An introduction to Lenses



What is focal length?
Focal length is measured in millimetres. See more about how focal length works in my other post (coming soon). To know the essentials just remember that the bigger the mm of the lens, the farther your lens can zoom. The smaller the mm of your lens, the wider your shot will be.
A lens with a large focal length is known as a ‘telephoto’ lens, e.g. 180mm. Whereas a lens with a small focal length is known as a ‘wide angle’ lens, e.g. 28mm. 
Most lenses have a variable focal range, this is useful when you're shooting a variety of subjects as it allows you to alter how your photograph is framed more easily.


What is a prime lens?
A prime lens is a name given to a lens that is a fixed focal length. A fixed focal length means that you cannot zoom in or out with your lens. Prime lenses tend to produce much sharper images than other lenses, this is mainly due to the fact that there are no moving elements of glass within the lens, as it does not need to do any zooming. 


How do I choose which focal length to use?
Depending on what you’re photographing, you will need a lens that suits the purpose. 

If you are going to be photographing things that are very far away, but want your subject to fill your frame, you would need a lens with a longer focal range, e.g. a telephoto lens. 
For example, telephoto lenses are very popular for bird watching, or sports photography. On both of these occasions you are likely to be taking photos far away from your subject.

For landscape or street photography, a wide angle lens is very useful. A wide angle lens will allow you to fit a lot more of the scene in front of you into your photograph.

‘Nifty Fifty!’ This is a nickname for a 50mm lens (it’s fixed at 50mm, so it’s a prime lens). This focal length is renowned for it’s versatility. It’s great to use in a wide range of situations, especially portraits. A 50mm lens portrays a perspective that is the closest to what the human eye sees.


Perspective
As well as allowing you to frame your scene differently, the type of focal length you choose will alter the perspective of the subject in your photograph. 

For example, a very wide angle lens can create a stretched look to your images, this is mainly noticeable on the edges of the frame. An extreme example of this can be seen when looking at an image taken with a ‘fisheye’ lens. In this case the angle of the lens is so wide it alters the perspective of the image to the point where the subject is very distorted. See example below.



A telephoto lens can have the opposite effect. Objects in photographs taken with a telephoto lens can appear closer together than they actually are. 


Aperture
Lenses vary in their aperture range. Depending on what you're photographing, you might want to check what the minimum aperture is when choosing which lens to shoot with. For more about aperture see this article





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