I’d advise having shutter speeds no slower than about 1/60 of a second, the reason being that when your exposure times are long it is difficult to impossible to hold your camera steady for that length of time. In photographic terms 1 second is practically an eternity. You will get blurred images. Not good.

If you are taking a picture of a rapidly moving object you will need a faster shutter speed around 1/250 second or even faster if there is enough light. You want to freeze the motion. Using a slow shutter speed will not get the job done.

Now let’s talk about f stop. Essentially f stop is a mathematical ratio which is the focal length of the lens divided by the aperture (opening diameter) of the lens. Don’t bother to memorize that. It is not all that practically important.

Camera lenses have a set of blades inside of them which can open up or shut down in fixed increments. The amount of the lens opening diameter is called the aperture.

Now recall that when we talked about shutter speed we noted that each full “stop” is either a doubling or a halving depending on if you increase or decrease your shutter speed.  F stop works the same way. Each full f stop lets in twice as much or half as much light. The f stop names that you will commonly see are:

• f/2.8
• f/4.0
• f/5.6
• f/8
• f/11
• f/16
• f/22 

The lower number stops are larger apertures. The higher numbers, of course, are  smaller apertures.

Using a smaller aperture lets in less light so that will automatically force you to use a slower shutter speed to get a proper exposure. Conversely using a larger aperture lets in more light so the correct shutter speed will be faster.

What affects one affects the other. They are intertwined with one another in an unbreakable exposure partnership.

Why would you choose one f stop over another? That is because of something called depth of field. We’ve all seen those awesome images where a subject is in tack sharp focus, but the background is completely blurred. That is because the photographer choose a large aperture. The rule that is important to remember is that you have a shallow depth of field with large diameter apertures and deep depth of field with small diameter apertures.

Let’s return to exposure value. Remember that we said exposure value can more or less be considered a constant. Recall we said that setting your ISO is usually the first thing you will do. That leaves us with shutter speed and f stop. Also recall that when you change shutter speed and f stop by one full  “stop” you are either doubling or halving the increment.

Logically it follows to ask: what do I do next? Analyze the scene you are about to capture and ask yourself. Do I have motion that needs to be frozen? Do I want a shallow depth of field? If you want a fast shutter speed, then you will set you camera for a particular shutter speed using a mode on your camera called shutter or “S” priority. Set your shutter speed and then the correct f stop will be set by the camera to give you the proper exposure value.

If depth of field is your main concern then you want to set your camera on aperture or “A” priority mode. Your camera will pick the proper shutter speed for the exposure value that you are confronting.

Understanding this let me put forward another rule: If you change one thing, the other thing must also change by a corresponding amount. If you double your shutter speed by one stop, you must half your aperture size.

Let’s look at it like this. If your correct exposure looks something like 1/250 second at f/8 and you change your shutter speed to 1/500 of a second you have halved your shutter speed. You must double your aperture. Your correct exposure combination then becomes, 1/500 second at f/5.6. It is still a correct exposure for your exposure value, but the combination of shutter speed and f stop is different. Or if you change your shutter speed to 1/1000 second your aperture will become f/4. See how that works together?

This is only a skimming of the subject, but it should be enough to get you on your way. In the way of review let’s go through the steps.

• Choose an ISO based on the light level of your subject.]
• Decide whether a shutter speed or an aperture is more important to you.
• Setting one, the camera will select the correct value for the other.

I hope this post has been helpful. Digital SLRs can be a daunting challenge to understand, but grasping the simple principles I have described will get you moving in the right direction. Before long the rules of exposure will become second nature to you.

Happy shooting!!