There was an error in this gadget

Monday, June 10, 2013

What the Numbers on your Lens Mean

What the Numbers on your Lens Mean:
Some things seems pretty straight forward and like they’re common knowledge, but I’ve run into this a few times with my students that feel embarrassed to ask what all the numbers on the lens mean. There is no reason to feel stupid or embarrassed if you don’t know this, it is sometimes confusing. So I’m going to run through them one by one.

Common settings seen on newer digital lenses

FOCAL LENGTH

If you have a zoom lens you will have a ring that turns to zoom in and out and it will also indicate what focal length you are currently set to. For example of your lens is a 70-200mm like mine you may see this which indicates I’m at 100mm currently.
focal-length-600px
If you are using a prime or fixed lens you won’t have a zoom ring, it will simply indicate the focal length on the lens barrell, as you see on my 85mm lens below.
focal-length85mm-600px

MAXIMUM APERTURE

The maximum aperture is the largest opening (the smallest number) on the aperture scale that your lens is capable of opening to.  Larger apertures like f2.8 or even f1.8 are highly desirable because they let in more light and allow you to shoot in low light conditions without getting camera shake.  (for more on that read 5 Tips for getting sharper images or Why the 50mm lens is your new best friend) This will vary from lens to lens and you may actually see a range of numbers such as 3.5-6.3.
You can usually find this information in one of two places on your lens, or perhaps even in both places:
  1. right on the end of the lens barrel on the edge
  2. on the front of the lens inside the filter ring area.
In the example below you can see two different lenses.  My Tamron 17-35mm (notice the focal length range is shown there also) and my 85mm. On the Tamron you see “1:2.8-4″ and on the 85mm you see “1:1.8″.   What that means is that the maximum aperture on the 85mm lens is f1.8, but on the Tamron zoom it changes from f2.8 to f4 as you zoom the lens.  At the lenses widest, 17mm, I can open the aperture to f2.8, but if I zoom all the way in to 35mm now my maximum aperture is only f4. This is pretty common with kit lenses and ones that have a large focal length range such as 28-300mm or 18-200mm.
maximum-aperture-600px

FOCUSING RANGE AND DISTANCE SCALE

Some lenses, not all digital ones have this now, you will see a range of distances – usually marked in two scales, feet and meters. Look for the infinity symbol at one end, the other end will show how close your lens can focus, or its minimum focusing distance. Some lenses have built in MACRO settings which allow you to get a bit closer. They aren’t a true macro and you can’t get in super close but it’s a handy thing to have if you want to get closer without the expense and weight of an extra lens.
In the two lenses below you can see the scale on the Tamron (on the right) is in the outside of the lens and on the Canon 70-200 you can see it inside under a cover. Both will move if you manually focus your lens (**note: please remember to turn off auto focus if you do this because turning the focusing ring while autofocus is on can damage the gears and mechanisms inside your lens**)
focus-ring-distance-600px

FILTER SIZE OR LENS DIAMETER

Also on the end of your lens you may see a funny symbol that looks like a zero with a strike through it, then a number.  That indicates the diameter of the front of your lens or the size of filter required to fit on it. You can also find that same number on the back side the lens cap, see below – for this lens it is 77mm. Handy to know if you want to go to the camera store to buy a filter, or you’re buying something online.
filter-size-600px

Less common settings often seen on older manual focus lenses

APERTURE RING

This is one that you may or may not have on your lens, most newer digital lens do not have this as the aperture is set and controlled by the camera body now. Back in the days of film and manual focus lenses, the shutter speed was set on the camera and the aperture was set on the lens. You can pick up some great deals on older film lenses for specialty uses like macro, or fixed lenses with large apertures often for a fraction of the price of a new digital lens (you just need to get a special mount adapter ring to attach them to your camera). Just be aware that they will be manual focus and some of them you have to set the aperture on the actual lens itself. If you have one of these it may look something like either of the ones below:

HYPER-FOCAL DISTANCE SCALE

This is a bit of a trickier one to find and explain. If you have all zoom lenses, you will not find this on your lens. If you have a prime lens, especially an older model you may see an extra ring of numbers on your lens such as in the image below (the numbers in the middle radiating out from the central orange line).
The numbers on the lens above represent (in order from top to bottom ring)
  • the distance scale
  • the hyperfocal distance scale
  • the aperture ring that actually sets the lens aperture
You use the hyperfocal distance scale to know which parts of your image will be in focus at different aperture settings. Notice the lens above is set to f16 and it is focused at 5m (15 ft). Now look at the middle scale and go to f16 on the left side of the orange line – that is indicating the closest point that will be sharp when focused at that distance, using that aperture – in this case it looks like about 2.75m (approx. 9ft). Now look at the f16 on the right of the orange line and you see it’s at infinity. So what we can tell from this is that at f16 we can get from about 9ft to infinity in focus, but the trick is to focus in the right spot.
Using the hyperfocal distance scale you’d actually put the infinity mark at the f16 mark on the right and that will give you the most depth of field possible at f16 (notice you don’t actually focus ON something, you set it on the lens by the numbers).  Note:  if you focused on infinity you’d only get from about 15ft to infinity in focus (estimating here) or if you focused at 7ft you would not get infinity sharp.  There’s a bit more to it than that but if you pick up a lens that has such a ring – do some research on how to use it and you’ll get a lot more of out of your small apertures.
If you’re curious what the little red dot means, that’s the infrared focusing mark. When shooting with infrared film you actually had to focus at a different place  than normal because the infrared spectrum of light is different than what we see with our eyes.  I used to shoot infrared film now and then, fun stuff, but tricky to handle, focus and you need to know what you’re doing with it.  There’s now ways to replicate fairly closely that same look digitally, even though now and again I think about shooting some film.
That’s it for lens numbers (I hope!) if I missed anything let me know.  Share a photo of your lens and any numbers you can’t decipher and if I don’t know what it means I can try and find out for you, or maybe someone else can help out in the comments section.

Post originally from: Digital Photography Tips.



Check out our more Photography Tips at Photography Tips for Beginners, Portrait Photography Tips and Wedding Photography Tips.

What the Numbers on your Lens Mean