Focal length numbers;I can't understand them and how they relate to distance from objects being photographed.

Answer 1

I'm not sure what you mean by focal length numbers. Let's assume you mean the lens length, i.e. 18-28mm. This is a wide-angle zoom. The numbers originally referred to the length of the lens. With new technologies, the lens can be shorter but still act like a longer, older version. So, we still use the numbers to refer to the characteristic of the lens.

A lens under 28mm is considered a wide angle. It will capture everything in the frame but pays particular attention to what is closest to the camera. Distant objects will appear smaller. A 24mm lens on a film camera is a nice wide angle. A 16mm lens is a nice wide-angle on a digital slr. The Digital SLR cameras have a smaller film plane and need smaller lens lengths.

A telephoto lens has a length above 70mm. A 70-210 will give you a nice variety of telephoto lengths. The larger the number the more powerful the telephoto. If you are shooting portraits, you'll want somethign around a 100-300mm. Once again, the 210 will be much stronger on a digital slr.

Answer 2

A lens with a long focal length will magnify the image, like looking through a telescope. A lens with a short focal length will give you less magnification.

There are two other major effects of focal length. First, the shorter focal length lenses have a wider field of vision. That means that you'll get more of what you're looking at into the photograph. Longer lenses cut off the image so you only get a small area.

The other effect is called "depth-of-field". A long focal length lens will only have a small region in focus. For example, objects 15 feet away from you may be in focus while those 14 or 16 feet away are not. With a shorter focal length lens objects from (say) 10 to 20 feet away may all be in focus.

You can use a small depth-of-field to your advantage to make the subject of your photograph stand out better from objects in the foreground and background. You've certainly seen photos of objects in front of a blurred background. Your snapshots (taken with a cheap camera with a deep depth-of-field) may have problems with objects in the background blending in with the object you're trying to photograph (the "tree growing out of his head" effect). A long lens can help you avoid that. So can getting as close as possible to the subject.

Answer 3

With a 35 Millimeter film camera, the 50 Millimeter Focal length lens is considered 'normal' because it most nearly mimics the focal length of the human eye... so what your camera 'sees' with a 50 mm lens is what your eye would see.

If you want to see farther, you need a telephoto lens... this may be anywhere from 80 MM to 5000 MM and, like a telescope, the longer the lens, the farther you can see. If you want to see more of the scene, you can opt for a wide angle lens. The usual is 35 MM but 28 MM lenses are common and then there is a whole variety of REALLY wide angle lenses.

All of this would be true for a digital camera but I'm not sure about to 50 Millimeter lens being the correct standard... most of the Digital cameras I've seen have a much shorter lens.

Answer 4

Some of my notes from the photography class I had this past semester:

Focal length = the distance from the lens to the film, is the most important characteristic of the lens and is usually expressed in mm. It determines the angle of view and the size of the objects in the image. The shorter (smaller) the f-length = the wider the view of a scene; the longer (larger) the f-length = the narrower the view.

Answer 5

Well, if you are asking about the "f" number, as in f1.4, f1.8, f2.0, f2.8 etc., a very simple rule of thumb is the smaller the number, the better the lens. So, you would find an f1.2 lens to be more expensive than an f1.8 lens. The absolute low number I have seen on a lens is f0.8 and this camera was capable of capturing high speed motion without using a flash light. Smaller numbers mean larger aperture - so more incident light - so being able to work in relative darkness.

Answer 6

The radius of curvature is two times the focal length. So: f=R/2 f=one hundred twenty cm/2 f=60 cm sparkling up for the area of the photo(di): a million/f = a million/do + a million/di di = fdo / (do-f) di = 60(20) / (20 - 60) di = 1200 / -40 di = - 30 cm sparkling up for the magnification(m): m = -di/do m = -(-30)/20 m = a million.5 ***the perspective of prevalence is an similar because the perspective of mirrored image. So the perspective of mirrored image is 40 six ranges too.

Answer 7

All the answers thus far are basically correct.

Lenses also have characteristics and flaws.

A "normal" lens varies with size of media. As pointed out 35mm full frame is 50 to 58mm. Wide angle for this is anything below 45mm and above 21mm. Telephoto is anything above 60mm.

For a digital camera (a non SLR) normal is about 8mm (50mm effective) and wide angle is 5.3 to 7mm (24 to 45mm effective). Telephoto is 9mm to 60mm (60mm to 400mm). This is for a 12x camera such as a Sony H2 or Cannon S2 or Kodak P850.

Wide angle and even "normal" lenses "bend" lines and cause perspective distortion, often known as the Pinnochio effect. If you get in real close to a person their nose is made longer by the lens in releaton to their eyes and ears.

This is how they shot the original Star Trek space ship, using a very wide lense to make the front of the ship huge and the back of the ship far and small and make it come into your face, SWWOSSH!

Wide angle is good for making "fun photos" like Carnival mirror photos where people are a bit distorted. THey are also good for scenic shots.

Wide angle lenses stay in focus from about 1 foot to infinity.

Telephoto lenses have what is called a "flat field" and thus a lense 75 to 105mm for 35mm cameras (9 to 10 mm for digitals) is considered a "portrait" lens because it makes the nose and ears keep the same persective. It also allows you to place your subject further away, maybe 6 to 10 feet for head shots.

Anything above 100mm is considered a telephoto and used to take distant shots of birds in trees, the moon at night, someone surfing in the ocean.

One the down side you pick up camera shake easier with telephoto lenses adn thus must shoot at speed above 1/60th hand held. Also the amount of light drops with "fixed" telephotos (not zooms) taht are very long. Finally, focus on these is critial and they generally won't focus closer than 3 feet and only 1 - 5 feet will be sharply in focus. Thus if you take a picture of someones face you need to make sure the nose and the ears are sharply in focus!

If you are shooting those surfers in the water you will have to readjust focus for each surfer at a different distance.

With a wide angle lens focusing is almost not necessary.

A normal lenses is rated for maximum amount of light (better than both fixed wide angle and telephoto lenses, better than zooms), very sharp images center to edges (telephoto drops off at the edges a lot, zooms drop off a lot) and a decenet flatness of field (there is still some Pinochio effect, but not as much, especially with a 55 or 58mm "normal" lens).

Today fixed lenses are almost extinct and almost everything is zoom, however for Canon and Nikon SLR (film and digital) you can get fixed wide, telephoto and normal lenses, although they generally come in a kit with a 35mm to 105mm zoom.

Most digital cameras have the eqilvalent of that same range with a 3 to 1 zoom lens (generally like 5.5mm to 16mm)

The F/stops another person talked about is that light gathering power. Zooms generally provide f/2.8 to f/3, while a fixed "normal" lens provides f/1.4 or f.1.8, which allows considerablly more light into the camera. Most fixed telephotos or long zooms are f/4 or f/5.6 which allow a lot less light inside.

f/ is the size of the front lens in mm divided by the focal length.

This is why longer zooms have bigger lenses, because to get more "f/" opening they need to have wider front elements. Smallers zooms (3x) don't need as wide a front lense.

A digital 60mm zoom needs a 30mm wide front lense to get you f/2 while a 15mm digital zoom needs only an 8mm wide lens to get you f/1.9 (which is almost f/2).

The difference between f1.4 and f/2 means you can shoot at 1/60th of a second at f/1.4 but if you maximum is f/2 then you must shoot at 1/30th to get the same amount of light and now you face camera shake. At f/2.8 you must shoot at a 1/15th of a second. At f/3.5 1/8th of a second.