Useful explaination for: What do numbers letters on digital camera lens mean.

What do numbers letters on digital camera lens mean

What do all the numbers and letters on a digital camera lens refer to and what do they mean?

If your new to DSLR photography the first things you'll need to know when buying a new lens will be concerning the numbers and letters printed on the lens. You will need to know what they mean to ensure you buy the lens that suits your specific needs.

DSLR digital camera lens

First I'll start explaining what the mm number means. For example on a Canon EF-S 17-85mm f/4-5.6 lens you will see the number 17-85mm written on the side. The mm number refers to the focal length. This is the length or distance from the front of the lens to the camera's sensor. The focal length is one of the most important considerations a photographer needs to take into account when buying a new lens. The mm number (distance in millimeters from the front of the lens to the sensor) will determine the style of photograph that can be taken.

For example, the smaller the mm number the wider the angle of view within a photograph. The photograph below looks to be a wide angle image. This is because it was taken with a 17mm focal length.

photograph with wide angle view

On the other end of the scale, big mm numbers like 200mm or 300mm provide a magnified telephoto view. They are good for animal photography where you might want to zoom in on a bird yet not be too close and scare it away. The photo below looks to be zoomed in closer as it was taken with a focal length of 300mm.

example of zoomed in photograph

The difference between a lens that has a single mm number to one that has two mm numbers.

If a lens has a single mm number, for example 100mm written on it, it is said to be a prime lens. This means the focal length of the lens is fixed and cannot be changed.

If a lens has two mm numbers on it, for example 17-85mm, this tells you it is a zoom lens. In other words it can take photographs with a 17mm focal length or zoom in all the way to a 85mm length.

What does the ratio number mean?

You might also notice a number written on your lens that looks like a ratio.
For example 1: 4 - 5.6

This number refers to the widest aperture available for that lens. The lens in the example above can be opened up to f/4 at the widest end (17mm) but only f/5.6 at the longest end (85mm). Generally speaking, the lower the f number the better, because in low light situations the lens can be used to give a brighter image.

Note also, the 1: part of the number is there purely because f stops or aperture is measured in ratio's.

What does Ø58mm mean?

If you see a number that starts with the character symbol Ø, for example Ø58mm written on your lens, it simply means that a screw on filter that is 58mm in diameter will fit this particular lens.

What does II USM mean?

If you have 11 (or ll as it's shown) written on your lens, this means it is the second version of that lens that the company has made.

USM means the lens has an autofocus motor type. To use autofocus you simply need to press the shutter button of your camera half way in and it will automatically focus.

What does the L mean?

If you have a Canon lens and it has a L written on it, this indicates that the lens is luxury series Canon lens. In other words they are the highest quality lenses that Canon manufacturers. You will also notice L series have a red ring around the lens as well.

We've decided to continue these tutorials on our photography website at: SLR Photography Guide.

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