Focal length multiplied by wavelength

AI Thread Summary
The discussion centers on the physical significance of multiplying the focal length of a lens by the wavelength of laser light. This product relates to image size on the image plane, with a reference to the Rayleigh Criterion, which defines the resolution limits of a lens. The correct expression involves the f-number, which is the focal length divided by the lens diameter, rather than just the focal length. The use of a Spatial Light Modulator (SLM) to create the object at the focal plane is noted as a relevant factor. Understanding these concepts is crucial for accurate image resolution and optics.
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Simple question: is there any physical significance of the quantity (focal length of lens)*(wavelength of laser light passing through the lens) ? How does it relate to the size of an image on the image plane? According to my professor, (focal length)*(wavelength)/(constant) is the length of the image.

Also, we are using an SLM to create the object (at the focal plane), if that makes any difference..
 
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I suspect that your prof is talking about the Rayleigh Criterion, which describes the resolution of a lens - the minimum angular separation of two point sources such that they will be recognisable as two sources in the image. The expression you are quoting isn't quite right for that - it's the f-number (the focal length of the lens divided by its diameter), not the focal length itself that you use.

Wikipedia on the subject. Born and Wolf is the bible for this kind of thing, if your library has a copy.
 

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