Pre-Photography

  It is becoming increasingly difficult to find pre-photographica and if a camera obscura does come on offer the price is usually exceedingly high. An inexpensive way of aquiring a camera obscura for one´s historical collection is to build it oneself. It need not coast more than £40 and it is pleasant enough job if one has access to a carpenter´s workshop and metal lathe.

Pre-Studies

First I studied the construction of the camera obscura. amongst others, an example in there is,  the photographic museum in Herning, Denmark and other in the Science Museum in London. The focal point is reached by sliding the inner box in and out until the best definition is obtained. The lens is usually bi-convex and mounted in a turned wooden tube. Some are rigid others are moveable to enable the focus to be adjusted. Later examples may be mounted in brass. The combination of brass and mahogany is often an aesthetical experience and is the reason why I chose them for mine. In 1812 Wollaston used a meniscus lens and obtained better definition. The size of a camera obscura can vary. In Michel Auer´s catalogue one example is reported being 285 x 155 x125 mm. These measurements fit the later meniscus lens of 330 mm. Presumably there are no two early camera obscura which are alike; for that reason you can choose the particular solution which suits you best. This example is not a replica of any existing object but rather a camera obscura which might have been built in the beginning  of the nineteenth century by a village carpenter in England.  

The most common kind of wood used in camera obscuras are walnut and mahogany, but  pine occurs and probably even oak. You can find a pice of mahogany in a wood store or timber yard. The piece I bought measured 740 x 470 x 25 mm. It was allowed to dry out slowly in a bed of sawdust for a month.
A mirror 127 x 137 mm, and a piece of clear glass 127 x 127 mm, were bought at a glazier´s shop. Alternatively you can use a piece of ground glass. The glazier can grind a piece for you. At a junk market I bought a pair of old spectacles with round lenses. The strength of the lenses was three dioptres which is the equivalent of 330 mm focal length. Furthermore I bought a little wooden box from which I utilised the hinges and the lock hook.

The construction

The mahogany wood was split and planed down to 7 mm. The two slide shields lie inside the box but they can also lie on the outside. A plate spring was placed between the shield and the wall of the box so that the lid does not fall down when open. The inner box is joined to ensure good measurement stability. Both dovetail and straight joints were used. Two small hinges allow the lid to open. A long hinge is also common to prevent the light getting in. Both these constructions were to be found at the beginning of the nineteenth  century. One important detail is the bevelling on the front edges. It facilitates sliding the inner box in and out. A lock-hook was attached to the back gable to enable locking the lid.