Skip to main content

What do the numbers mean on a camera lens?

Lens Basics


Lenses don't have fun names, but rather are labeled like this: 18-55mm f/3.5-5.6. That designation tells you a lot, but doesn't mean much if you don't know a few terms. 


IS = image stabilization - an electro mechanical system in the lens that counteracts camera shake.

USM = Ultrasonic Motor - refers to the focusing motor in the lens. USM lenses focus faster.






Zoom Lenses vs. Prime Lenses

Zooming Lens
 A zoom lens does what you might expect: it zooms in and out, allowing you to magnify your subject. A prime lens can't zoom. If you want to move closer or farther away with a prime, you move your legs rather than turning a zoom ring on the barrel (i.e. the body) of the lens. Why would anyone prefer a prime to a zoom? Primes are often cheaper, offer sharper results, have wider apertures (which means they can take in more light, thus performing better in low light situations), and generally handle their specific function better than a zoom. That said, for enough money a zoom can perform just as well and offers more versatility. Obviously you have an advantage if you don't have to

Prime Lense
constantly change lenses. Zooms allow you to essentially change the lens, and therefore the type of shot you're getting, by zooming in or out. Primes do not.
 
Both zoom and prime lenses are designated by their focal length. Focal length is often measured in millimeters (mm) and designates the distance at which something is in focus. This definition doesn't mean much practically speaking, so what you want to remember about focal distance is that lower numbers indicate a wider view (zoomed out) and larger numbers indicate a closer view (zoomed in). 
For example, if you're photographing a small room in a house and you used an 18mm lens you'd likely capture the majority of the room in your image and you'd get very little of the room with an 85mm lens. Primes only have one focal length, and so they're simply labeled as 35mm, 50mm, and so on. Zooms offer a range, and so they're labeled as 18-55, indicating that you can achieve a focal length as wide as 18mm, as close as 55mm, and everything in between.

Aperture


Lens titles have two measurements. The first is focal length, as we just discussed, and the second is aperture. Aperture determines how much light your lens can let in. When a lens has a wide aperture, designated by a small number called an f-stop (e.g. f/1.8), it captures more light. When a lens has a narrow aperture, designated by a larger number (e.g. f/5.6), it captures less. Wide apertures allow you to take photos when less light is available because the lens can see more of the light. Take a look at the photo to the right. The pictured lens current has a wide aperture, and you can see a lot of light passing through the front glass of the lens straight through the back. If that hole were smaller, the aperture would be narrower and less light could pass through. Aperture isn't just a concept, but something you can actually see when you look at a lens.
You're not stuck with a single aperture. When a lens is rated a nice, wide aperture like f/1.8 that just designates its maximum. You can change the aperture on your camera to a narrower aperture to allow less light. Why would you do this? Narrower apertures provide a greater depth of field, meaning that more of the image will be in focus. When you're photographing a landscape, you want the entire image to be in focus and not just the part of the plane that your camera focused on. A higher, narrower aperture (e.g. f/12) provides that. A wider aperture (e.g. f/2.8) would make the landscape appear less sharp. That said, you don't always want everything in focus. When taking a portrait, for example, wide apertures are wonderful because you can focus on a person and allow the background to blur away. As demonstrated in the example photo to the above right, the only things in focus are the aperture blades of the lens. A wider aperture made this possible.











Comments

Post a Comment

Popular posts from this blog

Single-lens reflex camera

A   single-lens reflex camera  ( SLR ) is a  camera  that typically uses a mirror and prism system (hence "reflex" from the mirror's reflection) that permits the photographer to view through the lens and see exactly what will be captured.  With  twin lens reflex  and  rangefinder cameras , the viewed image could be significantly different from the final image. When the shutter button is pressed on a mechanical SLR, the mirror flips out of the light path, allowing light to pass through to the light receptor and the image to be captured. Who created the SLR camera? Thomas Sutton The photographic single-lens reflex camera (SLR) was invented in 1861 by Thomas Sutton, a photography author and camera inventor who ran a photography related company together with Louis Désiré Blanquart-Evrard on Jersey. Only a few of his SLR's were made. Louis Désiré Blanquart-Evrard What is meant by SLR camera? A single-le
Post a Comment
Read more

Construction of simple lenses

Most lenses are  spherical lenses : their two surfaces are parts of the surfaces of spheres. Each surface can be  convex (bulging outwards from the lens),  concave  (depressed into the lens), or  planar  (flat). The line joining the centres of the spheres making up the lens surfaces is called the  axis  of the lens. Typically the lens axis passes through the physical centre of the lens, because of the way they are manufactured. Lenses may be cut or ground after manufacturing to give them a different shape or size. The lens axis may then not pass through the physical centre of the lens. Toric or sphero-cylindrical lenses have surfaces with two different radii of curvature in two orthogonal planes. They have a different focal power in different meridians. This forms an astigmatic lens. An example is eyeglass lenses that are used to correct astigmatism in someone's eye. More complex are aspheric lenses. These are lenses where one or both surfaces have a shape that is neither sp
Post a Comment
Read more

How digital cameras work

How digital cameras work? Digital cameras look very much like ordinary film cameras but they work in a completely different way.  When you press the button to take a photograph with a digital camera, an aperture opens at the front of the camera and light streams in through the lens. So far, it's just the same as a film camera.  From this point on, however, everything is different. There is no film in a digital camera. Instead, there is a piece of electronic equipment that captures the incoming light rays and turns them into electrical signals. This light detector is one of two types, either a  charge-coupled device (CCD)  or a  CMOS image sensor . Notes:    An   image sensor   or   imaging sensor   is a   sensor   that detects and conveys the   information   that constitutes an   image . It does so by converting the variable   attenuation   of light   waves   (as they   pass through   or   reflect off   objects) into   signals , small bursts
Post a Comment
Read more