Optics - Defining front and back of lens

[MichaelT]

Working on some optics problems and I am confused about the front and back of the lens. The sign conventions are key to finding the correct image location. Now, is the front always where the object is located?

The problem I am working on involves a divergent lens and a concave mirror. The object is in front of the lens. An image forms in front of the lens. Then the concave mirror forms an image between the lens and the mirror, which would be on the opposite side of the lens.

Would the object now be considered as being in back of the lens, or would it be the front? The other side of the lens was previously the front. Does this change, or is one side considered the front for the whole problem?

Thanks!

 

[rl.bhat]

Instead of saying front and back of lens, you can say , the face which receives the ray and the face which refract the ray. Measure the distances from the center of the lens.

 

[tomcue]

In optics, the front and back of a lens are defined based on the direction of light propagation. The front of the lens is where the incoming light rays enter the lens, while the back is where the light rays exit the lens. In general, the object that is being viewed or observed is located in front of the lens, so the front of the lens is typically associated with the object. However, in some cases, such as the problem you are working on, the object may be located on the opposite side of the lens. In this case, the front of the lens would still be considered where the incoming light rays enter, and the back would be where the light rays exit. So in your scenario, the object would be considered in the back of the lens, as it is on the opposite side of the incoming light rays. The front and back of the lens do not change throughout the problem, but rather remain constant based on the direction of light propagation. I hope this helps clarify the concept for you.