When I had my D200 converted to (deep) IR I nearly immediately noticed that the tonal range was significantly less than usual. I was shooting RAW to make sure I captured all the data, but when I got it back to the computer it was totally unnecessary since the histogram showed the image was neither stressing the top nor the bottom of the possible 8-bit range, much less the 12 bits or so that the D200 could normally capture.
That didn’t make me real happy, but when I tried to tone map a single image in Photomatix, the limited data really became evident:
D200(IR), RAW, ISO 100, F8, 1/40
The banding in the clouds at the top is the proof of the narrow tonal range. The range of IR is there, but just not captured in a single narrow tonal range image, as is evident when multiple bracketed images are used with similar tone mapping settings on an true HDR image:
D200(IR), ISO 100, F8, 1/40±1 stop, 3 frame HDR
No banding or any evidence of too narrow tonal range.
So, I’ve learned that with the D200(IR) I need to bracket at least three exposures to get an adequate tonal range for tone mapping. Not sure why one exposure won’t capture a full range of data…