Working Distance | Working Distance
Key Words: N.A., micromanipulators, magnification, oil-immersion objective, water-dipping objective, water immersion objective
Definition:The working distance defines the maximum distance at which a microscope objective is able to focus and is measured from the coverslip/specimen interface in case of an coverslip corrected objective or measured from the front surface of the objective in other types
The working distance (W.D.) of an objective is engraved on the barrel of the objective together with other specifications. In general, the working distance gets smaller as the N.A. of objectives increase. The working distance also gets smaller with increasing magnification power of the objective.
Objectives intended to view specimens in air should have working distances that are as long as possible - as long as N.A. requirements are satisfied.
The imaging of brain slices and live cell imaging has placed great demands on optical systems in terms of long working distances and has resulted in the introduction of water-immersion and water dipping lenses. The N.A. of water dipping lenses is slightly lower than water immersion lenses (e.g. Nikon's Plan Fluor 100x, N.A 1.1 compared to Plan Fluor 100x, N.A. 1.3) but the working distance is much longer -“ up to 2.5 mm. The combination of water dipping and long working distance enables micromanipulation at high magnifications.
Nikon's CFI60 infinity optical system provides objectives that are readily interchangeable on Nikon microscopes allowing the most appropriate objectives to be selected for each application. This optical system also enables both longer working distances and higher N.A.s. Some microscopes (for example, Nikon's Eclipse E200), also incorporate a restriction on the upper limit of the stage movement so that the objective does not make contact with the slide when focusing at short working distances. The choice of working distance specification will depend on the application. In most cases, Nikon objectives have the longest working distances on the market (working distance must always be considered in combination with NA).
Nikon's FN1 electrophysiology workstation is a special purpose upright microscope providing maximum open space for working around a specimen. Dedicated FN1 IR-DIC objectives are 17% slimmer than previous objectives, which provides easier access for micromanipulators and more specimen coverage in small chambers and Petri dishes. The objectives have longer W.D. of 2.5 to 3.5mm, including 3.0mm at 60x and 2.5mm at 100x.
Properties of microscope objectives: [microscopu]
CFI60 objectives: [microscopy.fsu.edu]