Choose the correct option regarding lenses in contact.
A. the equivalent focal length is \(\frac{1}{f}=\frac{1}{f_{1}}+\frac{1}{f_{2}} a a a \frac{1}{f_{2}}\)
B. when two lenses are placed at a separation d, if object is at ∞, the two lenses can be replaced by a single lens of focal length \(\frac{1}{f}=\frac{1}{f_{1}}+\frac{1}{f_{2}}-\frac{d}{f_{1} f_{2}}\)
C. The equivalent lens is to be placed at a distance \(\frac{d f}{f_{1}}\) behind second lens.
D. all options are correct.
Answer:D
Choose the correct option regarding lenses in contact.
A. the equivalent focal length is \(\frac{1}{f}=\frac{1}{f_{1}}+\frac{1}{f_{2}} a a a \frac{1}{f_{2}}\) B. when two lenses are placed at a separation d, if object is at ∞, the two lenses can be replaced by a single lens of focal length \(\frac{1}{f}=\frac{1}{f_{1}}+\frac{1}{f_{2}}-\frac{d}{f_{1} f_{2}}\) C. The equivalent lens is to be placed at a distance \(\frac{d f}{f_{1}}\) behind second lens. D. all options are correct.