Choosing a Lens
It is not as easy as it seems, choosing a lens for shooting pictures, that is. Most people, however, will pick a lens without thinking and seemingly capture great images at times. They are just plain lucky. You would think there is nothing to it, choosing the right lens that is. But there is a bit of science involved in it as well as some amount of visual aesthetics. But don’t get taken aback by reading this. It is not rocket science, and will come to you as second nature when you do it more often. The thing is all lenses are designed to take images pretty much the same way, but they have some inherent differences which allow you to control the angle of view, perspectives and visual attributes. Great photographers know this by heart, and of course because they shoot more often. They know which lens is capable of what. Beginners often pick a lens to shoot with without giving much thought to it, as a result never fully realizing what their gear can actually do for them. Hopefully, the following tips will help you to select the right lens for the situation.
Depth of Field
Depth of field is defined as the extent of an image that is acceptably sharp. Very simply, bigger the f-number (smaller aperture) that you use, more will be the depth of field in an image. On your lens you will have markings such as f/3.5, f/5.6, f/8, f11 and so on. If you don’t have those markings, don’t worry, you can simply switch your camera to aperture priority mode (that is Av on Canon and A on Nikon) and turn the command wheel to see the range of aperture values that your lens can stop down to. You will need to turn on the info display at the back of the camera prior to that.
All lenses can stop down to something like f/16 which should bring everything in front of the lens in focus, giving you a bigger depth of field. On the other hand, when you use a smaller f-number, such as f/4 or f/2.8 or even f/2, the depth of field becomes shallow. At something like f/1.2 the depth of field is very narrow indeed. Not all lenses can, however, give you the flexibility to use a really small f-number. Cheaper lenses such as the 18-55mm kit lens will only open up to f/3.5. A 50mm prime (fixed focal length) lens, on the other hand, can open up to f/1.8 or even f/1.4, giving you a really shallow depth of field. Additionally, cheaper lenses will suffer from what is known as lens diffraction, quicker than more expensive lenses. This causes the image quality to be softer when you stop it down to something like f/11 or beyond.
If you have a camera with a high resolution (larger megapixel) try not to use a cheap lens, especially when shooting landscape photos. This is because performance of cheaper lenses tend to get softer at something like f/8. Cameras with higher resolution accentuate that softness resulting in really soft images.
Angle of View
Angle of view, simply speaking is the extent of the scene that you can capture with a lens and camera combo. It depends on the focal length of the lens that you are using as well as the size of the sensor behind the lens. For a prime lens the angle of view is fixed as you cannot zoom in or out to capture a smaller or larger angle of view respectively. Plus, lenses with a shorter focal length will capture more of the scene than longer lenses, meaning angle of view is more on shorter lenses than on tele-lenses. This is the reason why landscape photographers will always use a wide angle lens to capture more of the dramatic scene in front of them. Smaller sensor powered cameras will capture only a fraction of the light that is coming through the barrel of a lens which gives you the same effect as if you the focal length is extended (mind you, actual focal length of the lens does not change, irrespective of whether you are using an APS-C or a full-frame camera). Let’s say you are using a full-frame Nikon camera (D600, D800 etc.) and you mount a 50mm f/1.4 prime lens on it. The angle of view on that camera will be 46 °. Now if you mount the same lens on an APS-C camera (D5100, D3200 etc.) the angle of view will be only 31’30 °.
Prime vs Zoom Lenses
Prime lenses have a fixed focal length. This means these lenses offer only a fixed angle of view. There are plusses and minuses on both sides, but the choice you end up with is entirely dependent on you. I personally believe that they each have a specific place in your kit bag and one just compliments the other and not merely compete with each other. You would need a zoom lens when shooting wildlife, landscapes or sports. A prime lens is just not versatile enough for such requirements. A prime lens, to be fair, is ideal when you are shooting inside the studio or when shooting still life. Prime lenses have less moving parts inside, something that makes it possible for manufacturers to concentrate on the optical quality of the lens. Zoom lenses, though are also great in quality, but because of the larger number of parts inside it, are heavier and more complicated to build. Pro photographers prefer these to zoom lenses because with these they have to spend less time adjusting focal length. Resultantly, they have more time to shoot images. Prime lenses are great for story-telling, because they tend to keep the same perspective and angle of view. The effect is never the same with zoom lenses. Popular use of prime lenses are in street photography and when shooting still life. A 50mm or even a 35mm prime lens is thus the perfect focal length for shooting street photography. Similarly, a 135mm or even a 200mm prime is perfect for shooting portraits.
Photography aspires to achieve the impossible, capture something that is three dimensional on a two dimensional plane. This creates a degree of perspective distortion that is difficult to counter for. Distortion is something that is inherent with photography. It denotes the distortion that happens when you represent a three dimensional subject on to a two dimensional plane. Let’s take an example. Let’s say your model is standing against a fence and there is a house at the backend. The fence will appear to be angled inwards towards the middle of the image, although in real life it is straight. The house will appear smaller than your subject. This happens because lenses create a sense of perspective depending on the focal length and also on the basis of how you use it. You can change the perspective by moving in or stepping back. With prime lenses photographers have no choice but to use this technique to be able to create compelling images. Please zooming in or out isn’t the same thing as changing perspective. You are merely changing the composition.