Steve Shapiro wrote: > > Light that strikes the film plane is measured in 'Wavelength.' Within the > wavelength is a 'band width' and each color has a temperature along the band > width that effects the photo sensitive material differently. Filters > deflect some sensitivity off the wavelength and compress the most into few > bands within the wavelength. To use a filter or filter pak lets us control > the wavelength, making it even when the light strikes the film plane to make > a picture. This is, umm, how should I put this diplomatically... I think your joke fell flat. I'm sure some people may have taken it seriously. > Light that strikes the film plane is measured in 'Wavelength.' Light isn't measured in wavelength. It has a property called wavelength. That property can be measured. (Distance can be measured in wavelengths -- and often is) > Within the wavelength is a 'band width' No. Bandwidth refers to (typically) a range of frequencies in a transmission. A single photon does not have a bandwidth, because it has a single frequency (which, via C, Einstein, and Relativity) determines the wavelength. A beam of light, or perhaps light from a scene, could perhaps be said to have a bandwidth. > and each color has a temperature along the band width Temperature is a measure of average kinetic energy. Since a single photon has a certain kinetic energy, and there's only one of it, I suppose you could measure a temperature. However I'm not certain that this is related to "colour temperature", which in turn is related to black body radiation. > that effects the photo sensitive material differently. Well, no. A photon will either have an effect, or it won't. There are many factors (including statistical) that determine this. (OK, some effects require >1 electron) > Filters deflect some sensitivity off the wavelength and compress the most into few > bands within the wavelength. Filters don't have any effect on sensitivity (and what does "deflect sensitivity off a wavelength" mean?). They cause some photons to be reflected or absorbed (and therefore not pass through). Changing a filter does not effect the sensitivity of a film any more than it affects the aperture of the lens. If we look at ideal filters, they *may* be characterised as high pass (cyan), low pass (yellow), band pass (green), etc... But in general (and we have to exclude filters with any flourescing screen in them) they don't alter the frequency of any photon. > To use a filter or filter pak lets us control the wavelength, No, it allows us to modify the relative intensity of components haveing different wavelengths. > making it even when the light strikes the film plane to make > a picture. If it made it perfectly even we'd have an 18% gray image. But yes, we may use it to reduce contrast (in b&w) or for colour correction (which is, I assume, what you're talking about here). But we may also use it to increase contrast. Steve
