Carl Zeiss NfPk

is a research microscope from the "Tripod N" series. It is a further development of the well-known L microscopes with the application areas Lp and Lu in one device. It was primarily designed for work with transmitted light, but with different methods.

The microscope was produced in various modifications for the aforementioned transmitted light or reflected light. In addition, there were different configurations of working tables, where:

Table B had a round, centred, rotatable table

table Bt was based on the round version B andallowed 360° rotation, had an angular scale, centering, position locking and the attachment of a guide element

table H was similar to variant Bt, but in addition to rotation, centring and locking, the top could be manually moved laterally at will within a range of 25 × 25 mm

table C was square in shape and fixed to the tripod, its top was made of hard rubber and thus designed for working with corrosive substances

table K was also square, but with a built-in cross-axial movement with the possibility of rotation; the range of movement of 76 mm × 50 mm could be read to within 0,1 mm of the marked scale

The pancratic triple condenser optics system is a specific optical unit with a precision designed optical assembly with variable numerical aperture. The three-lens assembly includes a large-field condenser for low numerical aperture lenses, a 1.4 aplanatic condenser for apertures from 0.16 to 1.40, and a 1.05 cardioid condenser for dark-field illumination. The entire system is capable of varying the correct luminous flux to achieve precise Köhler illumination.

A dedicated phase condenser is not required when using the pancratic system on an Nf tripod. Instead, a phase ring and aperture attachment is clamped to the pancratic condenser from below to the centering bracket, The correct size of the aperture ring images in the rear focal plane of the lens can be achieved by rotating the pancratic system and checked with the phase telescope supplied in the kit.

The NfPk also included a micrometer eyepiece, which allowed precise measurement of the observed objects.

The actual microscope was originally used for observation and microscopic photography in phase contrast, but this method has been replaced by the Carl Zeiss PERAVAL Interphako microscope. To make the NfPk usable, it has been modified to use fluorescence with a 365nm LED source, a 400nm excitation and a 420nm emission filter. Because of this method, orange shields were placed on the trinocular head and to the condenser to prevent damage to vision.