When capturing DV/DVCPRO50 through IO/IoLA, video scope in Log & Capture window displays erroneous luminance readings. Tool bench video scope showing playback levels is accurate, agreeing with external waveform monitor. No discrepancy exists with uncompressed codec.
Discrepancy appears to be gamma -related, as it is worst (approaching 10% lower than actual level) at mid-range values.
Substituted IoLA with a consumer-grade video-to-FireWire converter and observed no discrepancy, using DV-NTSC Easy Setup.
Same behavior has been observed over multiple systems running a variety of hardware, on both FCP 5 & FCP 6.