Preparation of a Ground Glass

Using the integrated camera system II means that one will be correcting for parfocality between the camera and oculars with the shutter assembly optics not the cameras tube length. The process is the same for any of the Bausch & Lomb integrated camera systems and the effect is functionally identical to increasing the cameras tube length. This may not be immediately clear to anyone using the device because on a number of models the adjustment is marked with an “x”. Rest assured that focusing the knob to “15x,” is not going to provide an increase in magnifying power of 15 times over the obdective magnification. Provided this little endeavour is successful, I’ll look into calculating the power of the lens system when in focus. Unfortunately, before any of that a method of obtaining clear focus in the plane of the film will be required. An ideal method of obtaining focus would be inserting a ground glass in place of the film holder. The ground glass would need to be in some type of frame so as to keep the ground surface at the same position the film would occupy. It would at first seen expedient to place a piece of waxed (or oiled) paper onto the camera back and this would work in a pinch. A far better opption would be to cut a sheet of glass to size. If one hasn’t got a sheet of glass to hand a quick trip to the nearest second hand shop or discount store (where a picture frame can be had very economically) will provide the needed material. If one hasn’t got a glass cutter or is not confident in their use of one, a stiff sheet of lexan or transparent acrylic that may be cut with a hand saw will do. If one intends to use glass a finely ground surface may be quickly achieved with a bit of carborundum powder. One must take care to cut the glass to size before grinding. For determining size I have considered two methods. First one may trace out and cut the glass to match the outside dimension, of the plate holder. Alternatively, one may trace the dimensions of a sheet of film and cut to that size. The former is likely the easier option, but if one is careful and has a spare or broken film older the later may prove a more secure and attractive option. In the first case, one will later be supporting the glass with shins to bring it into the film plane. It may be easier in the sense that one may make alterations with little trouble if initial results are not all that one could hope for. Another option would be deconstructing a film holder so that it provides an empty frame into which one may fit the ground glass. Originally sold with a frame supported ground glass, I have never seen a 4×5 body for the Integrated Camera System on the market together with the glass back and feel it likely that most were either broken or lost track of over the years since the apparatus was in active production. It may be worth noting a few points concerning focusing with a ground glass. Focus is limited in sharpness by the fineness to which the glass in question is ground. To obtain an area for perfect focus, one should then cement a cover slip in the center of the ground glass or leave a small area unground. When the clear area is observed using a hand lens or small focusing magnifier one may observe the quality of image that will be captured on film. To leave an area unground one may mask it with a layer of heavy tape (or even a cemented cover slip) which must then be removed after grinding. To grind the glass one need only introduce a little carborundum grit in water to one side of the glass. A second piece of glass (a plain slip works well) is then sanded over the grit under light pressure.

The gallery below demonstrates the process.

Above may be seen my poor abilities in cutting glass, and two ways to go about creating a ground glass for focusing. First a 4×5 piece of glass salvaged from a broken window is inserted into a film holder that had irreparably damaged dark slides. The solid film holders were removed and the glass is supported by the top and bottom of the holder rather than the sides. As an alternative I cut a piece of 1/8th inch acrylic to the size of the film holder. Rather than grind it I simply left in place the frosted protective film on one side. It should be noted that in each case the frosted surface is the one which should be held in the film plane. This means that the in the wooden holder the frosted surface is facing down and in the case of the acrylic it is facing up.