The precursor of the modern camera, the camera obscura is a darkened enclosure into which light is admitted through a lens in a small hole. The image of the illuminated area outside the enclosure is thrown upside down as if by magic onto a surface in the darkened enclosure. This technique was known as long ago as the fifth century B.C. in China. Aristotle also experimented with it in the fourth century B.C., and Leonardo da Vinci described it in his notebooks in 1490. In 1558 Giovanni Battista Della Porta wrote in his twenty-volume work Magia naturalis (meaning "natural magic") instructions for adding a convex lens to improve the quality of the image thrown against a canvas or panel in the darkened area where its outlines could be traced. Later, portable camera obscuras were developed, with interior mirrors and drawing tables on which the artist could trace the image. For the artist, this technique allows forms and linear perspective to be drawn precisely as they would be seen from a single viewpoint. Mirrors were also used to reverse the projected images to their original positions.

Did some of the great masters of painting, then, trace their images using a camera obscura? Some art historians are now looking for clues of artists' use of such devices. One of the artists whose paintings are being analyzed from this point of view is the great Dutch master, Jan Vermeer, who lived from 1632 to 1675 during the flowering of art and science in the Netherlands, including the science of optics. Vermeer produced only about 30 known paintings, including his famous The Art of Painting. The room shown in it closely resembles the room in other Vermeer paintings, with lighting coming from a window on the left, the same roof beams, and similar floor tiles, suggesting that the room was fitted with a camera obscura on the side in the foreground. The map hung on the opposite wall was a real map in Vermeers possession, reproduced in such faithful detail that some kind of tracery is suspected. When one of Vermeer’s paintings was X-rayed, it did not have any preliminary sketches on the canvas beneath the paint, but rather the complete image drawn in black and white without any trial sketches. Vermeer did not have any students, did not keep any records, and did not encourage anyone to visit his studio, facts that can be interpreted as protecting his secret use of a camera obscura.

In recent times the British artist David Hockney has published his investigations into the secret use of the camera obscura, claiming that for up to 400 years, many of Western art’s great masters probably used the device to produce almost photographically realistic details in their paintings. He includes in this group Caravaggio, Hans Holbein, Leonardo da Vinci, Diego Velazquez, Jean-Auguste-Dominique Ingres, Agnolo Bronzino, and Jan van Eyck. From an artist’s point of view, Hockney observed that a camera obscura compresses the complicated forms of a three-dimensional scene into two-dimensional shapes that can easily be traced and also increases the contrast between light and dark, leading to the chiaroscuro effect seen in many of these paintings. In Jan van Eyck’s The Marriage of Giovanni Arnolfini and Giovanna Cenami, the complicated foreshortening in the chandelier and the intricate detail in the bride’s garments are among the clues that Hockney thinks point to the use of the camera obscura.

So what are we to conclude? If these artists did use a camera obscura, does that diminish their stature? Hockney argues that the camera obscura does not replace artistic skill in drawing and painting. In experimenting with it, he found that it is actually quite difficult to use for drawing, and he speculates that the artists probably combined their observations from life with tracing of shapes.

现代相机的前身——暗箱是一个密不透光的箱子，箱子上有一个带着透镜的小孔，光线由此射入。来自箱外接受光照的图像如同被施了魔法一般，在这个密不透光的箱子内壁上构成倒影。暗箱技术最早可追溯至公元前五世纪的中国。公元前四世纪，亚里士多德曾进行相关实验；1490年，列奥纳多•达芬奇也曾在他的笔记本中描述了这一现象。1558年，乔瓦尼•巴蒂斯塔•德拉波尔塔在他长达二十卷的作品Magia naturalis（意为“自然魔术”）中介绍，增加一个凸透镜可以改善倒映在暗箱的帆布或画板上的图像质量，就可以看到图像的轮廓。之后，便携式暗箱诞生，内置镜子和制图板让艺术家可以捕捉到图像。对于艺术家来说，这项技术使得景物的外表和线性透视能够被精准地描绘出来，因为艺术家可以从单一的视角来观察它们。镜子的使用也使得倒立的投影变为正常。

那么在当时，是否有绘画大师曾使用暗箱来描绘图像呢？一些艺术史学家正在寻找相关线索，证明确有此事。用这种角度对其画作进行分析的艺术家之一是杰出的荷兰画家杨•维梅尔（1632-1675）。在他生活的这段时期，荷兰的艺术和科学（包括光学）正值繁荣兴盛。维梅尔知名的画品只有30幅左右，这其中包括他的著名作品《绘画艺术》。画中描绘的房间与维梅尔的其他画作中的房间极为相似：光线都是从左边窗户照入，一样的横梁，相似的地板砖，这些都表明房内前侧方位置可能装有一个暗箱。挂在对面墙上的地图是维梅尔现实中拥有的物品，地图的细节还原得如此真实，不得不让人质疑是否出于描摹。当用X射线检测这幅画时，颜料下的帆布上并没有任何草图的痕迹，有的只是一副干净完整的黑白画。维梅尔没有学生，没有留下任何记录，也没有邀请任何人去参观他的画室，人们解释说这是因为他在秘密地使用暗箱。

近些年来，英国艺术家大卫•霍克尼发表了他对画家秘密使用暗箱的调查结果，声称在长达400年当中，许多西方艺术大师有可能借助了这一设备来描摹他们画作当中格外逼真的部分。这些大师包括卡拉瓦乔、汉斯•荷尔拜因、列奥纳多•达•芬奇、迪亚哥•委拉斯开兹、让•奥古斯特•多米尼克•安格尔、阿尼奥洛•布伦齐诺、以及扬•凡•艾克。从艺术家的角度来看，霍克尼观察到暗箱可以将复杂的三维场景变成易于捕捉的二维图像，并增加光与影之间的反差，从而产生了在很多这类画中常见的明暗效果。在扬•凡•艾克的画作《阿尔诺芬尼夫妇像》中，枝形吊灯按透视法缩短了，加上画中呈现的新娘服装的复杂细节，这些线索使得霍克尼认为作者使用了暗箱。

综上，我们要得出什么结论呢？如果这些艺术家的确用了暗箱，这会不会降低他们的声望？霍克尼认为，暗箱不能取代绘画中的艺术技巧。通过亲身实验，他发现暗箱其实很难用于绘画。于是他推测，艺术家在借助暗箱捕捉图像作画时，很可能也结合了他们生活中对原物的观察结果。