Depth Of Field
Depth of field is the area that is in focus (sharp) in front of and behind your focal point. In a photo with shallow depth of field less will be in focus. And if the photo has a wide depth of field more will be in focus.
The way to control depth of field is through your choice of aperture, focal point, the lens focal length and how far you are from the subject you are focusing on. The size of the sensor or film format that you use, will also affect your depth of field. Digital cameras with large sensors are very popular because they allow you to produce a shallower depth of field. The Canon EOS 5D Mark III is the camera of choice for many because it allows those interested in film to take advantage of this shallow depth of field and produce a cinematic feel for a fraction of the cost.
To keep it simple, I will talk about the aperture’s role in creating pleasing depth of field.
A small aperture (e.g. f/22) will produce a wide depth of field and a large aperture (e.g. f/2.8) will produce a shallow depth of field. It is often confusing to people that a small F-stop number represents a large aperture and a large number a small aperture.
An aperture F-stop number is the fraction of the lenses’ diaphragm (the hole through which light passes to expose the shot) that is open and that is why a large aperture of for example F2, is larger than F22.
So what do you do when you want to blur out the background in a portrait shot because you cannot find a simple, clutter free background? Stand your subject as far from the background as you can and choose a large aperture (small number). If you have a telephoto lens, choose this over a wider lens, as a wider lens will give you a wider depth of field.
This is a great technique unless you have a lot of light in the scene (i.e. a bright sunny day). When it is really bright outside, the correct exposure for the shot will call for a smaller aperture as there is already plenty of light and so you need to let less light into the camera, during the duration of the shot (via a smaller aperture). There are a few things that you can do here. If possible shoot on overcast days, as bright sunlight is not great for portrait shots or for choosing a large aperture. Another option is to dial the ISO down to 100 and then if there is still too much light for the shot, up the shutter speed to a higher number. If you are still struggling with too much light, you could change to a more shaded area or use a diffuser or scrim to take the light down further.
For a wide depth of field you have to think differently. Landscape photographers choose smaller apertures to get a lot of detail in the shot. They generally shoot with their cameras on a tripod, as they will often use longer shutter speeds to make up for the smaller F-stop. Whatever type of photography you are into, you must bear in mind the speed of the shutter when you choose a small aperture for a wide depth of field.
Moving objects will blur with longer shutter speeds, so you will have to assess the scene and make some creative choices. If there is an abundance of light, then you can choose a fast shutter speed and that may solve your problem. On the other hand, if there is not as much light and there are some elements in your shot that are moving, you will have to decide if you can live with the blur of the moving objects, or if you need everything sharp and in focus. It is also an option to change the ISO to a higher ISO, which will allow the camera to record more light. This will allow you to set a faster shutter speed, but this may come at a price as the higher the ISO, the more digital noise you will have in your shot.
As you can see choosing an aperture is not always as easy as it looks, as there are other considerations to think of. This is where planning comes into play! When choosing the time of day and the location think about the end result you want to achieve.
When you know what aperture you want to shoot at, you can plan in advance and take into account the amount of light you will need on location and consider supplementing that light with strobes if necessary, to get the shot.
Shooting in a studio with flash lighting is much easier, as you rather than Mother Nature, decides on the amount of light that is available.
Most professional shots are planned out in advance to take into account the look that the photographer is going for, so grab yourself some paper and a pen and start crafting the plan for your next work of art!
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