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Also known as a reverse or inverted telephoto, this lens design has a diverging lens element positioned in front of the aperture and a converging element positioned at the rear. This makes the distance from the rear of the lens to the focal plane longer than the lens focal length. Retrofocus design has been adopted in wide-angle lenses so the rear of the lens does not impede the movement of an SLR camera's reflex mirror.
Flash synchronisation that was once used with focal plane flashbulbs.
Chromatic aberration, also called "colour fringing" or "purple fringing", is caused by a lens not focusing different wavelengths of light onto the precise same focal plane and/or by a lens rendering a different magnification each of different wavelengths. These two different types of chromatic aberration can both occur in one and the same image. Chromatic aberration can be seen as colour fringing around the boundaries that separate dark and bright parts of the image. It most frequently occurs around the edges of the image, especially in wide angle shots. Despite begin called "colour fringing" or "purple fringing", chromatic aberration can also affect black and white photography. Although a black and white image obviously has no colours in it, chromatic aberration can blur the image.