The problem with going through old files and negatives is finding forgotten and unidentifiable images. That is exactly what this is, all the negative page said was ‘Pinhole experiments’ with 35mm camera and body cap, it had several badly exposed and/or very blurred images but this one was the best.
I remember reading about the possibility of using a body cap drilled for a pinhole lens, but cannot find the modified cap since moving.
I do remember using the Nikon F4/Nikon F2Sb after making the lens from a drilled body cap which I then fitted with a disc made from very thin aluminium with a precisely centred hole. The ‘f’ stop was around f:200, calculated by using the following.
f-stop = focal length / aperture diameter
Figures estimated by using a ruler and dividers, was about 0.25 mm and the distance of the pinhole to film plane about 50 mm.
f-stop = 50 mm / 0.25 mm = 200.
For those who wondered what the symbol of a circle bisected by a line was on their SLR, it denotes the point of focus for images at infinity; the film plane.
The disc was sanded, cleaned in Isopropyl alcohol then glued onto the lens cap and all painted with matt black paint.
Why I have never carried on with these experiments I have no idea and the memory jog only came after looking at pinhole images posted on Kevin Allan’s excellent blog filmphotography.blog/2019/09/25/ondu-pinholes-hexham-abbey/ Well worth visiting for his images and articles about cameras, materials & techniques.