It was a sunny, but bitterly cold 6 February 2010 when Alex Gabov, Kate Sullivan and I set out to the Cataraqui Cemetery to make our first RTI captures. We had high hopes for two or three captures, but the -20 C temperatures (-4 Farenheit for our friends south of the border) kept us down to a single sequence: the tombstone of David Kemp. In order to keep down the bright sun we erected a large temporary shelter to block the sun on the stone and we lit a propane heater to keep the living humans warm.
All was going well on the first few images until our flash unit or wireless remote unit (we’ll talk about our equipment on a later post) began failing. We just couldn’t diagnose the problem…we consulted manuals but the extreme cold meant exposed finger flipping pages were soon numb. Alex and Kate left me and the propane heater in the cemetery while they went back to the studio at Queen’s to figure out the problem. As so often happens, they texted me to assure me that as soon as the re-entered the studio our set-up began working perfectly. The problem: the cold, pure and simple. Our Opus Four-Channel remote was too cold to transmit and Alex was forced to reheat it every five shots in his work van.
So what would have normally taken us only half an hour in normal conditions took us three frigid hours. The results, however, were worth it:
The Normal Visualization feature in the HP PTM viewer disclosed to us an interesting effect we had not fully anticipated. The lichen growing on the stone cause a serious mis-estimation of the surface normals:
This unintended discovery could have real benefits…the surface normal visualization could be used to determine the lichen covering on a stone before and after cleaning by stone conservators.
At the end of the day Alex seemed unaffected by the cold while Kate and I were desperate to return to indoors and process our images.