The guys that build huge aquariums said that acrylic used in their tanks is clearer than glass. Acrylic is 97% clear while glass is only 76% clear. Just what is the clarity of lens glass?
Glass designed for use in optical fibers has attenuation lengths measured in kilometers; over the visible spectrum, a kilometer long optical fiber might lose 50% of the light, and lose only 5% at peak transmission in the infrared. Typical "window glass," however, is often already a murky dark green at only a few inches thick. Everything else usually falls somewhere in-between
Talking about "glass" is pretty much the same as talking about "plastic" or "steel". It is a big area of materials science and there are a lot of different glasses out there.
My contribution to this thread stolen shamelessly from Wikipedia:
The majority of photographic lenses have the lens elements made from glass although the use of high quality plastics is becoming more common in high quality lenses and has been common in inexpensive cameras for some time. The design of photographic lenses is very demanding as designers push the limits of existing materials to make more versatile, better quality and lighter lenses. As a consequence many exotic glasses have been used in modern lens manufacturing. Caesium[1] and lanthanum[2] glass lenses are now in use because of their high refractive index and very low dispersion properties. It is also likely that a number of other transition element glasses are in use but manufacturers often prefer to keep their material specification secret to retain a commercial or performance edge over their rivals.
The last sentence captures Canikon's philosophy about lenses.
I had a "killed in a fall" Minolta superzoom P&S. Being curious, I dismantled the lens. I found most of the internal elements were actually plastic rather than glass.
I received a reply from Wayde King of Acrylic Tank Manufacturing. He says that the statement about glass referred to ordinary window glass. Here is the reply.
Is Acrylic clearer than glass? -Making your products and livestock look great and stay healthy
We create product displays, podiums, jewelry cases, and more… -All the way across the board to custom acrylic aquariums that we have created to be placed in professional establishments. As we explore the choice between glass and acrylic, we can’t help but wonder how acrylic materials are so much more clear than glass.
A study of the light that passes through materials has shown that while conventional glass will typically filter out much light including some in the visible spectrum, acrylic resin (Plexiglas) does not. It leaves light untouched for the most part.
Why is this important? If I was using a display case for living plants, or creating a top for a reef aquarium, I would need to be certain that the deep parts of the ultraviolet spectrum are passing through to my plants and animals. Glass may diminish the health of my live stock, and in the case of corals, leave them drab and gloomy.
Light spectrum chart for acrylic vs glassScientists have discovered that while glass will usually start to take much of the visible and invisible light spectrum out, Acrylic / Plexi will not. Acrylic material has the same refraction pattern as water. Glass is all over the place and is simply expensive to engineer it for the spectral output one desires. Please see the chart below to compare Acrylic, Glass, and the light measured on an average (good weather) day. Clearly, we can see how the glass starts to filter out the upper visible spectrum and in other charts can be seen to be unreliable in other parts of the EM spectrum.
It appears one could make lenses of acrylic, but it would pass unwanted parts of the spectrum. runamuck
