A microscope objective with a magnification of 15 is used in a microscope with a magnification of 51. Find the focal length of the ocular if the ocular's image is formed at the eye's near point, 23 cm from the eye. Neglect the distance between the eye and the ocular.

A microscope has an objective lens with a focal length of 16.22 mm and an eyepiece with a focal length of 9.06 mm. With the length of the barrel set at 33.0 cm, the diameter of a red blood cell's image subtends an angle of 1.43 mrad with the eye. If the final image distance is 33.0 cm from the eyepiece, what is the actual diameter of the red blood cell? Hint: To solve this equation, go back to basics and use the thin-lens equation. ?m

A student with normal sight is surprised to see a possum scampering up the rear wall in the Lyle theatre. The possum is 30.0 cm long and the wall is 2.3 m away. The student's eyeballs have a diameter of 2.4 cm. How big is the image of the possum on the student's retina? (Units: cm)

The projection lens in a certain slide projector is a single thin lens. A slide 24.8 mm high is to be projected so that its image fills a screen 1.82 m high. The slide-to-screen distance is 3.04 m. (Enter your answers to at least one decimal place.) (a) Determine the focal length of the projection lens. mm (b) How far from the slide should the lens of the projector be placed to form the image on the screen? mm