While most lessons/tutorials on learning photography start with an understanding of exposure, my personal experience says that you start with trying to get stable, blur free images first. This goes hand-in-hand with the study of exposure and makes it simpler and faster to grasp in practical terms. As a bonus, the images start becoming better from day one rather than later.
Do take the time to look at the links here referring to articles on Wikipedia for more technically correct details as I will be mostly skipping details in the initial articles here. There is no need to understand all the math and details, but, a read through on Wiki would be quite helpful.
Before we can get to the basic practice of getting sharp, blur free images, it would help if we can understand the meaning of some of the very basic terms used in photography as related to a DSLR. Most of the current P&S cameras will also have these semi-automatic modes and some of this discussion is also applicable to them.
Firstly, photography is all about light, light and light. Light is what is captured by the sensor in a camera and translated to the images we see. Without proper lighting, the photos would either be noisy (grainy) or blurred. All cameras have a built-in light meter which detects the light in the scene you are trying to capture and sets other parameters automatically when it is in fully automatic mode.
So, what are these “other” parameters that the camera sets automatically? Turns out that the camera will set the shutter speed, aperture and ISO to achieve what it thinks is a correct “exposure” of the given scene. So, how is the “exposure” determined and what is it?
Research on the subject says that most of the “scenes” that we look around at are around the 18% grey mark. The light meter in the camera looks at the scene and sets parameters that would yield close to a 18% grey image for the scene. This is a very top-level, simplistic view of a complicated process in practice. We will go into more details later. For now, just keep in mind, if you photograph a white wall or object, the resulting image from the camera would be grey and not white. The opposite is also true. If you take a shot of a black wall or object, the image will be on the grey side and not quite black.
The “correct” exposure, in simple terms, is an image that comes out around 18% grey. In practice, this might vary between cameras, but, the principle remains the same. Most newer cameras have “scene” modes which “compensate” for the black and white exposure issues. Using the correct “scene” mode, tells the camera what you want to capture in the shot.
The other common issue is “focus“. When you point the camera at some “scene”, the camera has no clues on what you want to focus on or how to really expose the current scene as you see it. While we can set the “scene” mode to tell the camera the kind of scene we want, we also have to help the camera in focussing at the correct location. Most cameras assume whatever is in the centre of the frame should be the area of focus. This may or may not be valid in all cases. Consider a typical example of trying to photograph a bird on a tree. The camera, by default, will focus on all the branches and leaves in front of the bird rather than the bird itself. This is just one of the reasons why almost all cameras have some flexibility in setting the focus point where you want it.
Bear in mind that the camera is a generally clueless device and has to be helped along to perform a better job. The more help you can provide, the better the results. The final stage would be where you tell the camera what you want, exactly, and not just help the camera to make a better decision.
Let us begin by helping the camera to do a better job. In order to achieve this, we need to understand a bit more about how the camera works and the related terminology. Although I have already provided the Wiki links for these terms earlier, we will look at the same very briefly here as well.
This is the amount of time the camera opens the curtains that cover the image sensor to expose an image. Generally measured in seconds and most commonly used speeds are in fractions of a second. As a general rule, using a shutter speed lower than the focal length of your lens can result in a blurry image due to camera shake. Although most lens vendors offer some kind of stabilisation technology which alleviates this shake to some extent, you will have to experiment and see what shutter speed works best for your setup and gear. There is a detail of the sensor size, called the crop factor, which affects this and we will look at it later.
There are a couple of points to keep in mind here…The subject can also move causing a blurry image. Traditionally, a shutter speed of 1/125 is considered safe for human subjects. Pets, children and wildlife need a much higher shutter speed to freeze them. If we consider a flying bird, one would start at around 1/1000 of a second, increasing the speed as needed. Most entry level DSLRs have a shutter speed range from 30 seconds to 1/4000 of a second. If you use a flash/speedlite, the fastest shutter speed will be limited to around 1/200 of a second for most entry level DSLRs.
This is the size of the opening in the lens. The wider the opening, the more light that is let onto the sensor. Wider opening allows for better low light photography. Under the same lighting conditions, a wider opening will allow more light to get to the sensor with higher shutter speeds than would be possible with a smaller aperture. This is measured in f-number which is just the ratio of the focal length to the diameter of the opening in the lens. Since this is a ratio/fraction, the numbers used can be confusing initially. A smaller f-number means a wider aperture and vice-versa. For instance, f/1.8 (f1.8) is a wider opening compared to f/4 (or f4). Lens that have a wider opening of f2.8 or lower are also called “fast” lens.
This is actually the amplification used by the image sensor to lighten up an image. A far simpler way to understand it would be to think of this as the sensitivity of the image sensor in the camera. A higher number makes it more sensitive to light and allows shots to be taken in low light conditions. Generally, you would want to use the lowest possible number available on your camera to avoid any noise/grain on your photos. Making the sensor more sensitive to light also introduces noise in the image. Most modern cameras are fairly good at handling higher ISO numbers and you should experiment and see what range of ISO works best for your camera and lens with acceptable noise levels.
These are the 3 parameters that determine the overall “exposure value” of an image for any camera. This is often referred to as the “exposure triangle“. A change in any of these parameters will have an effect on the others.
Focus on the Subject
All DSLRs offer some variations of focussing modes. Most cameras have multiple focus points and allow you to select the kind of focussing and/or a specific focus point. Personally, I use the single, centre, focus point almost all the time. The only exceptions where I switch the mode to multiple points or tracking modes is for objects in motion. Even for slow-moving objects, like eagles floating around the sky, I remain with the single point focus. This ensures that I always have my subject in sharp focus. Most cameras use different techniques to focus when using the viewfinder and the LCD screen. There might be scenarios where one works better than the other. Prefer using the viewfinder as it will generally be far more accurate and will not drain the battery.
There are generally 4 creative modes on all DSLRs and most P&S cameras. These are usually referred to as the PASM modes. Why are they called creative modes? Simple, these modes allow you to control the camera parameters to get the effect and impact you want in an image and not what the camera “decides” is best.
In the P or Program mode, you set the ISO and the camera does the rest. In the A or Av mode, you set the ISO and aperture and the camera deals with the other parameters. Similarly in the S or Tv mode, you set the ISO and the shutter speed and the camera takes care of the rest. The last, or M, is what we are aiming to get to and achieve full control of ISO, shutter speed and aperture.
All of these modes allow shooting in RAW format. This is a very important factor to consider when using a DSLR. Most DSLRs will not allow RAW format saving for images shot in any automatic/scene mode.
We will be using only these creative modes and not any automatic ones. Which mode we select would depend on a variety of typical scenarios which we will get into later. For now, consider utilising the Program mode as a fully automatic mode that does not pop up the flash automatically and requires you to set the ISO as desired.
All DSLRs offer different ways to figure out the available light and set exposure parameters based on the same. This process is called metering. Once you start experimenting with the different metering modes, you will be in a position to figure out which one works best for your particular scenarios. In general, the automatic, evaluative metering will work fine most of the time to start with.
This was pointed out briefly in the introduction with a link to Wikipedia. All DSLRs have an exposure compensation setting. We will get more into this later. For now, for bright objects (white) you would dial in a positive compensation and for dark objects (black) you would dial in a negative compensation. Basically, what this does is to tell the camera to move up or down from its computed 18% grey. This way, a white wall will come out as white and not grey and the same applies to a black wall coming out black.
Now that we have covered some of the basics, let us start with getting to know our own cameras better. This will help before moving onto the next article(s) since I will try not to repeat the link references and points we have previously discussed.
As an exercise, before the next article, read your camera manual. If you have already done so, read it again and some of the material might make more sense. Ideally, carry the camera manual with you till you have used most, if not all, the camera features and are comfortable with all the buttons and settings on your camera.
To make sure you are familiar with your camera modes and functions, take the same shot in all different modes and examine the EXIF information from the fully automatic modes to figure out what the camera sets the exposure parameters to for your given scene/automatic mode. The EXIF information is a standard part of the image file regardless of which format you use to save the image in, raw or jpg. Ideally, to begin with, use the save as raw+jpg for this experiment and compare both images and try to figure out the differences.