# Optics questions...aspheric rings?



## gcbryan (Aug 25, 2011)

Most flashlights with an aspheric lens seem to have various rings. Is this a necessity with an aspheric or something that can be avoided with a better quality aspheric?

I'm not taking about the "Cree Ring" or the artifacts present when using as aspheric with a reflector.

Just using an aspheric alone you frequently see the bright emitter area, then the Cree Ring (which can be painted out) and then a dark area and then another ring of light, another dark area and then another ring of light.

I've done a little testing and this seems to come from the aspheric itself and not from the emitter or reflections inside the head, or from anything external to the aspheric.

Is this just because it's a simple (as opposed to complex multi-lens system) lens? What is actually causing those rings?


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## ma_sha1 (Aug 25, 2011)

It's a combination of Lens quality and Cree XRE dome.

Here is an example of a perfect aspheric spot from high quality AR coated lens + SST-50:


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## gcbryan (Aug 25, 2011)

Nice shot! 

I have some that probably wouldn't be apparent in that setting though since there is ambient room light. When I go out where it is dark some other rings are apparent. Do you have none of that with the one in the picture?


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## gcbryan (Feb 14, 2012)

Where does one get an aspheric with an anti-reflection coating?


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## Th232 (Feb 14, 2012)

CVI Melles Griot offers AR coatings on their aspherics. So does Thorlabs, and I presume most other good lens manufacturers.


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