I have a ADVC300 Canopus Capure Device and I want to convert some older VHS movies that I have to DVD before they wear out. Every time I try to capture them the picture turnes considerably darker about 5 seconds into the capture process. Tried some other tapes which work fine. Why do some VHS tapes record properly and others darken during the recording process. I adjust the brightness in the Canopus editing software but when I save it doesn't stay that way very long. You can see the picture but it's really dark. Any suggestions. Thanks.