A few weeks ago, you purchased a digital single lens reflex (dSLR) camera for the first time. You were excited about all the pictures you were going to take – they were going to be way better than those pics you were taking with your cell phone.
Of course, there was a bit of a learning curve with all the buttons, settings, and adjustments, but after exercising your Google-fu and practicing a bit on your own, you learned quite a bit in a relatively short time and you are a bit proud of yourself. You aren’t a master photographer quite yet, but you have quickly learned that there is a relationship between a camera’s:
- focal length: the ‘35’ in a 35mm camera; the larger the number, the greater the zoom, and the greater the distance between the image sensor (‘film’) and the aperture
- aperture: a measure of how big the hole in the lens is, the hole allows light to pass into the camera. Measured in a fraction of the focal length (e.g. f/3.5), the larger the aperture number, the smaller the hole that the light passes through
- shutter speed: the amount of time the camera lens allows light to enter the camera, usually measured in fractions of a second
- ‘film speed’: perhaps you remember going to the store to pick up 200 ISO or 400 ISO film for everyday use, before the advent of digital photography…the larger the number, the more light sensitive the film (the values are standardized by the International Standards Organisation, thus ISO)
Fig 1. The cat in the foreground is overexposed.
You have been tinkering with the dSLR for a few weeks now, and you have a pretty good feel for things. You have come to realize that there is an ideal amount of light that needs to strike the image sensor (virtual ‘film’) to create a good picture. If too much light strikes the sensor, the picture will be over-exposed and will appear too bright (Fig 1). If too little light strikes the sensor, the picture will be under-exposed and will appear too dark (Fig 2). You now appreciate that the lighting in your environment dictates the ISO you choose (200-400 for daylight, 1000+ for low light conditions – but be careful, the more sensitive the ISO, the worse the noise). You realize that if your subject is moving, you need a faster shutter speed so that the picture isn’t blurred. You understand that a faster shutter results in less light hitting the sensor, so (in that instance) you would need to compensate by increasing the aperture size (ironically adjusting the value smaller, because it is the denominator of a fraction, whose value you wish to increase).
Fig 2. The building is underexposed.
Now imagine for a moment that you just purchased a new lens for your dSLR camera. The lens that you received with the camera (often referred to as your ‘kit lens’) quickly proved to be inadequate (you think) and you needed to upgrade so that you could take pictures with more flexibility than was afforded you by the simple 18-55mm f/3.5-5.6 lens you have been using. Some folks will go to a reasonably priced prime lens as their first lens purchase, but many (like yourself) decide to go with a bigger ‘zoom’, so they obtain what is termed a ‘telephoto lens’. In this instance, you have selected a lens that should work in most instances under typical lighting conditions: an 18-300mm f/3.5-5.6 lens.
If you are not a photographer, perhaps it would instead be easier (at this point) to imagine that you have just graduated from PT school and you realize all too quickly that – while you are now licensed to practice – your skills seem inadequate; you are not helping as many people as you may like, so you elect to go to a continuing education course. The course is designed to hone in on a certain aspect of your care and improve your expertise in that specific area. In doing so, you are improving your ability to ‘zoom in’ on a subject/patient. In other words, you have the basic know-how to operate the camera, but increasing from 55mm of available focal length to 300mm feels like completing the first 4 courses of a certification program – only (for $800 USD) the lens is considerably cheaper and is likely to bring you greater pleasure.
In many instances, though, while the telephoto lens helps you take pictures of things in the distance (i.e. birds or your kid playing a soccer game), you will quickly discover that the telephoto lens has limited utility. The farther you zoom in, the darker the picture becomes – the mechanics of the lens dictate that the aperture can move no larger than f/5.6. To compensate, you need to increase the ISO, which adds more noise to the picture. You could avoid adding noise by reducing your shutter speed, but now there is likely going to be increased motion blur in your picture. And then there is the issue with perspective…
What about perspective?
If you take a picture from the same angle each time, how can the perspective possibly change if it is taken with one focal length versus another?
Fig 3. Compressed Skyscrapers
Firstly, the picture taken with a telephoto lens will appear compressed or flattened. Look, for instance, at Figure 3, a photograph of skyscrapers which appear as though they have been built atop one another when photographed with a 300mm focal length. It is a neat effect in the photo, but the loss of depth is undeniable and often undesirable.
Secondly, the background of the subject photographed with a 300mm focal length from a distance is narrow; it is physically incapable of capturing the surrounding environment (see Fig 4).
Meanwhile, if you wish to photograph a subject in their environment, capturing context, you need to use a smaller focal length. You need to move closer to the subject, much closer. With a shorter focal length, the larger (f/3.5) aperture is now available so more light can come through the lens. With more light available, you can adjust down the ISO, reducing the noise in your picture as well. The closer you get to your subject (with your wide-angled, 18mm focal length), the brighter and clearer your picture can become and the greater your field of view.
Fig 4. The photo on the left is taken with a telephoto lens from a greater distance, the photo on the right was taken with a wide angle lens from close up
Of course, then you realize that your kit lens could shoot at 18mm too. Sure, every once in awhile, you may find a use for the 200mm or 300mm focal lengths, but (for the most part) you could have saved $800 and mastered the kit lens, instead. There are occasions when the extra focal length may be helpful, but you will not rely on it every day.
. . . .
In a competitive marketplace where every continuing education purveyor is trying to get you to buy their special telephoto lens – each with its own special features – consider honing your skills with the kit lens first and foremost. The small focal length on the kit lens is what encourages you to stand closer to your patient and develop a relationship. Moving closer to your patient helps clarify the picture you are trying to capture; it reduces the noise. The different/closer perspective affords you the opportunity to see more variables that surround, stress, and influence a patient embodied in their unique environment with its particular circumstances.
Fig 5. A telephoto view of the patient
The telephoto lens encourages you to zoom in on one area, only to zoom out and back in on another. The telephoto lens directs us to look at the parts, in isolation. It is the telephoto lens that separates the biological from the psychological from the sociological. The telephoto lens has fractured and fragmented our patients. The world is filled with clinicians with 300mm lenses – far fewer have mastered 18mm.
My only question: can you be a wide-angle PT?
Fig 6. A wide-angle view of the patient