The following figure illustrate the optical design of a fundus camera. The objective lens L1, in combination with the eye lens, forms a real image of the retina in the intermediate plane P1. The corresponding magnification is 2. The focal lengths for lens L2 and L3 are 40 mm and 10 mm, respectively. A CCD camera is used to capture images formed in plane P2.  a. The focal length of L1 should be [Fill in the blank], mm. b. The magnification of the lens system L2/L3 is [Fill in the blank], . c. The magnification of the funds camera is [Fill in the blank], . Round your answer to two significant figures.  多项填空题