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Using a focal reducer widens the angle of your lens and increases its speed
W hile most filmmakers understand what a about a focal reducer. Essentially, it’s the opposite of a teleconverter. With a teleconverter, you’re zooming in on the projected image circle of your lens. This leads to a loss of light and image quality, but zoom in because of the reduced field of view. A focal reducer works the other way, zooming out of the projected image circle. But you gain light and improve your lens’s potential image quality. Focal reducers are often referred to as ‘Speedboosters’, which is actually a term owned by Metabones. Speedbooster has become commonly used to describe all focal reducers, even from other brands, such as Kipon, Viltrox, Commlite, Aputure, Canon and Z CAM. teleconverter does, there is a lot of uncertainty How it works It’s best to start by going over some key terms that are worth knowing. Focal length is one factor that makes up your field of view. A shorter focal length offers a wider field of view, while a longer focal length narrows the field of view. A lens’s focal length is always the same, whatever the camera. The second factor determining your field of view is sensor size. If you put a 50mm lens on a full-frame sensor,
followed by a Super 35 camera, the focal length doesn’t alter; it’s the amount of the image circle recorded by the sensor that changes. So, if you used a full-frame 50mm lens and a 50mm lens designed for a Super 35 sensor, the images would be practically identical, with the same perspective and depth-of-field on the same full-frame camera. The difference is that the Super 35 lens would have heavy vignetting, because it doesn’t have the image circle size to cover the larger sensor. To work out howmuch focal length is reduced, you need to know the magnification of your focal reducer. Canon’s new focal reducer for RF mount is 0.71x, but these numbers can go as low as Metabones’s XL boosters, which are 0.64x. Subsequently, you can work out the reduction by taking the original focal length of the lens and multiplying it by the magnification factor. Taking a 50mm lens and putting it on a 0.71x focal reducer, for example, the new focal length would roughly equal 35mm. The maximum aperture also changes. This can be worked out with a calculation that divides the lens’s focal length by the diameter of the entrance pupil. It’s understandable if you don’t want to get involved with the maths. But by using a 0.71x reducer on a 50mm f/1.4 lens, it acts like a 35mm f/1.0 lens. So, even
“The termSpeedbooster has become commonly used for focal reducers”
IMAGES Focal reducers are suitable for lots of different cameras, fitting between the lens and the camera body to provide a wider field of view
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