Does the Thickness Affect a Semi-Mirror Spherical Lens' Characteristics?

[Ozen]

Hello,

I am trying to get a better understanding of optical lens's and came across a question I have not found an answer to. Say you have a lens made of either Polycarbonate or Trivex, and it is a spherical lens. A coating is applied to the side with the smaller radius to reflect certain light wavelengths. Would there be any effect thickness would play on whether this would work or not? Light is meant to pass right through the lens without distorting, diverging, converging, etc; like how traditional lens do. The sole purpose for the lens is just to reflect that specified wavelength back. For that reason I am led to think that the thickness would not matter. I just wanted to confirm with those who are way more informed in this field than I am if thickness indeed is not relevant.

Thanks for any help!

 

[Cutter Ketch]

Light is meant to pass right through the lens without distorting, diverging, converging, etc; like how traditional lens do.

I’m confused. Since when does light pass right through a traditional lens without distorting, converging, or diverging the light? That is literally the definition of a lens. If it doesn’t diverge or converge the light we call it a window. Are you talking about a flat plate like a window?

 

[Ozen]

I’m confused. Since when does light pass right through a traditional lens without distorting, converging, or diverging the light? That is literally the definition of a lens. If it doesn’t diverge or converge the light we call it a window. Are you talking about a flat plate like a window?

Thank you for the reply. I'm not sure what the correct term for the lens/window I am describing is. The optic in question is shaped like "(". My question involves the thickness of it. In the application that spawned this question, to my knowledge, the light remains unaffected by the optic. The particular application is a reflex sight for rifles. My college classes mostly focused on "()" and "l(" style optics, which I know redirect light. We only discussed spherical lenses as mirrors. But what I'm curious about is it being only partially a mirror. Hopefully this clarifies my question a bit.

 

[Cutter Ketch]

That shape is usually called a meniscus lens. If the two surfaces are concentric, then the shape doesn’t diverge or converge light. In most cases that isn’t called a lens but a dome.

Now, I say a dome doesn’t converge the light, but that isn’t quite right. A dome does perturb the light particularly while the light is inside the material, and the thickness definitely matters.

Your question about the mirror surface doesn’t have a simple answer. If the coating is a dielectric stack, then the most important thing is the angle at which rays reach the coated surface. A ray entering the larger radius surface at some angle will refract, but not all the way to perpendicular. If you continue tracing the ray inside the material you’ll see that the angle that the ray hits the inner surface depends on the thickness of the dome. It is certainly possible to construct a situation where the mirror coating gives different behaviors for different dome thicknesses. On the other hand, if the incident angles aren’t too steep it is possible to construct a dome where the thickness isn’t too important over a range.

 

[Andy Resnick]

Summary:: Does the thickness of a semi-mirrored spherical lens have any effect on it? The semi-mirror reflects only a select range of wavelengths while it is still let's wavelengths pass through it.

Hello,

I am trying to get a better understanding of optical lens's and came across a question I have not found an answer to. Say you have a lens made of either Polycarbonate or Trivex, and it is a spherical lens. A coating is applied to the side with the smaller radius to reflect certain light wavelengths. Would there be any effect thickness would play on whether this would work or not? Light is meant to pass right through the lens without distorting, diverging, converging, etc; like how traditional lens do. The sole purpose for the lens is just to reflect that specified wavelength back. For that reason I am led to think that the thickness would not matter. I just wanted to confirm with those who are way more informed in this field than I am if thickness indeed is not relevant.

Thanks for any help!

It sounds like you are describing a lens with a dichroic coating applied to one (curved) surface. Dichroic coatings are typically multilayer thin films and their spectral reflectance/transmission qualities generally vary with incident angle. One a curved surface then, the spectral reflectance of your coating will vary.

More exotic devices like 'grisms' and grating lenses have been developed, but I've never used them.

https://wasatchphotonics.com/technologies/grisms-uses-advantages/
https://www.osapublishing.org/ao/fulltext.cfm?uri=ao-54-22-6666&id=322997
https://www.osapublishing.org/view_...q=0&mobile=no&org=Cleveland State University

 

[berkeman]

reflex sight for rifles

Do you mean like a reflective "red dot" sight?

https://www.burrisoptics.com/blog/sights/how-a-red-dot-sight-works

There is a good Wikipedia article about them:

https://en.wikipedia.org/wiki/Reflector_sight