While it would be possible to have a microscope with a single objective, this is not especially convenient.
The Labophot series does not have removable turrets, which limits the possiblities. Some are forward facing, as shown, and some are rear facing, as is shown for the Eclipse E200. The more capable Eclipse series has removable turrets, but not the E200. The Labophot series uses rms thread (20.32 mm), whereas the infinity corrected Eclipse uses M25 (25 mm) threads.
The Optiphot and Diaphot TMD have removable turrets, which allow features such as DIC prisms for reflected light and BD Plan objectives to be used. They attach via a circular dovetail with a setscrew in the microscope body to affix it. A groove in the bottom registers them. You may notice the center is unused. Motorized turrets have a central protrusion which houses the motor.
Shown here is a simple rms 5 position turret, both empty and with phase contrast objectives installed.
Reflected light (epi-)DIC uses the 210 mm tube length objectives for episcopic systems. Appropriate hardware added to a Diaphot should allow these to be used, but typically they are found on Optiphot systems.
These turrets are incompatible with transmitted light DIC, even though they will attach to the microscope. The problem is that the Nomarski/Wollaston prisms are oriented at 45°, but the DIC condensers have their prisms at 0° (left-right as viewed from the front), which is a serious disconnect for making transmitted light DIC work. In that situation, a single long slider is installed behind the objectives, so a normal turret is used there.
Epi-DIC for the E600, and perhaps others, can be accomplished with the M27 threaded BD turret shown below. Viewed from the back, it is clear that they are BD style, with a central region and an outer annulus separated physically. As seen in the first photo, at the top of the page, this turret is quite a bit larger than the rms version (or 4-position M26 BD) for the finite objectives.
And finally, a 4-position finite BD system with M26 threads and objectives installed is shown.
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