Mechanically isolated photomicrography

Normal 'modern' photomicrography without a camera lens or eyepiece is done in monocular microscopes by attaching the camera body to the top of the main tube. In binocular microscopes the entire binocular head can be removed, and a phototube put on. The most prestigeous arrangement is the trinocular head, with an extra image splitter or diverter, and a purpose-built phototube to take the camera.

All these arrangements rely on the microscope being infinitely rigid, and the fine-focus being infinitely stiff. Very expensive microscopes will approach this ideal, but will not reach it. When the objective power reaches 40X, it may be obvious that vibration is destroying sharpness, but much more common is 'focus jump'. You focus accurately, take your picture, and find the plane of focus is not quite where you thought you had set it. Taking ten pictures to get the correct focus by accident is a slow business.

The problem is that the camera is resting on the fine-focus mechanism. More expensive designs may isolate the fine focus, and leave the camera sitting on the coarse focus. A very slight shock to the camera moves the focus setting slightly, and your preset focus is lost.

Almost a hundred years ago, the problem was well-known. Photomicrographers mounted both the microscope and camera rigidly, but stopped them mechanically contacting each other. The decoupled camera can be touched without movement feeding back to the objective focus, and the whole device is in addition much less sensitive to room vibration.

The basic photo-table (left), which was new to me, but has no doubt been invented frequently, has a 22 kilogram disc weight mounted on three rigid legs. All three legs have threaded-nut adjusters, which stand on a thick concrete disc. The centre of the disc weight has a 50mm hole through which the weight-lifting bar originally passed. The Olympus monocular GB40 microscope (about 1970) bas an extended base bolted to it, and this base also rests on three threaded-nut adjusters which contact the same concrete disc. To lift the assembly high enough above the carpeted concrete floor, the concrete disc rests on a cast concrete drainage pit, which could have been filled with pebbles to increase mass, but was quite solid enough without.

An accurate circular bubble-level is placed on the 22 kilogram table top, and the three adjusters altered, then locked when the top of the table is level. The microscope is located so the top tube passes centrally through the hole in the top with space to spare. The eyepiece, and the eyepiece mount, are both removed, and table height is such that the top tube when focused does not stick out above the table top. The plane of focus of a 160mm objective on the microscope is well above the table surface. A short turned cylinder is dropped on the top tube, and the bubble-level placed on that. The three adjusters on the microscope base are now altered until the face of the top tube is accurately level. Since both the table and the top tube face are now levelled, the tube is precisely at right angles to the table. Both the table and the microscope rest on the concrete disc, but they are not in contact with each other. A camera can now be positioned resting on the table, above the central hole, in the right position to receive the focused image from the microscope objective. Because the camera is not in contact with the microscope focus mechanism, the system is completely stable, and no precautions need to be taken during photography. Not even a cable release is required.

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Coming back to the camera. I took off the front face of the metal Ricoh bodyshell, removed the camera lens, and mounted a carefully-dimensioned brass ring inside the front face. I was then able to turn up a much larger brass flange (left) which bolted to the internal ring, and located the front metal face firmly between the two. I could then tap the large brass flange to receive subsequent adaptors. The Ricoh was only a cheap camera, but the metal case had been properly built, so the front face was accurately parallel to the 'film plane'. This made alignment of the brass flange face easy.

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Bolted to the brass flange was this solid aluminium angle, which also made contact with the base of the camera. This added rigidity to the flimsy metal shell. On the front of this angle was fastened an aluminium disc, with four recessed neodynium magnets, and these stuck to the top surface of the photo-table. All joints were recessed for fit, and turned accurately flat.

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The camera/disc assembly shown in the last photo drops (left) with minimal clearance into another aluminium plate with a central hole. This outer plate carries many small recessed magnets, and sticks down hard to the table top. The outer plate is tapped around with a central sighting device fitted until the hole is precisely concentric with the microscope objective. Concentricity can be set to about 0.2mm.

Once the outer plate is located, the camera mounting is set, and no realignment is required for months, unless someone collides with the table.

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This is a Zeiss 12X eyepiece, fitted into a disc of the same diameter as the camera. It can be dropped into the hole in the top plate to replace the camera, and create a conventional microscope. The eyepiece focus has been tuned so it focuses at the same point as the camera. This is very convenient, but not absolutely necessary, as with practice focus using a magnifier on the back LCD screen of the camera is very precise. Focus jump? - no such thing. What you see is what you get.

Today's update

Life has similarities to a banana-skin. You slip up when least expecting it. I had just finished the above, settled down to the week's photomicrography to update the Index, when the six month old Ricoh RR211 camera failed. No imaging - nothing. Nothing works without it. In a few hours I had found my local camera shop still had one in stock, bought it, transferred my modified front panel, and was back taking pictures. The Melbourne branch of Ricoh was also helpful, and I have posted the broken camera body back to them. They may be able to do something.

This underlines just how new digital cameras still are, and how far they still are from reliability. Using them more than twice a year will be costly until the technology matures.