What do the numbers on camera lenses mean?

SONY DSCIf your fairly new to using a DSLR then the numbers on the front and sides of the camera lens can be a bit confusing. It doesn’t have to be. we will explain to you what each set of numbers does or represents,and how this is important to you the amateur photographer, both for buying and using the lens. 

What lens are you looking at?
When you buy  a camera it usually comes with what is referred to as a kit lens. Depending on the  model and cost of the camera it can range from a so-so lens to a great piece of glass. Usually its the former. Which is why you see so many kit lenses for sale in pawn shops and on Ebay. Now there are some really great kit lenses out there that demand a princely sum even used. But that is another article.  SO regardless of what kind of lens your dealing with the numbers are all going to be very similar in nature and layout.

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Lets start with the front of the lens and interpret the writing located in a circular pattern around the front of the glass. There are usually between 2 and three different pieces of information on the front of the lens. In addition to the name on many lenses you will find the aperture sizes of the lens, the F-stop range, and the filter ring size. You may also find model number and the country of manufacture on some models.

  1. Filter ring size This number usually with the symbol 0 with a slash through it signifies the size of the filter mounting ring threads on the front of the camera. In the case of the image at the right, the filters for this lens either need to be 55mm in diameter or utilize a 55mm to whatever size adapter ring. This measurement also applies to the size of lens cap you need for your lens should you ever lose the original cap. If you by lenses of the same filter ring size, then you only need to keep one set of filters on hand for any situation. This is rather hard to do but it can be done.
  2. Minimum Focus Distance This measurement signifies the minimum distance the photographer must stand from the subject to achieve good focus. This is often confusing because everyone assumes the minimum focus distance is from the front of the lens. This is incorrect. the MFD is actually from the focal SONY DSCplane line mark on the body of your DSLR. This is usually located towards the back edge of the body as shown on the Sony body to the left. In this case of this lens the MFD is .25m/.82ft. So around a quarter of a meter or 10 inches.  The longer the lens the further out this distance is going to be.
  3. 3. Aperture and Focal length – These are possibly the most important numbers on the lens. Sometimes very rarely they may SONY DSCnot be located on the front of the lens, and may only be on the side of the lens like the image to the right.

3-1 Crop or full frame? In the case of the Sony lens to the right the series of numbers is preceded by DT, which signifies it is a Sony lens designed for Crop Sensor cameras. So it would not work well on a full frame camera. Nikon has Dx  and Cannons has EF-S all signifying the same thing.  You may or may not have preceding letters on your lens. This is a fairly recent addition to lens lineups. Older lenses will not have this sort of identification. Another recent addition is the inclusion of motor ID tags. in this case SAM signifies Sony’s (Smooth Auto-focus Motor). Which says it is a cheaper motor than some.

3-2 F-stop or Aperture range – Following this on the two examples in the pictures to the right are the f-stop capabilities of the lens.  In the Sony 55-200mm at the right we have 4-5.6, which signifies that this lens has a varying f-stop or Aperture range of f4 to f5.6. The 18-55mm lens has an f-stop or aperture value of f3.5 to f.5.6. This equates pretty easy. On the 18-55mm it is f-3.5 at the 18mm or short end and at f-5.6 at the 55mm or long end of the focal length. This value will change almost equally across the entire focal range.  These two lenses are equal (f5.6) on the long or telephoto end but the 18-55 has a slightly faster aperture on the short end of f3.5. More on that later.

3-3 Focal length – Next on the lenses after the / is the actual telephoto or focal length of these lenses. If your dealing with a prime lens then you will only have one number. In the case of a telephoto your going to have 2 values separated by a dash. In the two examples shown here we have an 18-55mm telephoto on top and a 55-200mm telephoto on the bottom. These values tell you what type of lens your dealing with. For example a ‘Normal’ lens is considered 50mm, which is just about the focal length of view your eyes give you. A Wide lens is anything below the 50mm mark. these give you wider angles of view than what the normal eye sees. Almost as much a 180 deg in some cases. Telephoto  lenses are any lenses above 50mm that bring the subject closer to the camera. Many photographers have a ‘Goto’ lens they use that covers a fairly wide range of shooting scenarios. A 24-210mm would be one example. The faster, or smaller the aperture the better as well.

SONY DSCThe Side of the lens.

On the side of the lens you will probably find a repeat of the same information that is located on the front of the lens. Aperture, focal length, filter size and sometimes the manufacturers names. But there is other information that if used correctly can be very helpful to you as a photographer. That being said, newer lenses are inherently being shipped with less and less information located on the outside of the camera lens. With the advent of the digital camera age, the information from the lens in being display digitally either on the lcd live-view screen or in the viewfinder. Relegating the writing on the lens itself redundant and non essential. So you may or may not see some of this info on your lenses. But if you’re like me and on the look out for older glass in pawn shops and thrift stores, then your going to want to pay attention to it. I find older lenses very nice to use. I can set my focal lengths and sometimes aperture, depending on the body, before I ever look at the back of the camera.

Focal length markings – When you zoom in and out with a telephoto lens, the camera may or may not tell you how far you focal

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length is in or out. The image at the left gives you a quick reference on what focal length your shooting just in case. This image is with the lens completely zoomed in to 55mm. The image to the right is of the same style of markings on a small  lens that shows the lens is at about 26mm.

AF/MF Switch – Next to the focal length reading is a switch labeled AF and MF. This switch gives you the ability to turn off the auto focus ability of your camera with out entering the menus. This is very handy if your camera doesn’t have a switch on the body for this function or if you want to enter manual focus in a hurry for those times when auto-focus is preventing you from getting the shot.

So what does it all mean? – If you  take the information you find on the lens, your going to be able to determine if the lens is capable of getting the shot your looking for before you ever put it onto a camera body.

  • The aperture or f-stop reading tells you the amount of light that the lens will let in and how fast the lens is. Fast in lens talk means how quick a lot of light can be let into the lens. This allows for shorter shutter speed times and the ability to stop faster moving objects with more light ability. The smaller the f stop number, the faster the lens. A lens really doesn’t get spoken of as being fast until it the f-stop is somewhere below the 3.0 number. f2.8 is fast, f1.8 is faster, and f1.2 to f1.4 are amazingly fast. As you may guess. the faster the lens, the higher the price tag in most cases.
  • The Focal length of the lens determines how far out the lens will zoom to bring the distant objects closer to you. The smaller the focal length the less magnification and the wider the viewing angle. using the lenses here, the 18-55 is a telephoto lens that opens up from a Wide 18mm to a 55mm tele lens. This general purpose lens will take  images that are very wide angles of views at 18mm up to 55mm which is about what the human eye sees at. The 55mm to 200mm with take over from there and also be able to zoom in on objects far away using the 200mm setting.

Taking the information you find here can help you make an educated purchase of a lens that will complement your photographic arsenal. I see all too often people carrying around duplicate or cross over lenses in their camera bag that they just don’t need. using these numbers we should be able to narrow it down to a couple of lenses to take with us for just about any situation. Many times I am able to take only one lens and get every shot I am looking for.

Good luck and keep shooting Str8.

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Is an amateur photographer and writer who enjoys sharing information with others. "Technical information sharing is a critical part of helping everyone become a better photographer. If you don't know it, you can't do it!" From Film to Digital, photography has changed a lot, but the idea of learning hasn't.

One comment on “What do the numbers on camera lenses mean?

  1. Nick says:

    Great article, man! Thanks!

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