The angle of view decreases to the extent that it's now the same as that of a 44.8mm lens mounted on a full frame camera. In fact if you put that same 28mm lens on a Canon EOS crop sensor camera, the angle of view decreases as you can see from the figure above. That's why a 28mm lens on a full frame 36x24mm gives a wide view ( red lines), but on a smaller format camera such as one using and APS-C crop sensor, it's not so wide ( blue lines). The diagram below shows why.Īs you can easily see from the diagram, the larger the format, the wider the angle of view for a lens of a given focal length (shown by the red lines for the larger format and the blue lines for the smaller format). The field of view (which is what "wide" is all about) is actually determined just as much by format size as by focal length. In fact this is true ONLY if that lens is making a 36mm x 24mm image. We've been trained to think that a 50mm lens is "normal", a 35mm lens is "wide normal", a 28mm lens is "wide", a 24mm lens is "very wide", a 20mm lens is "super wide", a 16mm lens is "ultrawide" and so on. The problem is that most of us have been trained to think in terms of focal length rather than field of view when comparing lenses. All 35mm lenses and lenses designed for use on APS-C DSLRs are marked with their true, actual, focal length. Whether you mount that lens on a 35mm camera, a medium format camera of a large format camera doesn't change its focal length. 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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