The 120 format film caused a punch mark on the first or last frame, what’s lab wrong?
It is from camera or film loading, the dip and dunk processor use the hanger hanging the film. The hanger will punch the film in order to hold it both on the leader and the trailer for weight. The punch is actually around the length of 1 inch or less similar to ordinary desk stationery staple. Usually, the film manufacture the standard length which leave some space for leader and trailer. And it looks properly when get the right start.
What is Right Start?
The paper back of 120 film format have the arrow for Right Start mark. Be set this arrow to match the red dot on the camera. Then close the camera back. When winding the film, the camera will automatic start to frame #1 by mechanism gear.
If we close the camera back earlier than the arrow point to the red dot. The first frame will start earlier and be punched. Because the camera mechanism counted frame#1 by winding wheel. This case, the last frame will shown long dark trailer.
On the other hand, if close the camera back after the arrow pass the red dot. The punch will show on the last frame.
The film magazine itself is another issue. Some magazine gear is loose. It makes the gap between one frame to another frame more and more. So the last frame will lost or punched, even get the right start when loading film.
Dip and Dip processor is common used for professional developing. The film will dunk in solution and will raise to the next tank solution when meet the developing time. Not like the consumer machine which is leader belt holding the film and pass the processing roller which might cause straight line scratch.