Can somebody explain the difference in camera lenses and what all those numbers mean?

Question

I am in the market for a lens for me newly purchased DSLR--specifically a Nikon D40X. I don't know that much about lenses or which kinds you need to take certain types of pictures. So I would really like to know just exactly what all those numbers mean. 55-200mm ??? Thanks for all your help!!


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Answer 1

Think of a camera lens as a pipe with glass. First the diameter of the pipe allows either a little or a lot of light to pass through depending on that diameter. The length of the pipe determines if it is wide angle, normal, or telephoto. The glass inside this pipe allows the pipe to focus from infinity to a close focus depending on the configuration of the glass inside the pipe. So, in your case, you have a "pipe" that is variable from 55mm, normal, to 200mm, telephoto. All lenses are only their stated length when the lens is set to the infinity symbol ∞ on the focusing ring. Also, there are other numbers called ƒ-stops which control the amount of light going into the pipe onto either the film or a digital sensor. An ƒ-stop is merely a fraction of the hole in the aperture divided into the length of the pipe (focal length). So, a lens that is say 200mm with an ƒ4.0 lens has an opening 200÷4=50. That lens has a maximum opening of 50mm across. That same lens set at ƒ11 produces an opening of 200÷11=18.18mm across. In photography, we only use one number -- 2. Either by multiplying and dividing with it for the shutter speed, or using the square root of 2 for anything to do with area -- such as the aperture. This is why ƒ-stops are 1.4 - 2.0 - 2.8 - 4.0 - 5.6 - 8 - 11 - 16 - 22 - 32. They are all multiples of the square root of the number 2 which equals 1.414. The difference between an 8x10 sheet of photo paper and an 11x14 is the square root of 2 -- 1.414. Multiply each side by the square root of 2. If you are making your own set of prints and you want to enlarge the full image from an 8x10 size to an 11x14 print -- just either double the time of exposure or increase the enlarger lens aperture by one full stop. Last, in 35mm cameras, anything shorter then 50mm is called wide angle, and everything longer then 50mm is telephoto. The "normal" lens for 35mm is considered to be a 50mm lens, but technically it is really a 43mm lens. It is based on the Pythagorean Theorem -- (A)squared + (B)squared = (C)squared with "C" being the hypotenuse or the length of a normal lens for any format camera. Sorry to bore you, but once you hear this -- just store it away somewhere in the recesses of you mind, and just make nice wonderful pictures for yourself -- have fun.

Answer 2

Explain Camera Lenses

Answer 3

There's two main sets of numbers to remember:
1) focal length (focal lengths for zoom lenses)
and
2) maximum aperture (the size of the widest lens opening, which can vary slightly for zooms).

Let's start with focal lengths, which are a measure of how strong your lens is for wideness or telephoto. It allows you to make some relative comparisons between lenses. So, for example, let's say you have an 18-55mm lens. 18mm is fairly wide, while 55mm is a very moderate telephoto. By comparison, a 55-200mm lens goes from a moderate telephoto to a long telephoto.

Those are zoom lenses, which cover a range of focal lengths, like 18-55mm or 55-200mm. Because they can change magnification, ie going from wide to telephoto, they can "zoom" and thus are called zoom lenses. Sometimes, people will talk about a zoom ratio. That's easy to figure out--just take the big number and divide by the smaller number. So the 18-55mm zoom is 55/18 or a 3x zoom. Likewise, the 55-200mm is 200/55 or a 3.6x zoom.

You can also compare lenses: 200/18 or at the 200mm telephoto extension, it is 11x stronger than the other lens at its widest 18mm setting.

Now, what about the aperture or lens opening, sometimes called an f-number or f-stop? Lenses are measured also by how well they let light in. The more light it lets in at the widest aperture, the more expensive the lens is likely to be. You'll see f-numbers like f/2.8, f/3.5, f/4, f/5.6, etc. On zooms, this can vary, so you may see things like f/4.5-5.6.

What this measures is how much light comes in when the lens is at its widest aperture or "wide open." On a zoom, the first number corresponds to the zoom at the wide end; the other number to the zoom at the telephoto (or less wide) end. This is known as a variable aperture zoom.

In dim light, you'll want a lens with a maximum aperture of like f/2.8 or better (smaller number = bigger lens opening) if you want to shoot available light. However, if you shoot with flash, this becomes less critical, which is where consumer level lenses come in. Professionals prefer the wide aperture lenses for a variety of reasons, despite their huge cost.

Aperture affects things like "depth of field" -- the area in focus, which is a whole 'nother discussion entirely.

Answer 4

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Answer 5

I forget exactly what the numbers measure, but it has something to do with the curvature of the lens and, hense their ability to magnify an image. For all intents and purposes, the numbers define the focal length. Lenses labeled 50-55 mm are "normal" and focus at about 6 feet and are OK for most pictures regular people normally take. Numbers much smaller than that (say 25-30 mm) are considered "close-up" lenses, sometimes called Macro lenses. Much above 60 mm and you're talking "telephoto" lenses and the bigger the number the farther away you can focus on objects. The physical lengths of the lenses are inversely proportional to the "size" with close-up lenses being distinctly shorter than regular lenses, which are shorter than telephoto lenses.

Answer 6

The mm numbers indicate the coverage angle of the lens, and with a fuctuating number range of 55-200mm this is indicative of a telephoto lens. Wide angle lens (in the 28mm range on a standard SLR) are suitable for panoramic views of landscapes, whereas 49mm or 50mm lenses are suitable for portraiture work and subjects that are relatively close. These are basic rules of thumb for standard (film-basd) photography; the rules may be slightly different for digital applications, so be prepared to consult books on the subject before making a purchase. *If it helps you to know this, Nikon optics are among some of the best in the industry, worldwide.

Answer 7

Liz your best bet is to find some Groups on the internet and read their threads relating to lenses

there is a wealth of information on the net

Avoid Ken Rockwell he often does reports on equipment he has never touched. he also posts stuff on his website which is pure trash because he finds it humerous.

this Url should get you some good groups

http://www.flickr.com/search/groups/?w=all&q=D40&m=names

there are also some good groups on Yahoo in particular
Nikon Lenses but it is more for the experienced amateur instead of beginner level

Good shooting

Mike

Answer 8

Thank you for the replies, very much appreciated!