Welcome to the second part of the ultra large format camera build. In this part of the project build we are working on the camera back that supports the ground glass and film holder. This has been the most difficult part of the project build so far as the tolerances are very small and all fittings must be strong but light. The film holder proved especially problematical in making sure there was no light leakage when removing the film cover slide. There is a video podcast and a comprehensive series of images detailing part two of the project build so far below.
Ben Dolman and Alan Duncan Large Format Camera Build Part Two from Ben Dolman on Vimeo.
The camera back is fixed to the rear carriage with nine quick release toggle clamps that allow for quick and simple removal of the camera back to reposition it in the horizontal and vertical viewing plane.
Detail of the camera back in the horizontal position
The camera back is made up in two parts, the ground glass frame and back carriage insert. The two parts are held together with 8 extension springs connected to 3 mm thick aluminium angle extrusion with M5 bolts.
The ground glass frame has a fabric strip to cushion the ground glass that can be prone to shatter in large format cameras, additional wooden beading will be used to fix the glass into position that will have a rubber seal to cushion the glass during transportation and the opening and closing of the ground glass frame when inserting the film holder.
Film back in the open position, the ground glass frame is released by a large pivoted lever that is off set to extend the springs.
A close up view of the pivoted lever with the ground glass frame extended out. At the moment the lever has a ABS runner but this will be replace with a thin nylon plate which will be smoother. There will be a catch to lock off the lever so it does not move when the film holder is being inserted.
The film holder will be able to hold negatives and photographic paper up to 20" x 24" and can also be adapted as a reducer back to take smaller media.
The film holder is constructed from cherry wood, aluminium extrusion and ASB plastic. The chief goal was to build the film holder as light as possible but strong and there was no light leakage.
The ground glass frame extends out to about 50mm to allow plenty of play for the 40mm depth of the film holder to be inserted with no force required so as not to move the camera which is critical.
Film holder inserted into the camera back
Detail of film back
The film holder is held in position on 3 sides with 2" x 2" aluminium extrusion on the longest sides and a smaller extrusion at the end with a wooden plate to guide the ground glass frame when extended and also to lock the lever in position when not used.
Moving the cover slide out of the film holder
The film holder has a 3mm aluminium bar that is used to contain a spring shutter to stop light leakage when the film cover is removed, the bar is also used to lock the film holder in position into the camera back
Sliding the film holder out of the camera back
Detail of the offset lever with the film holder in the vertical position, this was the first design that has now been changed to be flat on one side to help lock the lever in the open position.
Stage two completed now for ground glass and bellows
No comments:
Post a Comment