A lens lesson
Find out about the different kinds of lenses used in a camera so that you can create your own masterpieces someday.
You have read about lenses in your school curriculum. These are optical elements which can transmit and refract light, either causing the light beams to converge to a point or diverge. Here, we are primarily talking about the former one, which converges light rays to a point. They are also called convex lenses. But the lens of a camera (photographic lens) is not a single piece of glass as you might wonder. A regular photographic lens is a compound lens made up of a number of lens elements, which work together to converge the incident light rays to the photographic sensor. It’s important to keep in mind that every lens comes with some kind of optical flaw – some lenses distort the images, some fail to converge all the colours of the spectrum to a common point and so on. They are all called optical aberrations. Multiple lens systems are therefore required to counteract and correct (as much as possible) the many optical aberrations that arise. The lens designer balances these effects out and prepares a final design that is suitable for photographic use and bulk manufacture. Have a look at the lens, if you have the camera handy with you. You will observe a violet or greenish surface of the lens.
It’s not the colour of the glass. The lens surface is coated with some chemical to protect the material from damage due to reactions induced by contact with air, to prevent reflections, and to meet requirements for colour balance and rendition. Several layers of coating may be applied for the best colour and light transmission, but excessive coating can reduce the light that passes through the lens and limit its usefulness.
To understand different lenses that are used in wildlife photography, we must understand the concept of focal length. The camera lens projects part of the scene onto the sensor. The longer this distance, the bigger is the size of the image that is formed and this is the concept based on which the zoom/ telephoto lenses work. This distance is nothing but the focal length. So longer the focal length, more magnified is the image.
You will also come across two terms frequently: Prime and Zoom. A prime lens is a lens that has a fixed focal length. They range from wide angle ones to the longer telephoto ones. A zoom lens is a lens that offers a range of focal lengths to the photographer in a single lens. Simply put, you can manually move the barrel of the lens (and in turn the position of the optical elements inside) back and forth to achieve different focal lengths. The widest aperture of a zoom lens may change when you are changing the focal length but some of the lenses have a constant aperture value throughout.
These have become increasingly popular, as they give you the flexibility to shoot at both wide and longer focal lengths without having to switch lenses. A prime lens has high-quality optical elements. They also have lesser optical elements and hence have an excellent picture quality, are sharper, have fixed focal length and are quite costly. Zoom lens has more optical elements, have more flexibility with various focal lengths and are more affordable than prime lenses.
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