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Focal length is the distance from the center of the lens to the image sensor (focal plane), and each lens has a different focal length. Focal length is important because it determines the range of a scene you can capture (angle of view). As shown in the following photographs, the shorter the focal length is, the wider range you can capture, while the longer the focal length is, the larger distant objects appear.

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Let's check the focal length of your lens. The range of the focal length available with the lens is printed on the lens. For example, focal lengths from 55 mm to 200 mm are available with the SAL55200-2 in the picture below. Also, on the mount side of the lens barrel (near the camera body), you can see the mark for the focal length currently set. In the picture below, the current focal length is 55 mm.

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Conclusions: Nearly half of the hospitalised patients were prescribed antibiotics and antibiotic associated DRPs occurred frequently. The drug risk ratio for the different antibiotic groups varied with a factor of six from the lowest to the highest. A high drug risk ratio would alert of antibiotics which require heightened awareness when going to be used in clinical practice.

This photograph was shot with a fixed focal length lens. By setting the aperture to a small f-number, the background is defocused to a large degree. Macro lenses, which allow you to take close-ups by getting closer to a subject, are also fixed focal length lenses. Although many recent zoom lenses have a macro feature with a fairly short focusing distance, their performance cannot match that of a dedicated macro lens.

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On the other hand, if you use a fixed focal length lens, which does not have a zoom feature, you have to move in order to affect the composition. However, fixed focal length lenses are usually faster and have a wider aperture. They offer advantages in expression involving defocused backgrounds and the ability to use high shutter speeds in low-light situations, reducing image blur. In addition, they have superior rendering performance, so you enjoy excellent image quality that cannot be delivered by a zoom lens.

Generally, lenses with a focal length of around 35 mm are called normal lenses, because they have an angle of view close to the human visual field. Lenses with a focal length shorter than this are called wide-angle lenses, and those with a longer focal length are called telephoto lenses. However, there are no strict standards for these terms. Use different lenses according to the subjects or images you want to shoot.

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Lenses are divided into two types: zoom lenses, which have a variable focal length, and fixed focal length lenses, which have a fixed focal length. Some zoom lenses are versatile enough to range from wide angle to telephoto by themselves. In addition to being useful for everyday shooting, these lenses are especially convenient for travel when you want to carry as little baggage as possible.

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In this picture, 55-200 on the left side is the range of the focal lengths available with the lens. The white line on the right side indicates the focal length currently set.

This photograph captured the details of a sunflower with a macro lens. With a macro lens, you can get this much closer to your subject.

Results: Out of the 668 patients included, 283 patients (42%) used antibiotics (AB users). AB users were older (76.2 vs. 73.9), used more drugs on admission (5.1 vs. 4.4) and had more DRPs (3.0 vs. 2.2) than non-users. The DRP categories no further need for drug, non-optimal drug and non-optimal dose were most frequently observed. The drug risk ratio, calculated for 12 antibiotic groups, was highest for aminoglycosides (0.77), beta-lactamase-resistant penicillins (0.56), macrolides (0.54) and quinolones (0.48) and lowest for first- and third-generation cephalosporins, 0.17 and 0.13, respectively.

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Methods: Patients from internal medicine departments in four Norwegian hospitals were prospectively included in 2002. Demographics, drugs used, medical history, laboratory data and clinical/pharmacological risk factors were recorded. DRPs were identified by clinical pharmacists and assessed in multidisciplinary hospital teams. A new term, the drug risk ratio, was established and defined as the number of times the antibiotic was associated with DRPs in relation to the number of times it was used.

Purpose: To investigate the use of antibiotics in hospitals, to explore drug-related problems (DRPs) linked to antibiotics and to introduce a novel way of expressing the risks accompanying use of various antibiotics.