1. A colour measuring system for measuring colour in a printed image printed by a printing press, comprising: a camera system configured for recording a respective image of the printed image using a first and second optical sensor, the camera system comprising: a pair of optical sensors, the pair comprising the first and second optical sensor, each configured to record the respective image of the printed image, wherein an angle of view of the first optical sensor overlaps an angle of view of the second optical sensor in an overlap area and the printed image is situated at least partially in said overlap area, and each of said first and second optical sensors has an entrance pupil placed at a predetermined distance from each other; and a processor operatively coupled to said first and second optical sensors, wherein the processor is configured to determine a focal distance from at least one of the first and second optical sensors to the printed image using the predetermined distance, the angle of view of at least one of the first and second optical sensors, and an overlap of the respective images, wherein said focal distance is measured from the entrance pupil of at least one of the first and second optical sensors to the printed image; and a colour corrector configured to: perform a colour calibration of the first and/or second optical sensor at the determined focal distance; and correct a light intensity detected by the calibrated first and/or second optical sensor.