I have experienced the same with other cameras as well as other formats. The bottom line is that the camera needs to clearly see some surface feature in order to provide the correct focus and the camera will not take the picture until it does. I have had this problem in other lighting conditions trying to shoot very smooth surfaces. You will also have this problem if you try and get too close to a surface without a macro lens.

Your scenario seems to be occurring due to lack of light. The obvious answer is to provide some lighting on the exterior or interior surfaces. If electrical power is available, then a simple and cheap work lamp would do the trick. In cases where no power is practically available, we generally carry a small Honda generator that is capable of running one to two work lamps. I was at a small fire scene with a number of experienced investigators and they seemed more impressed and wanting to talk about this small generator than anything else. I remember it being somewhat expensive, but it has been worth the cost. We also carry lots of extensions cords to keep the generator far from the boundary of the fire scene.

Douglas J. Carpenter, MScFPE, CFEI, PE, FSFPE
Vice President & Principal Engineer
Combustion Science & Engineering, Inc.
8940 Old Annapolis Road, Suite L
Columbia, MD 21045
(410) 884-3266
(410) 884-3267 (fax)
www.csefire.com