It's good to know something about lenses when choosing a digital camera, because the lens is arguably the most important part.

I'll quickly outline some things to consider and will go into more detail below. The extra detail is more advanced information and while informative, not absolutely necessary.

The information below is basically the same as in the course.

When you have a look at a camera's Specifications, you'll see information like this about the lens.

What does all this mean?!

Focal Length (optical)
The (W) means Wide (no zoom) and the (T) means Telephoto (zoomed in).

The second measurement (T) simply shows the size of the zoom.

It's giving you information about both - but why?

The first line is the actual size of the lens and the second line, "35mm film equivalent" is a guide. This guide is important.

35mm film equivalent
"35 (W)" is highlighted to show that this camera is equivalent to 35mm in wide view.

Maximum Aperture
The last line, Maxiumum Aperture, tells how "bright" the lens is. It refers to how easily light gets through and how wide the opening is.

f/2.8, like this one is quite average, although some lenses go right down to f/1.2 which is very "bright."

f/4.8, shown at the zoom (T) range, means that when zoomed in the picture will get darker because less light is getting through.

This darkening, depending on how little light gets through (or how high that number is), means that you or the camera has to try and make up for it.

This could lead to grainier or more blurry photos as the image is brightened up artifically.

This will happen either automatically by the camera or manually by the user, either way, it's a sign that you're more likely to need a tripod when zooming, or the camera should have an Image Stabilizer built in to help with the picture quality.

How to interpret what is written on the lens
The lens has the same information that's given in the specifications, except for the film equivalent part.

On the lens you'll see numbers like in this example:

The lens will always have 2 sets of numbers written on it.

The numbers are always a range from normal to full zoom.

The second range of numbers (1:2.7-3.5) lets you know how "bright" the lens is, so now you have a better idea of what the image would be like without seeing the Specifications any actual photos!

Just remember for the second range of numbers, the lower the better.

This next part is a little more technical so skip ahead if you like...

How to judge the quality - Brightness
The lens can be judged for quality in a number of different ways.

As mentioned, one of the ways is by how "bright" it is (or "fast" it is in photographer terms). This is given a rating in F stops. The average is 2.6, or f/2.6.

Some cameras are higher than that, meaning that it will need to artificially compensate for the loss of light. The camera has to either slow down the shutter which leads to blurring, or more noise and grain builds up when the ISO is set higher as it tries to brighten the photo as it's taken.

How to judge the quality - Engineering
This is something that only actual tests, your own use, or reviews will reveal. This kind of information is not accurately given by any manufacturer. But knowing a little about it beforehand can help you understand the information given by review or test sites.

Another area of judgement of the lens is its edges. There are 3 things that can happen at the edge and show up in your photos, although it's quite slight. The first is a slight darkening of the corners where less light can get through, the second is blurring, and the third is called Distortion (the image bends slightly.)

Another thing to look for is colour fringes on the edges of bright objects in the photo, which is called "Chromatic Aberration." This shows up in high contrast areas, such as tree branches and leaves where the sky shines through giving the edges a bright blue colour, or on bright narrow objects which can give a red halo look. The occurs mostly at full zoom.

Chromatic Aberration on the antenna, and other bright areas.
Notice the red glow on the top and blue glow on the bottom.

The good news of all of this is that it's not very common in point-and-shoot cameras or with low zoom, but they start to become more noticable on high zoom consumer cameras where there is alot more involved in the lens system, and where manufacturer costs increase dramatically to produce better quality, which is often out of reach for most users.

Now you may begin to realise why Digital SLR Cameras are so much more expensive than similar cheaper models, even when the SLR may have less megapixels etc. The cost is mostly the lens, and sometimes an SLR will be sold without one!

I included this information on lenses to help with an understanding on how to choose a digital camera that is most suitable for you. If you already have a camera it will help to weigh up a good future camera when you begin to become more confident and creative in photo shooting.