How do you Measure focal point of diverging lens using converging lens?

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A convex lens focal point can be measure but shining parallel light through it and seeing where the rays meet.

To measure a diverging lens, a converging lens is required of known focal length because a real image is needed.


I am finding it impossible to imagine such a double lens system where u can measure the div f.
Could anyone explain this, or draw this?

Originally Posted by johnwandering

A convex lens focal point can be measure but shining parallel light through it and seeing where the rays meet.

To measure a diverging lens, a converging lens is required of known focal length because a real image is needed.


I am finding it impossible to imagine such a double lens system where u can measure the div f.
Could anyone explain this, or draw this?

Think about concave diverging contact lenses that help near sighted individuals correct for an image forming before the retina.... by using the concave contact pushes the concave converging lens of the eye's focal point back

http://www.youtube.com/watch?v=PHFm0R4d0Vg