|
|
| cameras | accessories | gallery | resellers | reviews | workshops | contact | ||||||||
|
LENS COMPATIBILITY
Ebony are frequently asked about which lenses are compatible with which Ebony cameras. The range of usable lenses mentioned in the specifications table for each camera gives a rough idea of whether a particular lens will focus at infinity with a particular camera. For more detailed information however, please consult the following tables of large-format lenses. The tables cover lenses made by the four main manufacturers, and are for reference only. Many of the lenses are no longer in production. Ebony accept no responsibility for any errors or omissions. There are two factors to consider when choosing lenses for cameras, or cameras for lenses. The first involves the image circle of the lens: the lens must produce an image of sufficient size and quality to cover a given format. The second issue concerns focus, and involves the flange focal distance (also known as 'flangeback') of the lens. If the flange focal distance of a certain lens is too long or too short, it will not be possible to focus the lens at infinity with certain cameras. 1) Image Circle The image circle is the circular area of light produced by a lens when focused at infinity at f22. The size of this illuminated area increases as the distance between lens and subject decreases, so that, in general, if the diameter of the image circle produced by the lens is greater than the diagonal length of the film, the lens may used with this film format. There are several provisos to consider however. First of all, as the aperture increases, the image circle shrinks. Thus while a lens may cover a certain format at infinity and f22, it may not cover this format at larger apertures. Secondly, one of the main features of a view camera is the ability to move the lens, and hence the image circle, relative to the film. Obviously if the image circle of a given lens just barely covers a given format, even a small amount of movement may mean that the film is no longer completely covered by the image circle - the phenomenon known as vignetting. In general, the shorter (wider) the lens, the smaller the image circle, and the greater the possibility that using movements will cause vignetting.This is less of a problem with modern lenses which produce large image circles and thus allow a generous amount of movements. Thirdly, with many lenses, again particularly the older designs, image quality and brightness deteriorate to a certain extent towards the edge of the image circle. Thus while the film may still be covered by the outer edge of an image circle, the quality of the image may not be acceptable. The 'Largest formats' column is therefore a rough guide only, and is partly subjective: for example, some might think that a certain lens covers 5x7" with acceptable image quality, while others would disagree and say that it only provides acceptable quality over 4x5". In general the "largest format" column below is conservative - it may be possible to use a larger format with a certain lens in some situations. Also, although several lenses with longer focal lengths may be used with formats larger than 8x10", only the following commonly-used formats are mentioned: 6x9cm, 6x12cm, 4x5", 5x7" and 8x10". 2) Flange focal distance The second factor involves the flange focal distance (or 'flangeback') of the lens, and the minimum and maximum bellows extension (also known as flangeback) of the camera in question. The flange focal distance of a lens is the distance from the rear surface of the lens shutter (i.e. the front surface of the lensboard) to the focal plane (i.e. the film plane) when the lens is focused at infinity. The 'flangeback' of a camera measures the same distance, but in the case of the camera it is variable, in order to accommodate lenses with different flange focal distances. The flange focal distance of the lens must fall between the minimum and maximum bellows extension of the camera for it to be able to focus at infinity. Knowing the flange focal distance of a lens will enable you to determine whether it is possible to focus a particular lens at infinity with a particular camera. With standard lenses, the flange focal distance is usually slightly less than its focal length. However this relationship does not hold for wide-angle or telephoto lenses - the flange focal distance is somewhat greater than the focal length in the case of wide-angle lenses, but very much less in the case of telephoto lenses. Thus, while knowing the focal length of a lens gives you a rough idea of which cameras might be suitable, if you want to be absolutely certain of being able to focus a particular lens at infinity with a particular camera you have to know the flange focal distance of the lens. In the case of a lens with a short flange focal distance, you will needto know the camera's minimum belllows extension, and in the case of a lens with a long flange focal distance, you will need to know the camera's maximum bellows extension. For example, the Ebony 45S has a maximum bellows extension of 270mm. Nevertheless, it will allow a 400mm telephoto lens to focus at infinity, because the flange focal distance of this lens is only 252mm. On the other hand, the SW45 has a minimum extension of 46mm. Nevertheless, it is possible to focus a 38mm super-wide-angle lens because its flange focal distance is 52mm. Although it is easy to determine whether a lens may be focused at infinity with a certain camera, determining how close it will focus is another matter. Closer focusing is achieved by extending the camera bellows. With short to normal lenses for a given format it may be safely assumed that a lens may be used for close-ups. However longer lenses require a large amount of extension for close-ups. The procedure for determining the closest distance at which a long lens may be focused at the maximum extension of a certain camera is too complex to describe here - if you have a question about a specific combination please contact us directly. A final factor to consider is the use of modified lensboards or camera backs to alter the minimum or maximum extension of the camera. To continue with the example of the 45S, with its maximum bellows extension of 270mm it does not allow a 500mm lens with flange focal distance of 350mm to focus at infinity. However with an Ebony 452 extension back, the maximum extension of the camera is increased by 90mm to 360mm, which is now long enough for this particular lens to focus at infinity. Again, the 45S does not normally allow a 300mm compact lens with a flange focal distance of 282mm to focus at infinity. However, if this lens is mounted on a 35mm extension tube (a lens board with a 35mm front extension), the camera's maximum extension is increased to 305mm and it is now possible to focus the lens at infinity. Lastly, the minimum bellows extension of the 45S is 60mm. With a flat board it is not possible to focus a 45mm lens with 55.5mm flange focal distance. However with a 10mm recessed lensboard, the camera's minimum extension is reduced to 50mm, and it is now possible to focus the lens.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| cameras | accessories | gallery | resellers | reviews | workshops | contact | ||||||||