All points in the main array are cross-type (sensitive to both horizontal and vertical detail), and usable with a minimum aperture of f/5.6. The Canon 7D's AF system has a total of 19 points, arranged in a diamond-shaped pattern. The AF system is now also more integrated with the exposure metering system, but we'll discuss that separately, in the Exposure section. The Canon 7D incorporates an all-new AF system, with a new AF array, enhanced focus mode options, new servo tracking algorithms, and automatic correction to increase focus accuracy under artificial lighting. Lens Peripheral Illumination Correction first appeared in the Canon 5D Mark II, and was also included in the midrange Canon 50D. The Canon 7D also offers Lens Peripheral Illumination Correction, which corrects for lens shading (commonly called "vignetting"), producing uniform exposure across the frame by compensating for the light falloff seen with some lenses in the corners of the frame. For example, a 100mm lens on the Canon 7D will show the same field of view as a 160mm lens on a camera with a 35mm frame size. While most properly called a "crop factor," the 1.6x ratio is most commonly referred to as the "focal length multiplier," since that's how it works in practice: Any lens used on the Canon 7D will have the same field of view as one with a 1.6x greater focal length will when attached to a 35mm camera. The sub-frame sensor on the Canon 7D means that it has a smaller angle of view (by a factor of 1/1.6x) than a full-frame camera with any given lens. EF-S lenses can't be used on Canon's full-frame cameras, nor on their models with 1.3x crop factors, like the current EOS 1D Mark III, but small-sensor cameras like the 7D can use any full-frame lenses in Canon's arsenal. Designed with a smaller image circle (the area covered by the image on the film/sensor plane), EF-S lenses tend to be smaller and lighter than full-frame models with the same focal length and maximum aperture. The Canon EOS 7D will work with pretty much any EF-mount lens ever made, as well as with the special EF-S lenses designed for cameras with APS-C size sensors.