The Paterson microfocus viewfinder is invaluable for producing sharp enlargements as it provides a highly magnified image that can be easily focused. Magnifies 8 times. Sufficient for good focusing.
The grain pattern of the microfocus viewfinder is so bright and clear that it allows focusing at the working aperture to avoid shifting the focus when stopping down. With the 20x grain focus finder you can see the grain better, but often you can't see where you are in the picture.
It also has an adjustable eyepiece that can be calibrated for individual differences in vision.
The microfocus viewfinder has a built-in sliding shutter to protect the mirror and a rubber protective cap to keep the eyepiece clean when not in use.