I agree with others in that the Green channel will give the finest grain with the Epson 4990. but the difference compared to using all three channels is not great. If the issue is scanning LF B&W film in 4X5 or 5X7 size with an Epson 4990 I basically agree with Ken in that the small decrease in grain size one can get by scanning in RGB and using the Greeen channel does not justify the considerable additional scan time and file size compared to scanning in B&W 16 bit, at least not for normal size prints.
For MF negatives that will require a lot more magnification my experience is that there is a clear advantage to an RGB scan, and then selecting the best channel, which is usually Green.
Sandy King
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