Understanding camera lens, for beginners

AF-S 14-24mm f/2.8G IF-ED, AF-S DX 18-55mm f/3.5-5.6G VR, AF-S 18-200mm f/3.5-5.6G DX VR IF-ED, Tamron 70-300mm f/4-5.6 AF Di LD Macro, AF-S 50mm f/1.4G, 300-800 f/5.6 APO EX DG HSM

You may be wondering what’s all those stuff mean! Don’t worry! Today I am back with an article, aimed to help you understand stuff related to lens, in simple and easy words 😛

A small note :
Photography is only a hobby for me. I will try to explain a few things I have been learning since the last months. Feel free to share your own experience. This blog post is aimed to newbies only… You may want to read a previous article in which I introduced photography in a few words…

What is a lens?

The wikipedia definition goes as follows :
“A photographic lens (also known as objective lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.”

You don’t need to learn this by heart. You can skip the definition, it won’t be of much use to you right now.

What you need to know…

You have surely noticed the “14-24mm” or “18-55mm” or “70-300mm” in the first line of this post. Well, these are known as the focal range of the lens.

Before going any further, you need to understand the following, I need to mention that for the sake of simplicity, I won’t be taking the 35mm or crop factors into consideration. I need to document myself more in depth before being able to explain these parts to you. But you should note that these are widely used terms in photography.

Let’s see a few images, all at the same location (from La Citadelle, Port Louis) but shot at different focal length.

Typically, the optical zoom of a lens is calculated as follows :

Optical zoom = maximum focal length / minimum focal length

Example of lens :

• AF-S DX 18-55mm f/3.5-5.6G VR
  Zoom = 55/18 = approx 3.0x
• Tamron 70-300mm f/4-5.6 AF Di LD Macro
  Zoom = 300/70 = approx 4.2x

Zoom, focus, aren’t they the same thing?

There is a difference between the 2 words.

You normally zoom to have a larger image of what you are shooting. This is done by extending the focal length of the lens by turning the zoom ring on the lens to make it longer. Beware, we are talking about optical zoom here, not digital zoom. In short, digital zoom is a processing done by the camera to enlarge the picture as it is. At the end, you may end up with a picture, full of small squares(pixels).

[image from http://photo.net/equipment/digital/basics/ ]

On the other hand, focusing allows you to select a point or a region of what you will be shooting. It is a bit difficult to explain it in words. The following images will help you to get a better idea :

“3.5-5.6G”, what do they really stand for?

Good question…

That’s the maximum aperture that can be obtained using this lens. The aperture is a measurement to denote how large is the opening of the lens, hence the amount of light that can enter.

For this specific example ( AF-S DX 18-55mm f/3.5-5.6G VR), a maximum aperture of 3.5 can be obtained at the lowest focal lenght, i.e. 18mm and a maximum aperture of 5.6 at the end, 55mm.

Understanding aperture can be a bit confusing. Let’s see how…

[aperture diagram from here ]

A large aperture number (ex. f11) refers to a SMALL opening of the lens (allowing little light in) and a small aperture number (ex f3.5) refers to a LARGE opening (allowing more light in).

Only one aperture marking?

Some lenses have only 1 aperture, take the following lens as example : AF–S NIKKOR 24–70mm f/2.8G ED.

Well, this lens have the same minimum aperture of 2.8G over the whole focal length. Please note that these lenses are generally much more expensive.

Only one focal length(mm)?

No, they did not forget to print the other ‘mm’ value. In fact, these type of lenses are called prime lenses. They offer only a fixed focal length, for example 35mm or 50mm. You can’t zoom with this lens because of the fixed focal length. However the image is of much better quality and they focus more quickly, even in low light conditions.

Example : AF-S 50mm f/1.4G

Because of the larger aperture(smaller number), this lens will be able collect more light than a lens with an aperture range of 3.5-5.6, hence produce better images even in low light.

Built in motor into lens / body motor

Once again, a simple explanation : A motor is necessary to move the lens elements in order to vary the focal length, hence the zoom. As written above, the motor can either be in the body of the camera itself or into the lens. We often talk about auto focus motor lens in the second case.

Nikon examples

• without a motor in the body : D40, D60, D3000 and the D5000.
• with a motor in the body : D80, D90

A lens for a D80 will work on a D5000 but due to that lack of a motor in the body (of the D5000), the auto focus will not work. Hence, the person needs to manually use the focus ring when taking pictures. Older lenses did not have any motors, hence the D80 has a wider choice of lenses for use, while the D5000 is restricted to newer lenses only.

Please bear in mind that a lens designed for one make of cameras cannot be used on another make. We are here talking about the mount, which basically allows a lens to fit into a specific camera. However, there exists adapters which can be used.

I hope that this article helped you to have a better understanding of lenses used in digital photography and some of the terms used in this field.

Feel free to ask any questions and also, don’t hesitate to share your experience. And of course, please leave any comments if I made errors in the article above.

Other images from

• http://kenrockwell.com/
• http://digicam-print.com/digital-camera-lenses/