Featuring an impressively high-resolution 32.5MP APS-C CMOS sensor, the 90D is capable of producing imagery with notable clarity and dynamic range, as well as a broad sensitivity range of ISO 100-25600 and low noise to support working in difficult lighting situations. The sensor and image processor also realize fast performance throughout the camera system, including the ability to shoot continuously at up to 10 fps, record UHD 4K30p video, or record high-speed Full HD 1080p video at 120 fps.

Benefitting stills shooting with the optical viewfinder, a wide-area 45-point all cross-type phase-detection autofocus system provides quick and precise focusing in difficult lighting conditions down to -3 EV. For working with telephoto lenses fitted with extenders, 27 of the points are capable of focusing down to f/8 and the center dual cross-type offers increased precision at brighter aperture values. The cross-type design of the sensors affords greater accuracy in low-contrast and mixed lighting conditions, and the broad coverage of the 45 sensors is ideal for tracking and maintaining focus on moving subjects. Making use of the 45-points is a series of four AF area selection modes, including single-point AF; Zone AF, where you can select from one of nine AF zones; Large Zone AF, which offers a choice of three selectable zones; and 45-point AF auto selection, which allows the camera to select a single point automatically.

When recording video or shooting in live view, a Dual Pixel CMOS AF system is employed that features 5481 selectable autofocus points. This focusing system offers smooth and fast focusing performance in a similar manner to how a camcorder acquires focus. Dual Pixel CMOS AF integrates two separate photodiodes within each pixel to provide a broad and dense network of phase-detection gathering elements across a majority of the image sensor to reduce focus hunting for faster, more direct control of focus placement. When working with still imagery, this focusing system works to acquire focus quickly and accurately, making it ideally suited to shooting and tracking moving subjects so that critical focus is attained with each shot. When shooting video, a Movie Servo AF mode offers smooth and natural focusing when changing from different subjects or different distances within the scene, as well as the ability to specify tracking sensitivity, AF speed, and Face Tracking priority. Benefited by the Touch AF system, rack focus is possible simply by touching elements within the scene on the touchscreen in order to change focus in an intuitive manner. Subject tracking in movies is also heightened due to the Dual Pixel CMOS AF system's ability to recognize subjects and maintain focus when working within changing or cluttered scenery.