When two or more lenses are used in an optical system, the formula used to calculate the magnification of the final image produced by the system is:
M_{system} = (M_{lens #1})(M_{lens #2})(M_{lens #3}) ....
When an optical system uses two lens, work each lens separately. Remember that the image of lens #1 will serve as the object for lens #2. If the image of lens #1 falls "in front of" lens #2, you can calculate the object distance for lens #2 by subtracting the value of d_{i} for lens #1 from the total distance separating the two lenses.
In this example, two converging lens produce a final image which is real and upright. A scaled diagram would be necessary to determine how the height of the final image, I_{2}, compares to the height of the original object, O.
A similar process will produce the image for a double lens system involving a converging and a diverging lens.
In this second example, a converging lens followed by a diverging lens produce a final image which is virtual and inverted. A scaled diagram would be necessary to determine how the height of the final image, I_{2}, compares to the height of the original object, O.
