However, it soon became apparent that not all EF-S lenses needed the shorter back focus. This distance is shorter for some EF-S lenses than for EF lenses. Back focus is simply the distance between the rear of the lens and the digital sensor. The press release for the EOS 300D talked about the ‘short back focus’ of EF-S lenses. It is either ‘Short’, as in short back focus or ‘Small’, as in small image circle. EF and EF-S lenses fit the EF-S mount, but only EF lenses fit the EF mount. EF-S lenses create a smaller image circle to suit the APS-C format. In 2003 Canon introduced the first EF-S lens, alongside the EOS 300D. EF lenses have an image circle large enough to cover the full- frame format of film and some digital models. A range of EF lenses was introduced at the same time and the number has increased over the years. When Canon introduced the EOS camera system back in 1987 it featured a new lens mount – the EF mount (short for ‘electro-focus’). This is much more useful than knowing the crop factor. These are the benchmarks for identifying lens types.Ī focal length greater than the standard is telephoto and a focal length less than the standard is wide-angle. On an APS-C camera it is around 27mm (43mm divided by 1.6). On a full-frame camera this is 43mm – and so typically a 50mm is regarded as a standard lens for full-frame purposes. Our advice? Forget about crop factors! And extended reach, too!Ī standard focal length for a camera is usually taken as the diagonal of the image frame. But that is not a common situation for most of us, so it is best just to get used to the view given by a lens on your camera. So essentially this means that if you have a full-frame and an APS-C camera side by side, you need a longer focal length lens on the full-frame camera to see the same view as the APS-C camera. Similarly, the full frame sensor is 1.3x larger than the APS-H sensor.) The maths… We multiply because the full-frame sensor is 1.6 times bigger than the APS-C sized sensor. The rest of the image falls outside the area of the APS-C sensor.įACT: All lenses produce circular images, but the sensor (or film negative) only collects the data that falls onto its rectangular surface area.Ī crop factor of 1.6x – often talked about with APS-C cameras – can be explained like this: If you are using a 50mm lens on an APS-C camera and you want to shoot the same scene with the same field-of-view with a full-frame camera you need a focal length of 50 x 1.6, which is 80mm. There is no change to the image created by the lens – it’s simply that the smaller sensor only captures the central area of the image. You could get an identical result by enlarging and cropping the full-frame image. It is a magnification effect, not a change of focal length. In fact, the APS-C image has been enlarged more than the full-frame image to match the display size. The result from the APS-C sensor is shown above and appears to show an increased telephoto effect. When you come to display an image to fill a computer screen or a print, the result from the full-frame sensor is shown above. The field-of-view is narrower, but nothing else changes. The end result is a smaller area captured, but exactly the same as the central area of the full frame image. An APS-C camera only records a part of the full image (as shown by the white box on the central image). A full-frame camera captures the full image. The original shot was taken with an EF 400mm lens. The focal length might not change, but what does change is the field-of-view. Use the same lens on a full frame camera and an APS-C camera, and you end up with results like those below. It doesn’t.įACT: Focal length is a characteristic of the lens and is not affected by the camera or sensor size. There is a lot of confusion about crop factors, extended reach and telephoto effects when using lenses on APS-C cameras.įirst, let’s dispel the myth that the focal length of a lens changes when switched between a full-frame camera and an APS-C camera. So what does this all mean for your photography? Crop refers to the fact that the image you get with the smaller sensor is a cropped part of the image obtained with the full frame sensor. The main reason for the introduction of the smaller sensor was cost – full frame sensors are expensive. Then, in 2000, along came a camera with an APS-C 'crop' sensor – the EOS D30. EF lenses, like the FD lens system that went before, gave full coverage to 35mm EOS film cameras, then subsequently full-frame – 36 x 24mm sensor – digital cameras. The EF lens mount was introduced in the same year that the EOS was announced – 1987. Terms like ‘crop factor’, 'extra reach’ and ‘equivalent focal length’ just aren’t helpful. This is exactly what happened – as far as we’re concerned – when Canon introduced the EF-S lens mount. Sometimes when an attempt is made to simplify or explain a term or reference point, it can end up complicating the situation.
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