Sorry guys, but it's probably not a glass prism

Started Sep 5, 2007 | Discussions thread
dkloi Senior Member • Posts: 1,952
Re: Sorry David, but it IS definately a glass prism!!

Abstract of WO2007083661
An infrared radiation is blocked by providing a coating layer (11)
comprising high-refractive index and low-refractive index layers
stacked alternately on a base material (10) in its light incident
face. One of the high-refractive index layers is formed of an ITO
film (11a) to enhance electroconductivity of the surface of the
coating layer. Preferably, the outermost high-refractive index layer
is formed of a transparent electroconductive material from the
viewpoint of imparting electroconductivity to the surface of the
coating layer to more reliably suppress the adherence of dust.
Further, preferably, the sum total of thicknesses of the refractive
index layers provided outside of the high-refractive index layer
formed of the transparent electroconductive material is not more than
140 nm.

I actually think it just means that the third layer (sandwiched in
between the other two) is the Indium Tin Oxide layer which they use
in the "anti-dust" system. Otherwise, it seems to be a conventional
IR filter/low pass filter.

Slight edit: Looking at the patent (unfortunately it's in Japanese so I can only look at the abstract and the figures), the ITO layer is the outermost one. It also seems to be just an IR blocker. Although the patent is called an Optical Low Pass filter, I don't know whether it actually performs that function. It's a high pass filter in terms of frequency of light, and the layer seems too thin to act as a spatial filter (100-300nm).

As ever, Daniel, your patent detective work is valuable!

They seem to imply the three layers does more moiré reduction. I
reckon their language is often not very carefully considered.

If I had been writing up what this camera can do, and what is its
USP, I would have made far more of it than Sony appear to. They have
the old Minolta hang-up of being obsessed with little unique details
they are proud of, and missing the big picture in the process!

Well, there is one way of decreasing moire and not losing too much resolution and that is by a frequency dependent optical low pass filter. If the red and blue components can be smeared more than green, then chroma spatial resolution is sacrificed in return for better moire resistance but luminance resolution would be less affected. It'll come down to actually testing the cameras to see just how well they have designed the AA filter.

Cheers,
Daniel.

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