A lot of people ask a question how to make a photograph catching the attention of others. One of the most powerful photographic techniques is to manipulate depth of field. It is also defined as range of focus. Depth of field is the most important photographer's trick. It is described as the distance on the photograph between the nearest and the farthest point on the scene which seems to be acceptably sharp. In other words the greater the depth of field the more details on the photograph appears to be sharp. Depending on the results which the photographer would like to achieve, he will take a shot with wide or narrow range of focus. Wide range of focus makes you feel that everything on the photo is important. And contrary, narrow depth of field makes you focus on the sharp area and everything else seems to be less important. Manipulating this control gives a photographer a lot of possibilities. In case of a landscape images should make better impression when every detail appears to be sharp from the foreground to the background. While for portraits, and many other subjects, the image would get more attractive if there is just the object to focus on and the rest fades gently into background. Some portraits get really interesting if only a small part of it is sharp, eg portrait made from the top with the strong focus on eyes of the model.
Now let's try to focus on the controls allowing us to achieve desired effects. First and the most important control affecting depth of field is relative aperture determined by F-number. Aperture is defined as the ratio of the focal length ofm the lens to the diameter of the entrance pupil, which is the opening the light travels through. The larger the F-number the smaller the opening and relatively the longer exposure time allowed which results in larger range of focus. From the other hand the high F value stands behind big entrance pupil and requires smaller exposure time resulting in small focus range. This is why lenses with small F number are also called bright lenses. Even though there are bad light condition, the photographer still can take a sharp photo using short shutter speed. If we talk about landscapes and we want to keep the high range of detail, the larger aperture the better, but you need to remember that if lighting conditions are not the best, longer exposure time is required. So if you plan to take a shot of a nice landscape do not forget to take a good quality tripod, particularly if you plan to stay longer and you might fancy to take some nice night photographs.
The second aspect influencing the depth of field is related to the lens focal length. There is a huge range of lenses available on the market starting from the Fish Eye lenses, through wide-angle lenses, medium telephoto lenses to long telephoto lenses. The first type covers 180- degree perspective and with this lense it is quite hard to achieve the narrow range of focus. Wide angle lenses are good to build depth depth of field and are the best lenses to take shots of landscapes. Surely all the rules are meant to be broken so if you have the idea how to use the other kind of lense to achieve something special do not hesitate to try it. With the wide-angle lens it is quite hard though to get soft, blurred background. The medium and long telephoto lenses would serve much better that purpose. With these lenses you are able to achieve only details sharp surrounded by the beautiful bouquet dependent of the quality and type of lense. Telephoto lens is perfect for capturing the animals and other nature objects from a far distance, the subject seems to be cut from the background. Lens is also suitable for sport photography. Medium telephoto lenses are usually used for making portraits.
The third point I would like to discuss is the distance between the focus point and the camera and between background and the focus point. To get the sharp object cut of the blurred background use telephoto lens and make sure the object is far from both camera and the background. If you use the wide-angle lense the object must be close to camera and far from background. If you wish to have both object and background sharp use again wide-angle lens and locate your object reliably far from camera (remember about the right F setting). The last combination will help creating nice and sharp family portraits quite often used for wedding photography to make sure every member of the family stays in range of focus.
The right combination of these three elements will help you to achieve effects you are looking for. The most important though is to be aware of it and use it in the appropriate way to avoid any surprise.