Quote Originally Posted by Helen B
. . . But don't we need some way to describe the bright, directional mirror-like reflections from non-mirror surfaces when we want them to record detail? The practical importance of the apparently academic distinction is a result of the assumptions made about the limits to the range of surface reflective index when using an incident meter. 'Specular' reflections may lie outside this range, and we may wish to record detail in them. If we wish to record detail in them an incident meter cannot, on its own, indicate the exposure required because the ratio of incident to reflected light is unknown.

How does that sound?
Yes, I think so, and sounds great.

I think part of the issue here is the technique used in taking the incident reading. The usually-suggested method of pointing the incident dome at the camera tends to under-measure the intensity of light that creates the specular reflections, whereas pointing the incident dome at the light source (i.e. metering the light itself) takes that into account. It's rather like being aware of the solar disc in your peripheral vision versus looking directly at the sun.

The practical problem is that if the light source is the sun, the under-measurement resulting from the usual incident reading technique is extreme, and the light intensity is such that the highlight on film tends to spread/bleed into the surrounding area of the negative due, I believe, to failure of the anti-halation backing. As the print has an absolute maximum white value, the medium can't deal with the excess negative density, so all that is seen is the highlight and its bleed into the surrounding areas.

Although I haven't studied/tried the BTZS metering method, it seems to me that in situations (similar to that Noseoil confronted) that fall outside the usual range anticipated by the method, an additional meter reading needs to be added to the decision matrix - either a spot reading of the highlight, or an icident reading with the dome pointed at the light source (e.g. the sun in this case). Then, how one balances the exposure/development probably depends on which end of the luminence range one wishes to give precedence.