I totally agree Ryujii. However even though the image on my viewing screen isn't razor sharp, it is very easy to determine the point that it is the sharpest it can be (as one turns the focus knob). That point by definition is when the object is in focus.
Originally Posted by Ryuji
My problem isn't that the image in the viewing screen (via the viewing lens) isn't sufficiently sharp. My problem is when that image is as sharp as it gets, the corresponding image in the film plane (via the taking lens) isn't as sharp as it can get. I have to move the main lens assembly back and forth by about 0.6mm (focus knob turns about 2mm circumferentially) as I switch between looking at the film plane and the viewing screen to ensure each is at its sharpest.
I'm impressed that TLR camera manufacturers were able to manufacture their cameras to sufficiently high precision to ensure appropriate lens and image alignments in the first place.