Eighteen

Eighteen
February 1936. “Mission District. San Francisco, California.” Medium format negative by Dorothea Lange (1895 – 1965) for the Resettlement Administration. – Shorpy

Dorothea used the Graflex Series D to take her photographs. The lens came standard as a f/4.6 anastigmat lens with a focal length of 7-1/2 inches (190mm) – 4×5 camera. If you just take a quick look at this photo you may dismiss it .. that would be an error in my opinion. I decided that it would be cool to try and model this structure .. at least as a low-profile structure and that it might be fun to walk through what I did to bring it back to life in model form.

The Door
The plan was to bring the image into Sketchup where I could scale the building/photo as long as I had one item that I knew the size of. The obvious place to start was the open door. A exterior doors can be 30, 32 or 36 inches wide standard. A typical 6’8″ (80″)door slab pre-bored will have the door knob hole at 36″ from the bottom side.

http://hdl.loc.gov/loc.pnp/fsa.8b13829

The first thing to do was to correct the perspective of the door in the photo. Opening up the photo in Corel PaintShop Pro 2018 I used the Perspective Correction Tool setting the handles on the top and bottom corners. This gave me a door without distortion.

With a corrected door I brought the photo into Sketchup as an image. I could then simply use the Line Tool to trace around the door. I also found the center of the door knob. I added dimensions to width, height of door and height to center of door knob then tried a 30″ and 32″ door.
The 30″ door width. height is close to 81″ but height to center of door knob is almost exactly 36″.
The 32′ door width. The height is 86″ and height to center of door knob is 38-1/2″.
With the knowledge that I am attempting to get measurements from a fuzzy photo (close up) with relatively fuzzy edges I can see that the door width and center height of door knob match almost exactly for a standard 30″ door. The slight excess height I will simply denote inaccurate measurement on my part.
Lumber Size Standards
The following is taken from History of Yard Lumber Size Standards

Lumber size standards came into being almost a century ago to meet the need for a common understanding between the mill and markets that were separated by increasing distances of rail or water transportation. Early concepts called for rough lumber to be of full nominal size, often in the dry condition. After World War I, the increasing demand for construction lumber led to the first national size standard in 1924.

The photo we are attempting to get measurements off of was taken in 1936. Looking at the weathering on the building it could easily have been built c. 1900 .. so a 2″x6″ board may very well be the full 2″x6″ and not the 1-1/2″x5-1/2″ we would find today. In fact .. it could be whatever was needed at the time if cut locally.