Chromatic Aberration in Glass Coated Mirros

[liveforsnow00]

Does chromatic aberration occur in mirrors that have glass coatings?
Even to a very small degree?

 

[kevinalm]

Not sure what you mean. First surface mirrors with an antireflexion coating. No. Even a thicker layer won't have any appreciable chromatic abberation provided the transparent layer is of uniform thickness over the entire mirror. Of course, we're talking in relative terms. An optical system's chomatic performance only has to be good enough so that the eye's intrinsic chromatic abberation swamps it out.

 

[blobrana]

Does chromatic aberration occur in mirrors that have glass coatings?
Even to a very small degree?

Hum,
as was said, if the light passes through glass, or similar, then this will cause chromatic aberration.
Chromatic aberration is caused by refraction, not reflection.
In reflecting telescopes the aberration is so small that, essentially, they can be said to be free from chromatic aberration.

 

[liveforsnow00]

In reflecting telescopes the aberration is so small that, essentially, they can be said to be free from chromatic aberration.

but you did say that there is some chromatic aberration, even if it is too little to see. light is refracted as it passes through glass, reflects off the mirror, passing through the glass again.

assuming that the glass is uniform throughout the mirror, the aberration would be small enough to be considered free from chromatic aberration. however what if the glass wasn't uniform and had astigmatisms, would the light be changed as it passed through the thicker parts of the glass? perhaps creating some chromatic aberration?

 

[2inquisitive]

liveforsnow00,
Reflecting telescopes use first surface mirrors. The mirror coatings are on the same side that reflects the light, so the light does not pass through any glass, except the eyepiece. Chromatic aberration can be introduced by lower quality eyepieces, filters, etc., but not the mirrors themselves. Projection TVs also use first surface mirrors and some of the less expensive ones do not even use glass in their mirrors. The coatings are sometimes applied to compressed fiberboard, etc.

 

[liveforsnow00]

liveforsnow00,
Reflecting telescopes use first surface mirrors. The mirror coatings are on the same side that reflects the light, so the light does not pass through any glass, except the eyepiece. Chromatic aberration can be introduced by lower quality eyepieces, filters, etc., but not the mirrors themselves. Projection TVs also use first surface mirrors and some of the less expensive ones do not even use glass in their mirrors. The coatings are sometimes applied to compressed fiberboard, etc.

did you read the title of my thread?

 

[2inquisitive]

did you read the title of my thread?

Yes. By 'mirro' I assumed you meant mirror. As to your question, what type of mirror has a glass coating?

Does chromatic aberration occur in mirrors that have glass coatings?

Define which type of mirror your question pertains to. Define what type of coatings you are referring to.

 

[blobrana]

but you did say that there is some chromatic aberration, even if it is too little to see.

Yeah,
The light as it passes through protective coatings, glass etc would be, technically, refracted.
It is a bit of a nit pick though.

 

[liveforsnow00]

Yes. By 'mirro' I assumed you meant mirror. As to your question, what type of mirror has a glass coating?

Define which type of mirror your question pertains to. Define what type of coatings you are referring to.

I'm not really sure.., but most mirrors that I come into contact with today use glass before the reflective material. But thank you I already have what I was looking for.

 

[liveforsnow00]

Yeah,
The light as it passes through protective coatings, glass etc would be, technically, refracted.
It is a bit of a nit pick though.

Thanks thats what I was looking for

 

[2inquisitive]

I'm not really sure.., but most mirrors that I come into contact with today use glass before the reflective material. But thank you I already have what I was looking for.

I thought you may have been thinking of a common flat mirror, such as in your bathroom.

Thanks thats what I was looking for

Ah, but your question was about chromatic aberration, not refraction. Let me see if I can quickly explain why chromatic aberration is a specific type of refraction.

Chromatic aberration is caused when different wavelengths (colors) of light pass through a lense. A lense works by refracting (bending) light to focus to a smaller point on a plane. The problem (chromatic aberration) appears because different wavelengths are bent by slightly different amounts as it passes through the lense. For instance, the red wavelength will focus to a different point than the blue wavelength. This focusing to different planes causes the colors observed to appear 'smeared' because the two colors are not both in focus at the same time. That is chromatic aberration.

A mirror in a reflecting telescope serves the same purpose as a lense in a refracting telescope, to focus the incomming light to a smaller point, thus magnifying the image. No chromatic aberration is caused by the mirror as the light is reflected rather than refracted. All reflecting telescope mirrors have the reflecting surface applied to the 'first surface' on the glass, which has a concave shape to focus the light. A coating applied on top of the reflective surface does not serve to focus the incomming light, only to protect the reflecting surface or enhance its reflective properties. It is possible the thin coating could cause a small amount of refraction as light passes through it, but that type of refraction is not chromatic aberration. Hope this helps instead of confusing you.