Originally Posted by Murray@uptowngallery
This story of the heated cloth iron, even without cloth, is so old that it already in literature from the seventies was stated as a tale.
Walter already hinted at that infrared photography based on halide materials is mainly about recording differences in IR-reflection. Not about recording of differences of IR-radiance due to temperature differences.
Objects with a temperature higher than 525°C have a visually different appearance (glow). Objects with temperatures below 250°C would have to be exposed unfeasibly long on IR-films. (By the way, the maximum temperature of a cloth iron is something of 230°C...). I have seen a photograph of a heated solding iron, but still exposed extremely long.
The Wood effect (R.W. Wood) is nothing but a vast overexposure of leaves combined with a blocking of the rest of the object by means of an IR-filter. That overexposure is due to the reflection of IR-radition (typically from the sun) of the leaves. The lowerside of leaves is highly reflective (like snow etc.) but is covered with clorophyll with a high absorbtion in the visible spectrum (bands at 450 and 670nm), thus acting as an IR- filter. This reflection is dependend on the sort, the vegetation period, but also on the health of a tree. (Also think of autumn colours.)
Fields of scientic/commercial use are/were agriculture, medicine, forensic, history of arts.
Concerning aero survey: there are a lot of very small businesses in that field who are not likely to change to a camera system based on digitally recording due to the inherent investments. Those will remain using film.
Last edited by AgX; 07-05-2007 at 08:45 PM. Click to view previous post history.