Focussing a mousetrap style camera
These little cameras were named 'mousetrap' cameras by Talbot's wife as they were found lying all over the house. These are the same style, if somewhat larger, as the camera used to take the famous picture of the oriel window.
This image shows the focussing technique - you remove the cork bung from the hole on the front and look in at the image being projected onto the paper (exposure times are about 4-6 hours so there's no huge risk of the image spoiling!). The lens is a simple plano-convex type fitted into a brass tube that itself is just friction fitted into the wooden box. Focussing is just pushing that in and out!