Hello, I have found the backdoor position may have affect on the proper focusing (amount of the force of the pressure plate).
Prerequisition: mirror and focusing screen are properly calibrated, lens set on infinity stop - you see focused/sharp image of a very far objects (in infinity) in the viewfinder but front focus issue still persists (front focus - optical distance between "lens" and focusing screen is shorter than the distance between "lens" and the film plane // visible focused object on the focusing screen but focus on the film is on nearer objects).
I have two Pentax 67 bodies and have found there was difference in position of the closed backdoor - on the camera body with focus OK the backdoor is "more closed" - closer to the film, so it increases the force of the pressure plate more than the backdoor of the second misfocusing/frontfocusing camera body where the closed position of the door is about 1mm further from the film plane.
The second misfocusing/front focusing camera body had lightseals in the backdoor in whole length - probably added by some serviceman but originaly there is not lightseal in whole length in the backdoor (originaly only about 2cm by the door hinge side). This causes the door to be pushed away from the body/film plane --> less force of the pressure plate (so I have removed back door light seal partialy).
You can also carefully use force to shape/bend the door into the correct position - for increasing force of the pressure plate.
Already tested - film scanned, checked, focusing OK, no light leaks
Note:
Back focus - here the opposite process can help - increase the distance of the door from the film plane - lower force of the pressure plate.
Note2:
0,5mm (max 1mm) thin light seal should be in the camera body, not in the backdoor
Prerequisition: mirror and focusing screen are properly calibrated, lens set on infinity stop - you see focused/sharp image of a very far objects (in infinity) in the viewfinder but front focus issue still persists (front focus - optical distance between "lens" and focusing screen is shorter than the distance between "lens" and the film plane // visible focused object on the focusing screen but focus on the film is on nearer objects).
I have two Pentax 67 bodies and have found there was difference in position of the closed backdoor - on the camera body with focus OK the backdoor is "more closed" - closer to the film, so it increases the force of the pressure plate more than the backdoor of the second misfocusing/frontfocusing camera body where the closed position of the door is about 1mm further from the film plane.
The second misfocusing/front focusing camera body had lightseals in the backdoor in whole length - probably added by some serviceman but originaly there is not lightseal in whole length in the backdoor (originaly only about 2cm by the door hinge side). This causes the door to be pushed away from the body/film plane --> less force of the pressure plate (so I have removed back door light seal partialy).
You can also carefully use force to shape/bend the door into the correct position - for increasing force of the pressure plate.
Already tested - film scanned, checked, focusing OK, no light leaks
Note:
Back focus - here the opposite process can help - increase the distance of the door from the film plane - lower force of the pressure plate.
Note2:
0,5mm (max 1mm) thin light seal should be in the camera body, not in the backdoor
