Focal Lengths and Angle-of-View (AOV) Explained
For a lot of Pro AV integrators, selecting the right Angle-of-View (AOV) for a conference room or huddle room can be a challenge. To help, we’ve put together a quick overview on camera lens focal lengths and how they affect the AOV of the final picture, so you can make sure you have the right lens for the room.
When it comes to installing cameras for conference rooms or huddle spaces, there is no one lens size that fits all. One of the great features about Marshall’s high-definition POV Cameras is that they have interchangeable lenses to change the Angle-of-View depending on the size of the room or type of shot needed.
What is focal length?
Focal length is the distance between the front of the lens and the point behind it where the light comes into focus, which for most cameras today is positioned where the image sensor chip is located. This distance between the lens and the sensor is the lens focal length.
What is Angle-of-View (AOV)?
The AOV is a measurement (in degrees) of how much of a scene can be viewed through the lens. The AOV can be measured horizontally, vertically, or diagonally.
For most Pro AV integrators, horizontal AOV is going to play the biggest role in framing the shot, because the focus is typically on individual people as they speak from sitting positions behind desks.
How is focal length and AOV related?
The longer the focal length, the narrower the AOV, and vice versa.
Generally speaking the shorter the focal length, (therefore wider AOV), the more curvature a lens will produce in the corners of the image. This is due to aspherical design elements in glass lenses, and these design elements being amplified the closer the lens glass gets to the sensor.
*On a 1/3″ sensor, fisheye lenses are typically lower than 5mm focal lengths; between 5mm — 2mm will produce between 60°~180° horizontal AOV, which can be enhanced or corrected somewhat through optical design.
**The human eye has a focal length of about 22mm and an AOV “cone of visual attention” measuring about 55° wide.
How to Apply AOV to Conference and Huddle Rooms
To determine the right focal length lens for a conference room or huddle room, consider the distance from the camera lens to the subjects first, and then factor in the width and height of the desired image frame.
Here are two illustrations to give you an idea of how different focal lengths change the AOVs on some of our Marshall pro-series cameras:
In the above illustration, a Marshall CV502-U3 Full-HD USB Camera is affixed atop a projection monitor on the wall, shooting a room with a conference table about 12 feet away. As the focal lengths increase, the frame crops in tighter and the perspective distortion goes away.
For a small, huddle room installation, the subjects are often about three feet away from the camera. This illustration shows how the AOVs from Marshall CV500-series cameras get smaller as the focal length is increased (going from left to right).
Marshall has a variety of different interchangeable HD lenses for its pro-series POV Cameras. You can adjust the focal lengths for each to customize the AOV for any installation. Read more about our interchangeable varifocal lenses here.