![]() ![]() The photography forums are full of confused newcomers still asking about focal length, field of view, aperture etc. The bottom line is that if you only photography using a camera with an APS-C sensor, then how a 50mm lens behaves on that camera should be all that matters.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. For example a Sigma 14mm f/1.8 would need an APS-C equivalent of 9mm f/1.2, or a MFT equivalent of 7mm f/0.9. There are full-frame lenses that just don’t have a cropped equivalent. Sometimes, focal-length equivalence isn’t even possible. None of this is really that important, except to understand how a lens behaves will be different depending on the size of the sensor in the camera it is used on. Therefore a 35mm APS-C lens at f/5.6 and 800 ISO would be equivalent to a 50mm full frame lens at f/ ISO. The second is ISO equivalence, with a slightly more complication equation: Equivalent-ISO = ISO × crop-factor² A 25mm lens on a MFT sensor with a crop-factor of 2.0 gives the equivalent angle of view as a 50mm lens on a full-frame sensor.įig.4: Aperture equivalence between a 25mm MFT lens, and a 50mm full-frame lens. To achieve the same angle of view on differently sized sensors, a different focal length is needed. Figure 2 illustrates two different systems with different sensor sizes, with two lenses that have an identical angle of view. The crop-factor in any case is more of a differential-factor which can be used to compare lenses on different sized sensors. It can be derived using the following equation: Equivalent-FL = focal-length × crop-factor This is most commonly used to relate how a lens attached to a crop-sensor camera behaves in terms of a full-frame sensor. Firstly there is the most commonly used situation – focal-length equivalence. But what does equivalence mean? Well it has a number of contexts. two cameras with differing sensor sizes.īut these are the only real contexts where it is important – regardless of the sensor size, if you are not interested in comparing the sensor to that of a full-frame camera, equivalencies don’t matter. ![]() Another reason equivalency might be important is perhaps you want to take similar looking photographs with two different cameras, i.e. So an APS-C 35mm lens has a full-frame equivalency of 52.5mm which can be rounded to 50mm, the closest full-frame equivalent lens. If you want to compare this to a full-frame lens, you can multiply this by the crop-factor for APS-C sensors, so 35×1.5≈52.5mm. For example a 35mm lens has an angle of view of rough 37° (horizontal). Fig.1: Relative sensor sizes and associated crop-factors.Įasy right? But this only really only matters if you want to know what the full-frame equivalent of a crop-sensor lens is. ![]()
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