The Mitutoyo FS-60 is built to use infinity objectives, principally of the M Plan Apo series which is often discussed in this forum. This is a relatively big microscope, compared to ordinary stereomicroscopes. Its lines are deceptively simple, and it looks smaller than its real size in the picture below. I believe this model was produced until approximately 2005. The current model is the FS-70, quite similar in construction.
The binocular head uses eyepieces with 30 mm barrels, by standard 10x with a field stop (i.e. the diameter of the field of view) of 25 mm. There is a fixed beam splitter that directs 50% of the light to the eyepieces and 50% straight up the photo tube. The small port at the rear of the photo port (i.e. at the right of the photo port in the picture) is for coaxial illumination.
The image in the eyepieces is erect (i.e., like in a stereomicroscope). I am planning to build a camera adapter for direct projection, which brings the sensor plane very approximately 10 cm above the present photo port.
The fine focus knob performs a travel of 100 µm per turn (1 µm per division of the scale). The total travel of the rack is 57 mm and can be performed with either the fine or coarse knobs. As a whole, this is a "slow" rack, even when operating the coarse knob.
The stand is a single-piece cast, very solid but with feet not designed to absorb vibrations. It must be placed on a damped platform for sensitive use. It is obviously designed for incident illumination only, and requires a moving stage to be mounted on the base (a subject directly placed on the base cannot be focused, and must be lifted above the base by a couple of centimeters).
The rectangular hatch opens to reveal some of the internal optics. There is a mirror to bend the light from the illuminator port and a semi-transparent mirror to direct it downward through the objective. The real goodie is the tube lens, partly visible at the top left through the hatch. It is a zoom lens with a continuously variable magnification between 1x and 2x (operated by turning the zoom knob through a 90° angle). This is in fact one of the main reasons why I decided to use this scope for implementing my (hopefully) "final solution" for infinity objectives in photomacrography.
The nosepiece accepts four objectives. Three of the objective mounts are centerable.
The image quality through the eyepieces is very good with the Mitutoyo M Plan Apo objectives, and even with the Zeiss Luminar 63 mm shown in the first picture (which gives a magnification around 2x-4x, or 20x-40x with the eyepieces). The setup shown above gives an almost uninterrupted range of magnification between 2x and 20x on the sensor. The Mitutoyo lenses are almost perfecty parfocal with each other (a slight fine refocusing is necessary) and through the zoom range. The Luminar is not parfocal with the other objectives (it could become, with extension tubes of the right length) and remains almost parfocal through the zoom range.
More information when I have the time, either here or on my web site at www.savazzi.net.
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