A Mousetrap camera.

When conducting his early experiments, William Henry Fox Talbot used a number of very simple cameras,  little wooden boxes which he positioned around his home, causing his wife to nickname them his “mousetraps”. 
Talbot started by using the lenses he had to hand -generally from microscope optics. These typically have tiny coverage and short focal lengths, hence the small boxes. 
This one was made as an experiment after I was given a tiny lens, possibly from a microscope or something similar.. The focal length is about 33mm and the maximum aperture is approx. 16mm  which equates to f/2. 

The "Nipper" mousetrap camera. about 3 inches (8cm) high.

A basic box was made up from plywood with the lens simply screwed into a hole in the wood. The back is hinged with a hook catch to hold it shut.  More pieces of plywood inside make a frame to hold the plate / film / paper in the right position for an infinity focus. Such tiny lenses are hard to focus accurately but by trial and error with a piece of ground glass and a magnifier the frame was sanded down until it was the right depth. Closer distances could be focussed by the addition of card spacers.  

Loading in the darkroom. The paper neg here is a little under 60mm x 70mm.

Made for experiments with early processes such as Talbot’s salted paper Calotype it’s about as simple as a camera can be and makes a very beautiful image on tiny plates. The whole camera is about 3 inches (8cm) high.  It has a tripod bush but no shutter or viewfinder and no removable plate holder. The camera is loaded and unloaded in the darkroom for each shot.

Here are some preliminary tests using little bits of resin coated print paper:

Like Niépce (and because it was raining) I started with the view from my window. You can see the reflection of the tripod. 

Note how the centre of the image is reasonably sharp but  the distortion rapidly increases towards the edges. All lenses do this, but mostly the camera just uses the 'sweet spot' in the middle. I deliberately made this oversize to explore the effects.

Liss Mill. Opposite my house it's a handy test subject.

Without a viewfinder, aiming the camera is a bit hit and miss. I could set it up with ground glass in place but then I'd need to return the camera to the darkroom for loading. A quick release tripod plate would be a solution. A better one would be to have made the camera take film holders ('dark slides') but I wanted to keep things simple, primitive and true to the Fox Talbot original.

The lens covers a very wide angle but as only the centre is sharp framing is more critical than you'd expect. In this picture the building is reasonably sharp (you can count the bricks in the central area) because it was well centred...

... This time however it's framed a little closer to the top and the resulting distortion is quite dramatic!  I don't see this kind of thing as a defect of the lens, more revealing aspects of its character.

Another aspect I hadn't worried about was the speed of the lens. At f/2 it will be good for very slow materials like salted paper calotypes but if anything it's a bit too bright for paper negs. 
Exposure times on a dull rainy day were around 1/8th second or so. I was using a Sinar shutter on these tests for accuracy but I want to use just a lens cap to control the exposure. a much smaller aperture, say f/32 would mean long exposures of several seconds or more. - easy to control without a mechanical shutter. I need to make a 'Waterhouse Stop': a piece of thin metal with an aperture hole cut in it. As the f/ stop number is a fraction of the focal length, f/32 for this lens will be about 1mm in diameter.  I'll get lots of depth of field but probably not much reduction in the distortion. We shall see..Finally, as the weather deteriorated and I decided to pack up for the day I noticed the panels of the back door. This is just opposite the darkroom and I've passed it hundreds of times. Today though, with early pioneer photography on my mind I noticed it bore a slight resemblance to Talbot's famous Latticed Window. Time for a little homage...

My back door. Almost entirely unlike:

...Talbot's Latticed Window at Lacock, 1835.

I made the camera as the first step in experimenting with things like Calotypes and other very simple in-camera processes. I've learned a few things which will go into future projects and I've felt about 8 years old, enjoying the excitement of it all. Lenses are miraculous things!

[Finally if you're wondering why the mousetrap camera is named "the Nipper" ask your grandparents! :-)