If the Crizal+UV coating Blocks UV, how does Transitions lenses darken under it?

[Ori]

I would love a good explanation on this.
thanks.

[Robert_S]

Me too

[Lelarep]

It doesn't block the UV wavelength that triggers the transitions lenses to darken?

[jpways]

The UV coating on Crizal is backside only so that UV light can't bounce off the back surface of the lens and back into the eye and is instead absorbed into the coating. Therefore, the front side UV light that activates Transitions is still able to pass through unimpeded.

[AngeHamm]

The UV coating on Crizal is backside only so that UV light can't bounce off the back surface of the lens and back into the eye and is instead absorbed into the coating. Therefore, the front side UV light that activates Transitions is still able to pass through unimpeded.

+1. All Crizal UV treatments are backside coatings designed to eliminate reflected UV. I'm not saying it makes a ton of sense, just telling you what I know.

[Chris Ryser]

Very simple solution: =======> send in some UV light and measure what comes out on the other end.

[jpways]

Very simple solution: =======> send in some UV light and measure what comes out on the other end.

.
Even if this is a 1.50 Plastic lens would that show anything?
Since it's Transitions it should have 0% UV transmission, independent of whether there is a Crizal coating or not (assuming that Transitions advertising is completely correct and it absorbs 100% of UVA and UVB).

[Uncle Fester]

When Big E introduced the "Backside UV" a few years ago I recall at least one lively discussion about how the UV protection is not necessarily in the coating but that because the AR is on the back surface light now passes through the back and out the front surface.

Anyone else remember this and was it debunked?

Couldn't find it in my quick search but it does stand out as a beware of marketing!!!

The light has to be reflected. An old spectral transmission chart from Opticampus and the dirty little UV transmission secret on most materials-

http://www.opticampus.com/tools/tran...e.php?number=0

[Uilleann]

If memory serves, Crizal made the change as they found that most (all?) previous designs of AR on the back of a lens actually reflected UV frequencies. On the front surface: advantage. On the back surface (most always concave), this could somewhat concentrate reflected UV and direct it back towards the eye and adnexa. Hence, they altered their stack to minimize the backside UV reflective properties. Win.

Then, everyone and their dog ran to catch up with their own AR.

[Chris Ryser]

.

Even if this is a 1.50 Plastic lens would that show anything?
Since it's Transitions it should have 0% UV transmission, independent of whether there is a Crizal coating or not (assuming that Transitions advertising is completely correct and it absorbs 100% of UVA and UVB).

Lens materials:

Glass: Crown glass
Flint

Plastic: CR39
Polycarbonate
High index materials

UV transmission in plastic materials is stopped by UV absorbers that work at different wavelengths from 280 nm to 400 nm. Polycarbonate does all of it. CR 39 depending on what absorbance you want.

[Uilleann]

Uh.....

Transmission and reflection be DIFFERENT yo.

[Chris Ryser]

Uh.....

Transmission and reflection be DIFFERENT yo.

Correct ........................

However AR coatings do not reflect 100% of the light hitting the surface, they are reflecting a small percentage to eliminate small visible reflexes on the surface.

The large majority of light rays still goes right through the coating, the lens and transmits them right into the eye. Therefore you still need absorbance of unwanted rays in your lens material.

AR coatings are not the answer to all problems, they are more of a cosmetic patch for the ones who like it and have the money to pay for it.

If you really want a do it all Anti-Reflex surface get a full fledged mirror coating.

[Uilleann]

Sorry - you completely missed the point of the lens the OP asked about.

[golfnut]

Correct ........................

However AR coatings do not reflect 100% of the light hitting the surface, they are reflecting a small percentage to eliminate small visible reflexes on the surface.

The large majority of light rays still goes right through the coating, the lens and transmits them right into the eye. Therefore you still need absorbance of unwanted rays in your lens material.

AR coatings are not the answer to all problems, they are more of a cosmetic patch for the ones who like it and have the money to pay for it.

If you really want a do it all Anti-Reflex surface get a full fledged mirror coating.

Am I missing something here? AR coatings are not applied to REFLECT light but to allow light to pass through by way of reducing internal reflections..It is definitely not just a cosmetic patch for the rich....but I'm sure you know this??

[Chris Ryser]

An anti reflective or anti-reflection (AR) coating is a type of optical coating applied to the surface of lenses and other optical elements to reduce reflection. In typical imaging systems, this improves the efficiency since less light is lost. In complex systems such as a telescope, the reduction in reflections also improves the contrast of the image by elimination of stray light. This is especially important in planetary astronomy. In other applications, the primary benefit is the elimination of the reflection itself, such as a coating on eyeglass lenses that makes the eyes of the wearer more visible to others, or a coating to reduce the glint from a covert viewer's binoculars or telescopic sight.

I know all that, learned it when I got my first LEICA IIIc camera with a coated Elmar lens and still own the last Leica Reflex ever made that has not seen a 35mm film in 20 years.