What an optical coating does
An optical coating is a thin layer, or a stack of thin layers, applied to an optical element to control what happens to light at its surface: what is transmitted, what is reflected, and what is blocked. Interference filters are built from such coatings, which is why coating behaviour decides filter behaviour. A coating guide at category level therefore covers concepts rather than values: transmission, reflection, blocking, and the way a coating stack creates a pass band or a cut-off edge. Values belong to a specific product, and on this site documented coating values exist only for fluorescence filters.
The documented coating evidence
For fluorescence filters, the documented coating process is IAD hard coating. That statement is attached to fluorescence filters on the fluorescence filters page, with its blocking and slope figures. It is not presented here as a general coating specification for other lines, and buyers should not read it as one. For every other line, this guide stays at category level: it explains what coatings do, and it asks buyers to confirm the coating requirement for their product in the inquiry. Equipment names listed by the company are Optorun OTFC 1300 and Leybold Syrus 1350 automatically operated coaters, and Cary 5000 and Cary 7000 high performance spectrophotometers. Those are equipment names only; no photograph on this site is presented as a photograph of that equipment, and no coating machine photograph is published.
Coating concepts buyers should know
Transmission describes how much light in a wanted band passes through. Reflection describes how much light is sent back. Blocking describes how strongly light outside the wanted band is kept out, often expressed as an optical density figure. Slope describes how steeply transmission changes between a pass region and a blocked region. Cut-off depth describes how completely a blocked region is suppressed. Each concept matters differently by application: a fluorescence application cares deeply about blocking and slope, because weak emission must be read against strong excitation; an attenuation application cares about even reduction across a range; a reflector application cares about reflection in its working region. Naming the concept you care about, with the wavelength region it applies to, makes an inquiry far more checkable than asking for a coating in general terms.
What to confirm in your inquiry
Please confirm the following items in your inquiry before ordering: the coating job your element must do; the wavelength region it applies to; the transmission, reflection, or blocking behaviour you need in that region; the size and substrate material; and the quantity basis and delivery basis for your order. For coating background in note form, see the optical coating basics note.