A 6x9 Twin Lens Reflex Camera.

A 6x9 Twin Lens
Reflex Camera

G. Carboni, July 2008
Translated by Sarah Pogue

Figure 1 – Detail of a photograph taken with the camera described in
this article. Portrait of my daughter after her birth, taken several
years ago. Photo obtained from a print by means of a scanner.
(Image clickable. When it opens, click again).

INTRODUCTION
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By now, digital cameras have taken the place of film cameras. What sense does it make to propose a film photographic camera today? For many people, black and white photography is still a very interesting field in photography and there are still many fans of photosensitive emulsion technologies. You must consider that what I am about to propose to you is a camera model that will give you great satisfaction.

In photography, a twin lens reflex camera is a camera that has two lenses. One of these is used for framing and the other to expose the film. Since 1929, the German company Rollei has produced numerous twin lens reflex cameras called "Rolleiflex" which were its war horse for many years. Still today, it is possible to find cameras of this type on the market. They have a square 6x6 cm format. At the printers, this format is often reduced to a rectangular 4.5x6 cm format. In this article we will see how you can obtain, with little expense and relative ease, a twin lens reflex camera with a 6x9 cm format with which you can take high quality pictures.

The construction of this particular twin lens reflex is particularly simple. In fact, you won’t have to build the entire device, instead, you will build a simple viewer to attach to an already built camera. It involves, therefore, mounting a visor onto an accordion or view camera in a manner analogous to Rolleiflex. Figure 4 shows a diagram of this structure. On the frosted glass of the viewer it will be possible to frame and focus perfectly. You can use colour or black and white film, however this camera will give greater satisfaction in black and white. In fact, the image that you see on the frosted glass has tones that are very similar to those that the printed image will have and this will permit you to understand if they are clearly distinct, if the subject is detached from the background etc. This is exactly what you want in black and white photography.

The accordion also contributes to the quality of the photograph, as it avoids those reflections from the walls of the camera that lower the tones in 24x36 mm devices. To achieve the best results, the lenses of the objectives of the folder camera should have an anti-reflection treatment, as is by now the general rule for more recent cameras.


Figure 2 – Photograph taken with the camera described in this article. This frame was obtained and digitalised using a scanner from a print.	Figure 3 – Detail of the previous photo. In the left lens of the sunglasses, the 6x9 twin lens reflex camera is visible.

Unfortunately, I can’t show you a decent photo of this machine as I lost it many years ago, a few months after building it. You will therefore have to content yourselves with some rough drawings and my descriptions. The only image I have of this camera is visible in figure 3, in the reflection in the left lens of the sunglasses.

COSTRUCTION
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Obtain the principal components.
To build this twin lens reflex camera, the first thing that you must do is find a 6x9 accordion camera equipped with a good functioning lens. For example, a Voigtländer or a Zeiss. Photographic cameras of this type are quite easily found in photography shops that deal in used or antique photographic equipment and in exhibitions-markets of photographic equipment.

Not all accordion cameras are suitable to this transformation. Those which have a focusing system where the carriage on which the lens is mounted moves forwards and backwards are suitable. However, devices with a focusing system where the lens has a screw-threaded mount that rotates are NOT suitable, as both lenses would need to rotate in the same way. In the end, this solution would be much more complex to realise mechanically than the first.

To make the viewer, a second lens is needed that has the same focal length as the lens of the accordion camera. Normally, the 6x9 cameras are equipped with a lens with a focal length of 105 mm. The lens for the viewer must have a good opening (diaphragm of at least 3.5), it will always be used fully open and its shutter will never be employed. This lens can also be found where you bought the accordion camera.

Design.
Make a detailed design of the viewer, so that you can determine precisely the dimensions of the various parts, in particular the mirror and the frosted glass.

Assembly of the second lens.
The second lens must be mounted in such a way that it is joint with the first. For this purpose, a plate of brass or better stainless steel 1 mm thick is necessary. On this plate you must make the holes for the two lenses. The distance between the holes must be determined from the design. The lenses are easily mounted on the plate by means of their ring nut. Moving the carriage of the focusing system, both lenses move together, as they are on the same plate.

The viewer box.
The visor contains a mirror mounted at 45° in its interior, in this way the image is reflected onto the frosted glass placed horizontally, in a position that is comfortable for the observer. This box can be made from plywood (for example: walnut). Using plywood you will have the possibility to fix the different parts with thin screws and then to glue them with highly resistant Vinyl glue. In the right and left sides, you must fix a pair of plywood plates to screw in the 4 adjusting screws. In front of the viewer, you must make a hole for the passage of the light that forms the image on the frosted glass. Paint the inside of the viewer black.

Telescopic tubes.
In position 3 of figure 4, two telescopic tubes are indicated whose function is to prevent the entrance of external light into the viewer. One of these tubes must fit into the other, without them scraping against each other. These tubes are made using a lathe and their construction is probably the most demanding part of the project.

Assembling the viewer.
The viewer box must be fixed on the camera body. This can be done using an aluminium plate. Open the accordion camera like you would when preparing to take a photo. On this door, it is possible to fix an aluminium plate (position 9 in figure 4) that will connect the viewer to the camera. If necessary, place some spacers to centre the viewer in the right-left sense. Clearly, you will not be able to close the device anymore.

45° mirror.
Cut the mirror down to the necessary size or order one of the correct size from a glazier. Round off the rough edges to remove any sharp points. This mirror will be simply laid at an angle of 45° to the viewer. It could be glued in place or fixed by some other means. For example, with lateral plywood plates.

Rounding the edges of a plate of glass.
Cut down a plate of glass to the desired size (glass to be worked). Place an open newspaper on a table and on top of this place a piece of glass larger than the first (work surface). Pour a half a teaspoon of abrasive powder of approximately 200 grain sized (medium size) and a little water on top of the work surface. Holding the sheet whose edges need rounding at an angle of 45° above the abrasive, drag an edge along the underlying glass with circular or backwards and forwards movements. Every so often you will need to add a little water. When you have finished rounding the edges, move onto another edge until you have done them all. Wash the glass and the work surface well. Avoid spreading the abrasive powder around. The abrasive can be bought at low cost from marble workers (those that prepare headstones). Be careful that coarser emery grains don’t end up in the containers with the finer abrasive.

Frosted glass.
This piece of glass should be a little larger than 6 x 9 cm to be able to place it on the adjusting screws. Cut it down to size and trim the edges with abrasive powder. At this point, the glass is still transparent and it is necessary to frost it on one face. In order to do this, use abrasive powder of 600 grain size or better 1000 grain (very thin). Prepare a second piece of frosted glass 50 x 100 mm in size, whose use will be described shortly.

Frosting a sheet of glass.
The domestic preparation of frosted glass is important for those who delight in photography or more in general in optics.
Cut a piece of glass down to the desired size (glass to be worked) and round the edges. Change the sheets of newspaper and clean all of the equipment so that none of the larger grains of abrasive powder used to round the edges remain. Wash your hands. Place a clean newspaper on the table and on top of this place the larger sheet of glass used before (work surface). Pour a half a teaspoon of very thin abrasive powder and a little water on the work surface. Now, put the piece of glass to work on top of the abrasive and begin to rub the two sheets of glass together using a backwards and forwards or circular motion, whichever you prefer. The abrasive between the two sheets will cut the two surfaces causing the frosting. After some time you will realise that the abrasive has little grip and that the noise has decreased, this means that you must add some more abrasive, and maybe also some water. Bear in mind that the glass must be frosted on one side only. Every so often, check how the work is progressing. To do this, wash the glass under the tap, dry it and check that the frosting is complete. If there are still some shiny or transparent parts, you must continue the frosting pressing moderately on those areas. At the end, wash the glass well also using soap. All of these activities must be done whilst avoiding spreading the abrasive powder everywhere as this could end up on the lenses and scratch them. To summarise, organise yourselves to round the edges of the three sheets and then frost the two sheets of glass (don’t frost the mirror). The grain of the abrasive determines that of the frosting. With a grain of 600 or better 1000 (very thin), you can obtain excellent frosted glass. To avoid the problem of contamination of the finer abrasive powders with residue of the coarser abrasives, you can carry out the frosting first and the rounding of the edges after. In this article you can see some images on the activities of frosting and edge rounding: http://www.funsci.com/fun3_it/guida/guida6/micro6.htm#2.15 Assembling and regulating the viewer screen.

Mounting and adjusting the screen of the viewer.
The frosted glass that carries out the function of viewer screen is mounted on adjusting screws with the frosted surface facing downwards. The regulation of the height of the frosted glass must be done in such a way that, when the image is in focus on the viewer, it is also in focus on the film. To make this adjustment, a second pane of frosted glass is necessary to place behind the open camera (this is the 50 x 100 mm sheet of glass mentioned previously). The frosted surface of this second sheet of glass must face the lens. Fix the sheet with rubber bands so that it adheres to the scrolling plane of the film. Mount the camera on a tripod and point it at a distant wide panorama. Open the diaphragm to the maximum. Set the lens to "T" (when taking the photo, the lens remains open). With the help of a strong magnifying lens and acting on the focusing system of the camera, focus a distant object on the frosted glass and which is on the same plane as the film. With the adjusting screws, adjust the height of the screen of the viewer until you see the same image in focus. Pointing at a distant panorama, you can also adjust the coplanarity of the screen of the viewer: the image should be in focus both in the centre and at the four corners of the frame. The adjusting screws must be a little tight in their places so that they don’t move after the adjustment is carried out. If necessary, you can also fix them with a little coloured paint.

Thin cardboard cover.
A cover of thin black cardboard opportunely cut and placed under the frosted glass of the viewer will make the framing on the viewer coincide with that on the film.

Shutters.
In position 12 of figure 4, the shutters are indicated which serve to create a dark well in which to better make out the frame without interference from external light. The two shutters on the long sides can be made with thin metal sheets and covered with a black flexible material glued to the sheets, such as thin leather or fake leather. This material can be used to cover the entire external surface of the viewer. Observe in cameras equipped with shutters how such a device is realised.

Lens.
It is not indicated in figure 4. This is a lens to use to precisely adjust the focusing system. This lens can be mounted in a tube of the correct length to be simply leaned on the screen. It should be possible to find lenses mounted on a support that rotates 90° on the market, such as those in the Rolleiflex cameras.

Strap.
Thus transformed, the camera will no longer close. To facilitate its transport when you use it, it is necessary to fit a side strap to prevent the camera hanging with the lens facing downwards.

Analog or digital?
Once you have the negative, you can treat it with analog technology (print it with the enlarger, photosensitive paper, baths etc.) or with digital technology (scanner, software for the elaboration of images etc.). In any case, you can obtain prints of excellent quality. In fact, this camera uses a 6x9 cm film! This means that with the B/W films today available on the market and with the possibility to have a practically perfect focusing system, you can easily obtain photographs in which the weave of clothing fabric, the fine embroidery of a blouse, single eyelashes etc. stand out.

Resolution.
Since colour film has a resolution of 50 lines/mm, and therefore of 100 pixel/mm, the potential resolution of this photographic camera should be 54 Mpx (54 million pixels). This value comes from the product of 60x100x90x100. Commercial B/W films have a resolution at least double that of colour films, therefore, for a 6x9 cm format, you could obtain approximately 200 Mpx. This is a high resolution still today. It will be appropriate to purchase a scanner with the capacity to capture 6x9 cm negatives, with a resolution of at least 4800 dpi (dots per inch). In this way, as soon as you have developed the films, you can transfer the images to a CD or DVD and avoid the usual problems of the films such as the atmospheric damage, the damage due to scarce rinsing of the films. Given that CDs also tend to degrade, our hero should conduct an investigation on the market to find those who sell digital systems for long term storage.

CONCLUSION
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With little expense and a limited amount of work, it is possible to obtain a twin lens reflex camera with a 6x9 cm format. Due to the viewer with which it is equipped, this device allows you to easily evaluate the tonal proportions in the prints. By virtue of the relatively large format of this instrument and the accurate focusing it allow, you can obtain highly detailed shots. Such characteristics make this camera particularly suitable for black and white photography, allowing you to obtain excellent results.

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