If you've got the money to burn and want a new lens, what are the things to look out for when hunting for the right one? Obviously, you should aim for a budget that suits you but a good lens is an investment that can outlive your camera by several generations. There's also a lot of debate on the internet about which is more important for getting a great photo, a good camera or a good lens. (Of course, the correct answer is a good photographer!) But if you need a lens, here are some things to consider: 

Primary use 

Lenses come in a vast range of focal lengths from ultra wide to super telephoto. The focal length you need depends a lot on what you will take photos of. If you work that out, then you narrow down your choices a lot. If you don't have one then a lens in the 'normal' range for your camera is a good safe start as it is close to what the human eye sees. Normal is generally considered to be equivalent to the diagonal length of you're sensor which is about a 50mm lens on a full frame DSLR camera. A longer focal length of 80-135 is a standard for portraits as this range is supposed to be more flattering. Anything over that is telephoto while anything below 35 gets wider and wider until you hit fisheye territory. You can also consider if you want a macro lens which can be focused at very close distances and get you photos of spiders knee caps etc. Some lenses can have multiple uses e.g. macro lenses can be used for portraits. Other lenses like fisheyes have less flexibility so try to establish what you need before you go shopping.

Zoom or prime

Zoom lenses have greater flexibility and are great for traveling light. Prime lenses have fewer moving parts and less to go wrong while traditionally having better image quality and sharpness. Cheaper zooms suffer from distortion and diffraction which can differ when zoomed in our out. Zooms tend to be bigger, heavier and longer while primes are lighter and general have a much lower f stop which means they are better at gathering light.

Stabiliser/vibration reduction

If you drink lots of coffee, take photos in low light or use a large telephoto lens, you will benefit from stabilisation. However, technology costs money and some lenses are double the price of their stabilisation-free versions. If you can't afford it, you can always get a monopd or tripod to keep any camera movement from affecting your photos.

Future compatibility

If you have a crop sensor camera and think you may take the big leap up to a full frame camera in future, be aware that some lenses might not fit. Canon EF-S, Nikon DX, Tamron Di, and Sigma DC lenses are only compatible with crop sensor cameras so it's best to avoid them if you want to go full frame in future. That is, unless you are rich and can afford whichever lenses you like!

Resale value

Standard kit lenses are never going to go up in value over time. Some pro lenses do cost a lot of money, but their price can even go up on the second hand market making them an investment. Certain famous lenses that are particularly reliable or incredibly unusual can go for as much or even more than originally bought for e.g. the Canon EF 200mm f1.8 lens, or the Canon 50mm f0.95 dream lens are just two which are in small numbers and big demand. With the increase in mirrorless cameras with a range of adapters, even old film lenses are making a come back. 

Aperture (constant/variable) worth zoom lenses

Cheaper zoom lenses often have a variable aperture. You can tell which ones because they will have a number like f3.5-5.6 on the front of the lens. What this means is that as you zoom the size made by the aperture blades gets smaller (the f number increases as you zoom in-try it if you don't believe me). You may not notice if you use automatic settings but this has a massive effect on your photos because the difference between 3.5 and 5.6 is 2 stops, or 4 times less light. These kinds of lenses are difficult to use in manual mode as you always have to check your settings and can't zoom once you set them (unless you use an f stop that is outside of the 3.5-5.6 range in which case it doesn't vary when zoomed. The alternative is a constant aperture lens like the Canon EF 70-200 f2.8 IS USM ii which has an aperture that stays fixed no matter if you zoom in or out which let's you concentrate more on the photo than your settings all the time.

To be continued...