Lenses

A comment by one of our readers Shani prompted this post. A question was asked:

Could you please share some info regarding the different lenses.

Now, lenses cover a huge area and can be quite technical when it comes to saying why one lens might be better than another. Plus there are lots of manufacturers of lenses, some will be available for some makes of cameras, others won’t so that adds extra complications.

If you want to find out how a camera lens is made, then I found this page which explains it.

So to start with, what are the different types of lenses. Well the two main types are prime or zoom lenses.

Prime Lenses

These are a fixed focal length, so there’s no zooming in and out with these. They are often a better quality lens optically than a zoom of similar length, and can quite often be expensive to buy due to the higher quality.

So why would you want a fixed focal length lens? Doesn’t that make it more restrictive?

Well, yes, it is more restrictive as you have to physically move to frame your picture, but the improvements in image quality and the reduced weight (usually) of a prime lens over a zoom make it worth while.

Zoom Lenses

These are lenses that give you a range of focal lengths. The term zoom lens doesn’t always mean you will be able to magnify the image, as you can get wide angle zooms with very short focal lengths, only a telephoto zoom will allow you ‘bring the subject closer’. So I guess that could be a third type, telephoto.

f numbers

A lens will have an f number. For a prime lens you will get a single f number, whereas a zoom lens may give you a range of f numbers, but it can still have a single f number. This f number is the maximum aperture you can use, as in the widest hole you can set of light to get in. When you buy your camera you may get a kit lens with it, usually a zoom lens. Let’s say with your shiny new DSLR you get an 18-75mm zoom lens. This means that the lens will go from 18mm to 75mm which is a good range for starters.  On this lens you may see it has something like f3.5-5.6 on it too. This is the aperture range that lens has and means that when the focal length is set to 18mm you will be able to use a maximum aperture (f number) of 3.5 but when you use the 75mm focal length you will only be able to use a maximum aperture of 5.6.

So what makes a lens a good one?

There are various factors which make lenses thought of as good. First off, and most importantly, will be optical quality. As the glass used in a lens is not flat, all sorts of problems can occur such as distortion when light passes through it.

This is when the image gets distorted in an unnatural way. Or certain portions of the image appear more distorted than others, usually nearer the edges. I won’t bore you with all the technical details of distortion (mainly because I don’t know them), but the better lenses have less distortion present, resulting in a better image. Better quality glass also produces better colour in your images, and will reduce the chance of getting a nasty lens flare in your image.

A better lens will be one that is able to focus on the subject quickly. At the cheaper end of the scale, lenses can take a while to focus on a subject and will often ‘hunt’ to find a focal point. Hunting is the term used when you see the lens going backwards a forwards several times until it finds something to lock onto. With the higher spec lenses, you usually get a wider aperture (smaller f number) which allows more light into the lens while it’s focussing and therefore helps the lens focus quicker. That is why you see all these sports photographers or nature photographers using these big expensive lenses. They need to be big to help get that wide aperture so they focus on the subject quickly, very important for the sports or wildlife.

So should I buy the cheapest lens I can find or save my pennies?

Well, for lenses, the saying ‘you get what you pay for’ is certainly applicable. You may think that buying a cheap lens that gives you a nice long focal length to get things nice and close is a good idea. I’m not saying don’t buy the cheap ones, you just need to know the limitations of that lens. If it’s all you can afford then that is what you’ll have to get. It may be very slow to use, as in slow to find it’s focal point, it may be made of cheap materials and may not stand up to knocks or the internals may prove problematic after some time, or the optical quality may be poor.

If you think about it, you tend to change your lenses less than you change the camera body, so it pays to save up and buy the absolute best lens you can afford. If you are getting a new camera and a lens, consider getting a slightly less expensive camera and spend more on a better quality lens, the rewards of having good glass are much more than having all the latest gadgets on the camera body.

Now the subject of lenses is a big one. I will try and sort some images out that explains some of the good and bad points about lenses so you can see for yourself what the differences maybe.

If you are considering buying a new lens to add to your kit lens to give more range or more flexibility then do your research. Try the second hand market to get a better lens for your money or ask other photographers what they use and look at their images so you can compare them.

Remember that your camera will require a specific fitting. Each brand will have it’s own fitting so make sure any lenses you try or buy are made for your fitting otherwise you may damage both the lens and the camera.

I hope that helps a bit Shani, but no doubt this will generate more questions which I will do my best to answer.