TPR Optics: Using Multiple Optical Instruments

[justadream]

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Can someone show a diagram or describe what TPR means in the following (especially with bold)?



“Optical instruments, such as mirrors and lenses, are often used to converge or diverge light. When more than one optical instrument bends light in succession, it is sometimes useful to consider the image produced by the first mirror or lens to be the object from which the light comes to the second mirror or lens [I understand up to this point!]. In such cases, the virtual object for the second instrument is sometimes on the opposite side of the instrument as the incoming light. The convention for these objects is that their distances are negative in optics equations.”

 

[Cawolf]

If the image produced by the first lens falls closer to the viewer then the second lens (behind it) - then when doing calculations this object has a negative distance.

I am kind of poor at drawing ray diagrams or I would show you. Just picture a second lens that it closer to the first lens than the image of the first lens.

 

[justadream]

@Cawolf
Would the order be like this?

Incoming Light______First Lens _______Second Lens _____Image of First Lens

 

[Cawolf]

Yes exactly.

And when the object is behind the lens the distance is negative, just like an image on the same side as the light is negative.