Actually you are not “capturing” in the original sense like analog. You are simply making a bit-for-bit copy of the file that is already on the tape. So your “capture” is already completely lossless because it is a digital copy.
What are you using to determine quality? I would output a small section of your footage out to Blu-ray or DVD and watch it on an HD TV. If it looks OK, then the problem is with your PC monitor not being calibrated correctly or possibly that your monitor can’t display these files at full resolution so it is scaling the footage. If you PC monitor is not capable of displaying 1920×1080 then this will add to the problem. Nothing to worry about since it will not affect the final output.
~jr
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