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Lot Essay
Another three-colour camera associated with George Wells was sold in Cameras and Optical Toys, 6 March 1997, lot 292.
George Wells compiled the following notes about this camera:
The Wells prototype beam splitting colour camera - 1945
Experience had shown that separation negatives exposed through 'standard tricolour' filters were capable of giving good quality colour prints by several printing processes - notably Trichrome Carbro. The conventional method of obtaining the negatives by sequential exposures placed considerable restrictions on the type of subject.
Although experiments with the so-called repeating back which speeded the change of filter and plate enabled the three exposures to be made quite quickly this did not allow instantaneous exposures or the use of flsh bulbs.
The obvious solution was the beam splitting camera and there were several produced commercially. Those which used partly reflecting mirrors divided the lens beam to the three focal planes fitted with the tricolour filters and were capable of giving good quality negatives using commercially available plates. The restrictions in using these cameras were:
1. The space needed for the two mirrors necessitated a long focal length lens
2. The cameras were bulky and difficult to hand hold
3. The overall speed was very low and this was further reduced if correction filters were needed to compensate for the sensitivity of the available plates. Such filters were preferred to changing the mirrors.
Planning
In planning the design of the Wells colour camera to overcome or ease these problems a major decision was made. Instead of using the 6 x 9cm. or quarter-plates in general practice the camera would by 'miniaturised' to use 4.5 x 6cm. plates. This reduced the bulk and more importantly the focal length of the lens and thus the depth of field available at wide aperture - in effcet doubling the speed. With coupled rangefinding the cameta could be hand-held.
Construction
The body of the camera is fabricated from sheet brass and although this was possibly not as accurate as a machined casting, the method of mounting the two mirrors allowed for correcting any errors. There are two tunnels connected to the plate holder positions. At the end of the tunnels are three screws against which the mirror planes are held. These screws were adjusted to compensate for any register errors. To change a mirror the tunnel is withdrawn from the body and the replacement mirror is attached against the three screws without affecting the register.
For the purpose of the prototype the lens and optically coupled range finder were 'borrowed' from a Super Ikonta.
Conclusion
By careful choice of reflection/transmission of the mirrors a 'camera speed' of the equivalent of about 12 ASA was achieved. Further experiments were tried with different mirrors to increase speed. The standard metal deposit on the mirrors was aluminium and the use of gold helped a little by increasing the red reflection and the green transmission.
The arrival on the market of the new transparency films, notably Kodak Ektachrome, from which separation negatives could be made using suitable masking techniques meant the demise of the beam splitting cameras.
George Wells compiled the following notes about this camera:
The Wells prototype beam splitting colour camera - 1945
Experience had shown that separation negatives exposed through 'standard tricolour' filters were capable of giving good quality colour prints by several printing processes - notably Trichrome Carbro. The conventional method of obtaining the negatives by sequential exposures placed considerable restrictions on the type of subject.
Although experiments with the so-called repeating back which speeded the change of filter and plate enabled the three exposures to be made quite quickly this did not allow instantaneous exposures or the use of flsh bulbs.
The obvious solution was the beam splitting camera and there were several produced commercially. Those which used partly reflecting mirrors divided the lens beam to the three focal planes fitted with the tricolour filters and were capable of giving good quality negatives using commercially available plates. The restrictions in using these cameras were:
1. The space needed for the two mirrors necessitated a long focal length lens
2. The cameras were bulky and difficult to hand hold
3. The overall speed was very low and this was further reduced if correction filters were needed to compensate for the sensitivity of the available plates. Such filters were preferred to changing the mirrors.
Planning
In planning the design of the Wells colour camera to overcome or ease these problems a major decision was made. Instead of using the 6 x 9cm. or quarter-plates in general practice the camera would by 'miniaturised' to use 4.5 x 6cm. plates. This reduced the bulk and more importantly the focal length of the lens and thus the depth of field available at wide aperture - in effcet doubling the speed. With coupled rangefinding the cameta could be hand-held.
Construction
The body of the camera is fabricated from sheet brass and although this was possibly not as accurate as a machined casting, the method of mounting the two mirrors allowed for correcting any errors. There are two tunnels connected to the plate holder positions. At the end of the tunnels are three screws against which the mirror planes are held. These screws were adjusted to compensate for any register errors. To change a mirror the tunnel is withdrawn from the body and the replacement mirror is attached against the three screws without affecting the register.
For the purpose of the prototype the lens and optically coupled range finder were 'borrowed' from a Super Ikonta.
Conclusion
By careful choice of reflection/transmission of the mirrors a 'camera speed' of the equivalent of about 12 ASA was achieved. Further experiments were tried with different mirrors to increase speed. The standard metal deposit on the mirrors was aluminium and the use of gold helped a little by increasing the red reflection and the green transmission.
The arrival on the market of the new transparency films, notably Kodak Ektachrome, from which separation negatives could be made using suitable masking techniques meant the demise of the beam splitting cameras.