Friday, 4 July 2008

Photographic Terminology Part 1

It's an interesting time for participating in web forums on photography, equipment and taking photos. Newbies and seasoned photographers often scratch their head when they read abbreviations or terms in forum posts. I'll try to keep a record of the various abbreviations.

Abbreviation Elucidation
AOV In photography, angle of view describes the angular extent of a given scene that is imaged by a camera. It parallels, and may be used interchangeably with, the more general visual term field of view. (Wikipedia)

Bernd Harlos's interactive demonstration (specific to the Four Thirds sensor size), Tamron's interactive Focal Length Comparison and the Contra-zoom aka dolly zoom animation from Wikipedia
FOV The field of view (also field of vision) is the angular extent of the observable world that is seen at any given moment. (Wikipedia)
Digital Sensor Crop Factor vs FF (35mm Full Frame) In 1913, Oskar Barnack developed the prototype Leica camera around the 24x36mm film size. This became the standard film size 35mm film SLRs. When the Digital DSLR was invented, it was a different medium and it was expensive to make such a large sensor. So different brands used as a basis, a smaller sensors.

When you take any lens and fit it on a camera successfully, that camera's true optical focal length(s). Let us take for example, 50mm on a 35mm film camera. Now, for the Four Thirds consortium, their reference sensor is not 24x36mm, it is 13.5x18mm. Even if the lens displays a large area, the sensor only sees a smaller rectangle of it, the rest of the image is "wasted". Put it simply, it's like taking masking paper and cropping away the "unseen" area. This crop factor for Four Thirds is 2x.

Take 2 people. Stand away from them with a film camera and the 50mm lens. You take a photo of 2 people. Take that same lens, same scene, but mount the lens on a Four Thirds camera. You will see 1 person in the photo. It feels to you that you are magnifying the scene by 2x. If you walk backwards a bit, you can fit both people into the photo, but you will have now changed your distance and your perspective.

Since longer lenses magnify things, it appears that this real 50mm lens when mounted on a Four Thirds camera works like a 100mm lens in terms of AOV.

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