Cicero said, ‘Ut imago est animi voltus sic indices oculi’, which translated means, ‘the face is a picture of the mind, as the eyes are its interpreter’. Boil this down to its essence and you get, ‘the eyes are the windows of the soul’.
Philosophical or physical, looking in or peering out, it’s all relative.
The three key elements are eyes, window and soul. In its best sense, the photographer provides the soul, the camera its eye and the lens its window. Your eye may function perfectly, but if the window it’s looking through is dirty or distorted you’re view is going to be adversely effected and your soul is going to be inaccurately rendered.
So this article addresses those windows, which more likely, are known as lenses.
Generally speaking, there are three types of camera lenses. The wide angle, the standard and the telephoto. Each have a special purpose. The wide angle lens is useful when you are in a small room or if you want to be up close and personal with your subject. The standard lens is more less an all purpose lens and the telephoto is useful when you have more distance between you and your subject.
This is not to say each of the lenses can’t be useful in other situations. An example of this would be with the telephoto lens. A telephoto lens is often useful for portraits, because of its ability to blur the background. But in the interest of keeping this simple, we’ll leave those details for further exploration later.
Your question now may be, ‘How do I distinguish a wide angle lens from a standard or a telephoto lens?” As far as physical properties go, usually a wide angle lens will be shorter and stubbier, whereas a telephoto will likely be much long and the standard will fall somewhere between the two.
A much easier way to learn to understand focal lengths. The focal length is the distance between the optical center of the lens and the surface of the film or, in the case of a digital camera, its sensor. A wide angle lens will have a smaller number, usually 35mm or less. A standard lens is somewhere around 50mm and a telephoto 85mm or above.
You may ask, “What about my lens, it’s 28—135mm?” A lens with multiple focal lengths is referred to as a zoom. As you zoom in or out the focal length changes by moving the optical center of the lens closer or farther from the film or sensor.
A lens with a fixed focal length is called a Prime Lens. Many purest photographers insist that Prime Lenses are better and I would agree. The argument is that the lens was manufactured to do one thing best and this is usually the case. A zoom lens (especially an inexpensive model) will usually have a sweet spot either at its shortest or longest focal length.
There are sometime distortions or aberrations found at different focal lengths in inexpensive zoom lenses and this is why the purest will use prime lenses when available. As an example, I use a 17-40mm f/4 lens and the lens is clearly sharper at 17mm than at any other focal length. Is this a reason to use only Prime Lenses? No. There are many instances where using a Zoom Lens is essential.
I have been asked numerous times what Sharper means, in photographic terms. Two terms used in describing a lens are sharpness and softness. When a lens is extra clear when focused it is referred to as sharp. To be tack sharp is to be perfectly focused. On the other hand a lens called soft usually is not perfectly clear when focused—this is not to say it is out of focus. Often times certain situations will call for soft lens, such as in weddings or other portraits where a dreamy effect is desired.
Soft can also be a polite, yet derogatory term for a picture that is out of focus. And speaking of Out of Focus, OOF is an acronym you may come across that means exactly that.
The next term we need to address is f/stop. There are many debates as to what the f in f/stop means. Some suggest it is an abbreviation for fenestra, which means opening in Latin. Others for something as simple as fraction. Maybe it’s even easier to think of as Focal Length.
The reason I say this is that the Focal Length divided by the number that follows f/ is how wide in diameter the Aperture is going to be. In case you don’t know what an Aperture is it is the opening in the lens that the camera sees through. For example a 50mm f/2 lens when Wide Open will have an Aperture 25 millimeters in diameter.
Now you may be wondering what Wide Open means. Wide Open is when the Aperture is as open as it will get for the particular lens. The opposite is Stopped Down. Think of it as the retina in your eye. When you enter a dark room the retina in your eye gets larger akin to being Wide Open. When you step out into bright sunlight it gets smaller akin to Stopping Down.
Hopefully, all of this makes sense. This next part may be more difficult to understand. f/stop numbers increase as the aperture stops down. Whereas a 50mm f/2 lens is Wide Open at f/2, as the f/stop number increases the Aperture closes. The basic f/stops for this 50mm f/2 lens are f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22.
Over in the corner I can hear someone say, “I’ve got a 50mm lens, but it says f/1.4. What does that mean?” That means that your lens has an extra stop on the f/2 I have been using as an example. That means that your lens is Faster than mine.
Faster is another photographic term that describes a lens’s attributes. Generally speaking the Faster a lens is the better and nine times out of ten the more expensive. A Faster lens has a larger aperture. A larger aperture allows in more light. Remember your eye? In a darker room your retina gets bigger allowing more light in.
That means with the f/1.4’s larger aperture has a bigger retina. And with a bigger retina you have the ability to see in a darker environment. What difference does this make? On an average sunny day, none. In a low light situation, such as a concert, it can make all the difference in the world.
Hopefully this has been a helpful tutorial on lenses.
A few things to keep in mine when considering the purchase of a new lens. Whether you know it or not right now, a lower f/stop number is preferable. Faster is always better. And even though this equates to a more expensive lens, it is a good idea to remember that lenses hold their value long after your DSLR is selling for half of what you paid for it.
Next time I will discuss the effect a crop factor can have on your lenses.