After the paint had dried on the inside, I took the camera out for a test.
The 0.3mm pinhole has an effective aperture of f/200 for the 60mm focal length. This gives an exposure of 10s with +1 stop for reciprocity failure compensation.
Which I timed on my phone.
And then used the ‘Massive Dev Chart’ app to help with the development (awesome app, you should get it). I processed the 4x5 sheet film (Shanghai Pan 100, aka ‘GP3’) in Rodinal at 1:49 dilution.
I normally print my negatives, so wasn’t setup to take a scan (photo) of a 4x5 negative. I placed the negative on my tablet computer. This resulted in a bit of a weird image (as you can see the pixels) but was good enough for a test.
With the image inverted in GIMP. The grey area on the left is an inverted white reflection of my ceiling. Good enough for a test. Looks like I needed to add more reciprocity failure compensation.