Has anyone used the DG-2 on their D50 or D70 for critical focus? I understand it only allows seeing the center of the viewfinder, but this may not be a problen just for focusing manually. I did a search, and read the thread on DK-21 and DG-17's. I think I am wanting a little bigger image to aid critical focus. If you have any experience with the DG-2, I would appreciate hearing your opinions.