Rule of Thirds Gauge

We're all familiar with the rule of thirds, and how we can use it when composing a shot or in the darkroom to elevate a photograph to a masterpiece. I've been finding it very tedious having to measure thirds in the darkroom with a ruler, or cutting appropriately-sized pieces of paper with lines drawn to mark the thirds. I've found an elegant solution to this problem that is both easy to DIY and is adaptable to all sizes of paper.

Inspired by the golden ratio gauges often constructed and used by woodworkers, I took pen to paper to conceptualize what a similar gauge would look like when constructed to give three equal sections. Here are my initial scribblings:

A quick sketch lays out the unit lengths for each arm of
the gauge. Three units for each long arm, two units for
the short arms.

The idea was simple enough, and to my surprise, it was even easier to construct a functional prototype. I sort of brute-forced the solution with super simple math, working with a unit length of 9cm. I'm sure there is a mathematical proof that shows why this device works, but I'm happy enough having sorted it out so simply. The two long arms are 27mm from the pivot point to the tip, and the two short arms are 18mm from their pivots to the tip. All pivot points are 9cm apart. These lengths can of course be adjusted for any sized gauge you wish to construct, as long as the ratios stay the same. Here is a photo of my prototype, made of cardboard and complete with toothpicks to hold everything together:

The gauge functions by first adjusting the two outer points to the desired dimension. When set, the two inner points will show the exact lines that divide the paper into three sections. Easy thirds, without a ruler!

For the final product, I took some black matboard and cut it into 1" strips. I drilled holes with the four pieces clamped together so the holes would be exactly the same on all pieces. The ends were cut to points, and brass brads were used to hold the whole contraption together.

Simplicity, ease of construction, and versatility, this gauge has it all. So far it's proven to be extremely valuable in the darkroom, and I hope to see others start using this tool as well!

Exposure Considerations for the Holga Wide Pinhole Camera (120WPC)

I love the Holga 120WPC. It's lightweight, easy to use, and can yield awesome results in 6x9 or 6x12 formats. It does however have a significant drawback, which is related to focal length and negative size. The focal length (the perpendicular line from the pinhole to the film plane) of this camera is approx. 40mm, but with the 6x12 mask in place the edges of the negative are much farther away from the pinhole than 40mm. I'll illustrate:

The labeled f-stop on the 120WPC is f/135, but as I've shown in my calculation above, the effective f-stop at the edges of a 6x12 negative is f/240. This gives an approximate exposure difference of two stops from the center to the edge. This is a noticeable difference, perhaps not for those who are scanning film, but indeed so for those of us who print in the darkroom. 

Interestingly, this 2-stop exposure difference is retained, regardless of exposure length. Using the exposure suggestions on the back of the 120WPC, I assigned Exposure Values (EV) to each and made exposure calculations, correcting for reciprocity failure where needed:

The recommended exposure times on the
back of the Holga. I assign EV 15, 13,
and 11 to these weather descriptions.

Even when accounting for reciprocity failure (in this case, using P=1.15 for TMax100 film), the adjusted exposure for the edges of the film is approximately 4 times (2 stops) greater than at the center. It's nice knowing that we don't need to make more complex calculation on-scene when using this camera.

With these calculations in mind, we can strategize when using his camera, to either use this shortcoming to our advantage, or selectively place bright subjects off-center so they don't wind up unnecessarily over-exposed. I'll show some example photos of mine below, and caption them with some discussion and explanation.

This photo is scanned from a darkroom print. I slightly dodged the edges to lighten them a bit, but they are still much darker than the middle. In this case, with the sun shining through the trees in the middle, I like the effect and don't mind the dark sides.

A scanned negative. Again, a bright subject placed centered in the frame gets extra exposure and is exaggerated. I think this characteristic of the camera works to great effect here.

Other considerations when shooting with this camera include keeping track of light sources. In most cases, having the light source behind the camera gives the best chance of success. Sometimes though, having the sun in-frame can yield interesting results:

A unique artefact of direct sunlight interacting with the pinhole. Not a bad effect; I was pleasantly surprised seeing this come out of the development tank. This photo is a scanned negative.

On the other hand, sometimes the sun will accidentally shine through a scene, creating unintentional and undesirable flare on the film:

Here, the sun is obviously out-of-frame, but it was shining onto the pinhole nonetheless. The resulting flare spoils the photo for me, so this negative isn't likely to see any action in the darkroom.

In my experience, the only way to be completely sure to avoid these light flares, is to point the camera completely away from strong light sources. I may try modifying a hood that could fit on the camera someday.

I hope this deep dive into the nuances of the 120WPC was of interest! As always, I encourage discussion and very much welcome feedback.