Editing Camera lucida (section)

==Description==
[[File:cameralucidadiagram.png|thumb|Optics of [[William Hyde Wollaston|Wollaston]]'s ''camera lucida'']]
The name "{{lang|la|camera lucida}}" (Latin for 'light chamber') is intended to recall the much older drawing aid, the {{lang|la|[[camera obscura]]}} (Latin for 'dark chamber'). There is no optical similarity between the devices. The ''camera lucida'' is a lightweight, portable device that does not require special lighting conditions. No image is projected by the ''camera lucida''.{{citation needed|date=April 2023}}

In the simplest form of ''camera lucida'', the artist looks down at the drawing surface through a glass pane or half-silvered [[mirror]] tilted at 45 degrees. This superimposes a direct view of the drawing surface beneath, and a [[reflection (physics)|reflected]] view of a scene horizontally in front of the artist. This design produces an inverted image which is right-left reversed when turned the right way up. Also, light is lost in the imperfect reflection.{{citation needed|date=April 2023}}

Wollaston's design used a prism with four optical faces to produce two successive reflections (see illustration), thus producing an image that is not inverted or reversed. Angles ABC and ADC are 67.5° and BCD is 135°. Hence, the reflections occur through [[total internal reflection]], so very little light is lost. It is not possible to see straight through the prism, so it is necessary to look at the very edge to see the paper.<ref name="hockney-2006">{{Cite book |last=Hockney |first=David |title=Secret Knowledge: Rediscovering the Lost Techniques of the Old Masters |publisher=Thames and Hudson |year=2006 |isbn=9780500286388}}
quote  {{cite book
 | last= Wollaston
 | first= W. H.
 | title= Description of the camera lucida
 | work= A Journal of Natural Philosophy, Chemistry, and the Arts
 | year= 1807
 | publisher= William Nicholson
 | url= https://books.google.com/books?id=AeA3AQAAIAAJ&dq=Wollaston,+W.+H.+(1807).+%22Description+of+the+camera+lucida%22.+A+Journal+of+Natural+Philosophy,+Chemistry,+and+the+Arts&pg=PR4
 | access-date= April 26, 2023
 | archive-date= April 26, 2023
 | archive-url= https://web.archive.org/web/20230426200035/https://books.google.com/books?id=AeA3AQAAIAAJ&dq=Wollaston,+W.+H.+(1807).+%22Description+of+the+camera+lucida%22.+A+Journal+of+Natural+Philosophy,+Chemistry,+and+the+Arts&pg=PR4
 | url-status= live
 }}</ref>

The instrument often came with an assortment of weak negative lenses, to create a [[virtual image]] of the scene at several distances. If the right lens is inserted, so that the chosen distance roughly equals the distance of the drawing surface, both images can be viewed in good [[focus (optics)|focus]] simultaneously.{{citation needed|date=April 2023}}

If white paper is used with the ''camera lucida'', the superimposition of the paper with the scene tends to wash out the scene, making it difficult to view. When working with a ''camera lucida'', it is often beneficial to use toned or grey paper. Some historical designs included shaded filters to help balance lighting. {{citation needed|date=April 2023}}