Chris's camera pages
Retina ground glass focusing adapter
Here is a copy of the original instructions for this very unusual accessory.
The KODAK Ground Glass Focusing
Adapter for the RETINA IIc and IIIc is a very useful accessory for all subjects where
the precise field of view and visual estimation of perspective, illumination,
and depth of field are important. Two versions are available, for RETINA Xenon
C and for RETINA Heligon C lens systems. The bayonet mount of the ground glass
adaptor accordingly carries an engraved X (for Xenon) or H (for Heligon).
The ground glass focusing adapter will take the standard lens by itself or with supplementary N- and R-lenses (in any combination),as well as the telephoto and wide-angle lenses. The ground glass screen always shows the exact effect.
Focusing the Eyepiece
Before working with the ground glass adapter it must be accurately set for the standard, wide-angle, and telephoto lenses of the RETINA. First of all, however, the eyepiece (15) requires adjusting to the eye of the user. For that purpose fully open the lens diaphragm, and point the ground glass adapter at a bright surface (a light wall, or the sky). Slack off the eyepiece clamping screw (13), and adjust the tube (14) until the grain of the ground glass screen appears sharp. Then tighten the clamping screw again.
Focusing the Standard lens on
The ground glass adapter incorporates a permanently built-in lens component which forms a complete lens system only with the interchangeable component of the standard lens on the camera. Accurate initial setting is therefore essential. Remove the interchangeable component of the standard lens from the camera and mount it on the ground glass adapter by placing it in position with the red dots in line and turning clockwise as for as it will go.
Set the focusing scale for the standard lens to infinity, and slack off the small screw (11) with a fine screw driver. Turn the ground glass screen by means of the milled screw ring (12) to obtain maximum sharpness at infinity. To do that sight a distant object (e.g. a factory chimney, telegraph pole, etc.) which should if possible be at least 300 feet away. When this distant object appears really sharp, tighten the small screw again, thus locking the screw ring in position. The ground glass focusing adapter is now set for sharp focus with the standard lens. This adjustment must be very exact, as the perfect working of the ground glass adapter depends on it.
Focusing the Tele and Wide-angle
After fitting the tele or wide-angle lens unit, again sight a distant object more than 300 feet away, and focus it sharply by moving the focusing lever (5). If the focusing index does not point to infinity on the corresponding focusing scale, slack off the two small screws holding the pointer for the tele or wide-angle focusing scale respectively, and adjust the position until the telephoto index pointer (6) points to infinity on the telephoto focusing scale (7), and the wide-angle index pointer (9) to infinity on the wide-angle focusing scale (8). These adjustments also need great care.
Setting Up the Ground Glass Adapter
Screw the ground glass adapter to the camera platform, and mount the latter on a table stand or tripod, according to the requirements of the subject. Then fit the lens to be used.
Working with the Ground Glass
To use the ground glass adapter, first settle the field of view, viewpoint, and lighting of the subject on the screen. Once that is done
and the position of the ground glass adapter (i.e. the camera position to be used) is fixed, determine the distance and depth of field.
To do this observe the subject through the eyepiece, or with the eyepiece removed, directly on the screen while moving the focusing lever (5) and adjusting the aperture lever (2).
After determining the distance and aperture (for the required depth of field) with the ground glass adapter, read off and note down the
settings. Then, and only then, remove the ground glass adapter from the camera platform without shifting the latter. Take the lens out of the adapter and mount it or the camera. Set the camera to the same distance and aperture. BUT be sure to transfer the distance setting to the correct focusing scale; the corresponding scales on camera and adapter are in the same colours. After setting the distance select the shutter speed to be used, and only then (because of the aperture-speed coupling) adjust the aperture on the camera.
Taking the Picture
When all settings are correct, mount the camera on the camera platform in the same way as the ground glass adapter was mounted before. Now make the exposure, preferably with a cable release. The film will record the subject exactly as it appeared on the ground glass screen.