When framing a photograph, it’s not just the focal length that matters. In this tutorial we’ll show you how to choose the optimum angle of view for your scene, as well as explain how to choose the right lenses and the difference between angle of view vs field of view. First up, we answer some of the most common questions about the angle of view in photography…
What is angle of view?
Angle of view is the maximum view a camera is capable of ‘seeing’ through a lens, expressed in degrees. The choice of focal length is obviously key here, with longer lenses having a narrower angle of view than shorter lenses.
For instance, a 200mm lens has an angle of view of 12 degrees, while a 20mm lens offers a wider angle of view of 94 degrees on a full-frame camera.
When it comes to zoom lenses, the angle of view changes according to the focal length the lens is zoomed at.
However, the size of the imaging sensor inside the camera also affects the angle of view.
Why does sensor size matter?
The majority of lenses are designed for full-frame digital SLRs. These are cameras where the sensor is approximately the size of a frame of standard 35mm film.
So, with a full-frame camera, what you see is what you get (well, it is if you use Live View – more on that later).
However, most digital SLRs have a sensor that’s smaller than a full-frame one, and similar in proportion to the old-school APS-C film format.
Sensors this size see a smaller part of the image through the lens, and consequently everything looks bigger in the frame.
So smaller sensors increase the focal length of a lens?
No, the focal length isn’t increased at all – a 50mm lens is a 50mm lens, regardless of the camera it’s attached to.
It’s just the angle of view that gets narrower, so it appears as if you’re using a longer lens.
To work out what this ‘equivalent focal length’ is – the one that would give a similar angle of view on a full-frame camera – you need to multiply the actual focal length by the ‘crop factor’ of the sensor.
This crop factor varies a little between manufacturers: with Canon APS-C cameras, this is a factor of x1.6, and with Nikon DX format cameras, it’s x1.5.
For example, a 35mm lens attached to a Canon 70D gives an equivalent focal length of 56mm (35 x 1.6).
Why do I need to work out the equivalent focal length?
It provides a standardised way of comparing lenses across different types of camera. In fact, the only time you really need to take the equivalent focal length into account is when you’re choosing a lens.
For wildlife and sports photography, where getting close to the subject is often impractical, cameras with smaller sensors can be a real benefit.
A 400mm lens fitted to a Nikon D7100 gives you the equivalent field of view of a 600mm lens on a full-frame DSLR.
Attach a x1.4 teleconverter to the lens, and the effective focal length becomes a whopping 846mm ((400 x 1.4) x 1.5)! For landscape photographers using wide-angle lenses on smaller sensor cameras can be potentially problematic.
Using a 16-35mm zoom on an APS-C camera effectively gives you the same view as a 24-53mm lens on a full-frame camera.
To squeeze as much into the picture as you could with the lens attached to a full-frame camera, you’d need to move further away, which isn’t always practical.
So if I want to go wide, I need to get a really short focal length lens?
If you’re using a camera with an APS-C sensor, yes, you do. Fortunately, camera and lens manufacturers have ‘digital lens’ lines dedicated to cropped frame sensors, such as Canon’s EF-S, Nikon’s DX and Sigma’s DC ranges.
A 10-20mm digital lens on an APS-C format SLR gives approximately the same angle of view as a 16-35mm lens on a full-frame camera.
So should I buy full-frame lenses or APS-C lenses?
If you think you’ll upgrade from an APS-C camera to a full-frame one in the future, then it’s worth buying full-frame lenses so you can continue to use them.
If you try to attach a Canon EF-S lens to a Canon EOS full-frame camera, there’s a risk you’ll damage it.
However, you can use a Nikon DX lens on a Nikon FX (full-frame) SLR, but the camera will automatically switch to ‘DX crop mode’.
This means that only the central part of the sensor is used, and the resolution drops significantly.
This cropped area will be indicated in the viewfinder, so you can compose shots accurately.
You mentioned Live View earlier – why is this better?
When a camera is used in Live View mode, the rear screen shows the full field of view recorded by the camera sensor. Some camera viewfinders also show the entire image, but the majority don’t.
Because you can’t see the entire frame, you may have to crop the image slightly later.
Why can’t I just use one lens and crop the image to get the size I want?
You can, but cropping the image after you’ve taken the shot means that you aren’t using the full potential of the camera sensor because fewer pixels are used in the cropped area.
Angle of view and sensor size
