I have been looking for optical reflectance properties of black anodized aluminum finish. No luck so far.
Does anyone know about it or could help me find where to look?
The reflectance of the finished surface is highly dependent on the surface preparation. I've seen anodizing that's fairly shiny and others that were very diffuse.
In the past I've had surfaces bead blasted for anti-relection properties, this has worked very well and quite cost effective on imaging/low power laser systems. Also, I've had surfaces polished before anodize and used them as a beam/light dump in imaging systems when used with an internal lighting system i.e coaxial illuminator. So it is totally dependent upon the requirements of the system as to what form of reflectivity one needs.
It depends on the surface finish of the item to begin with. Then the selected pretreatment, this could be a satin etch to a bright-dip (a hot mixture of phosphoric and nitric acid with a little copper sulfate). It can be very bright to almost completely dull depending on the skill of the processing shop.