The focal length of a lens is the focal length of the lens. So why does the format size matter and what effect does it have on focal length? Well the answer to the second part of the question is "none". The "crop" name comes from the fact that if you take a full frame image (24x36mm) and crop the center 15x22.5mm out of it, you get an image the size of "crop" sensor cameras. This just happens to be close to the image size which was used with the short-lived APS film format, specifically the APS-C image size of 25.1 × 16.7 mm (there was also APS-H and APS-Panoramic format). So camera makers decided to use a smaller sensor, around 15mm x 22.5mm. In the early days of digital sensors it was not possible to make digital sensors that big in any sort of quantity, and the ones you could make were so expensive that hardly anyone would have been able to buy a camera which used one. A full frame 35mm camera (whether it uses film or a digital sensor) records an image that is approximately 36mm x 24mm in size. No wonder people get confused.įirst, what is a crop sensor camera? Well, it's simple. the focal length that corresponds to the "6.1-35mm" written on the digicam lens. However.when it comes to DSLRs they don't tell you the "equivalent" focal length, the tell you the true focal length, i.e. However if you actually look at the camera you will see " 6.1-30.5mm 1:1.8-2.8" written on it, so Canon is applying a multiplier to the description of their lens and telling you what equivalent lens on a 35mm full frame camera would give you the same field of view as the lens on their small sensor digicam. For example the Canon website describes the Powershot G15 this way "The excitement starts with the newly developed 5x Optical Zoom with 28mm Wide-Angle, bright f/1.8 (W) – f/2.8 (T) lens". The confusion isn't helped buy that fact that compact digicam lenses are often described by their manufacturers in terms of "equivalent" focal length, while their APS-C lenses are described in terms as actual focal length. The photography forums are full of confused newcomers still asking about focal length, field of view, aperture etc. Crop Sensor (APS-C) Cameras and Lens Confusionĭespite the fact that so called "crop sensor" digital SLRs have been with us since 1999 (the Nikon D1, with the Canon 30D following in 2000), there's still a huge amount of confusion out there about exactly what a "crop sensor" camera is and what effect is of using a lens with a crop sensor camera rather than a full frame camera.
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