linguistic:paraphrasing
Equipment

Photographic plates, which had the light-sensitive emulsion coated on a thin sheet of glass, were normally used instead of flexible film, both because a general transition from glass plates to plastic film was still in progress and because glass provided the best dimensional stability for three images intended to match up perfectly when they were later combined.

An ordinary camera could be used to take the three pictures, by reloading it and changing filters between exposures, but pioneering color photographers usually built or bought special cameras that made the procedure less awkward and time-consuming. One of the two main types used beam splitters to produce three separate images in the camera, making all three exposures at the same time and from the same viewpoint. Although a camera of this type was ideal in theory, such cameras were optically complicated and delicate, and liable to get out of adjustment. Some designs were also subject to optical phenomena that could cause noticeably uneven color or other defects in the results. The other, more robust type was an essentially ordinary camera with a special sliding holder for the plates and filters that allowed each in turn to be efficiently shifted into position for exposure—an operation sometimes partly or even entirely automated with a pneumatic mechanism or spring-powered motor.

When the three color-filtered photographs were not taken at the same time, anything in the scene that did not hold steady during the entire operation would exhibit colored "fringes" around its edges in the resulting color image. If it moved continuously across the scene, three separate strongly-colored "ghost" images could result. Such color artifacts are plainly visible in ordinary color composites of many of Prokudin-Gorsky's photographs, but special digital image processing software was used to artificially remove them, whenever possible, from the composites of all 1,902 of the images commissioned by the Library of Congress in 2004. The altered versions have proliferated online and older or third-party versions showing these tell-tale peculiarities are increasingly scarce.

Adolf Miethe designed a high-quality, sequential-exposure color camera, which was manufactured by Bermpohl and became available commercially in 1903. Prokudin-Gorsky published an illustration of it in Fotograf-Liubitel in 1906. The most common model used a single oblong plate 9 cm wide by 24 cm high, the same format as Prokudin-Gorsky's surviving negatives, and it photographed the images in unconventional blue-green-red sequence, which is also a characteristic of Prokudin-Gorsky's negatives if the usual upside-down image in a camera and gravity-compliant downward shiftings of his plates are assumed. An inventor as well as a photographer, Prokudin-Gorsky patented an optical system for cameras of the simultaneous-exposure type, and it is often claimed or implied that he invented, or at least built, the camera used for his Russian Empire project. No definite written or photographic documentation of his field equipment is known to exist, only the evidence inherent in the photographs themselves, and no rationale has been suggested for going to the trouble and expense of building a functionally identical copy of a Miethe-Bermpohl camera instead of simply buying one.

Miethe and Bermpohl also produced a matching three-color projector and a chromoscope. The Goerz optical company made a differently configured and more powerful three-color projector for Miethe. It, too, was commercially available.