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Objective Classes

Objectives are categorized into performance classes on the basis of their transmission, chromatic correction, planarity, and others. From the point of view of the International Organization of Standardization (ISO), there are three groups of objective classes differing in quality of chromatic correction.

Objective Class

Field Flatness

Absolute Value(s) of Focus



up to 23 mm

between red and blue wavelength (2 colors) is ≤ 2x depth of field

for standard applications in the visual spectral range


up to 25 mm

for red wavelength and blue to green wavelength (3 colors) are ≤ 2.5x depth of field

for applications in the visual spectral range with higher specifications


up to 25 mm

for red wavelength and blue to green wavelength (3 colors) are ≤ 1x depth of field

for applications with highest specifications in the visual range and beyond

Depth of field: 

Leica Microsystems has aligned all three performance classes of its range of objectives to the needs of its customers and the specific requirements of a wide variety of applications – while offering a convincing price-performance ratio.


HI PLAN objectives feature good chromatic correction at two wavelengths and flatness over the whole field of view. Even the edges of the image are sharp and require no refocusing. HI PLAN objectives are designed for visual fields up to 20 mm. Versions for phase contrast are available. Leica HI PLAN objectives offer good correction properties while being extremely reasonably priced.


The N PLAN objective class comprises further improved achromats with good field flatness up to 22 mm. N PLAN objectives are suitable for transmitted light and DIC, N PLAN PH for phase contrast. For incident light applications including differential interference contrast (DIC), N PLAN EPI objectives are available. The N PLAN EPI BD can also be used as a darkfield objective. The N PLAN EPI incident light objectives feature excellent image contrast and safe working distances.


FL PLAN objectives are modern universal objectives with outstanding chromatic correction and field flatness up to 23 mm.  State-of-the-art coating techniques give FL PLAN objectives high transmission for fluorescence excitation. All contrasting methods are possible. FL PLAN objectives are optimized for fluorescence, PH and DIC.


PL Fluotars are powerful universal objectives with outstanding chromatic correction for at least three wavelengths which makes them suitable for fluorescence imaging.

Field planarity (PL) is computed for a 25 mm field of view. They are made of special glass to enable maximum transmission. This makes them powerful photon collectors in fluorescence microscopy.

Leica’s Fluotar portfolio features various application-optimized correction collars (CORR) to compensate for external influences such as temperature, coverslip thickness and immersion media.


Leica’s PL S-APO objectives come very close to the top-quality objectives of the Leica PL APO class. Magnifications from 1.6x to 63x enable perfect imaging.

Leica PL S-APO objectives are diffraction-limited over the entire visual field.

Their high transmission and chromatic correction make them high-performance objectives for demanding research work.


PL APO objectives – the class for professionals. They deliver imaging quality that cannot be achieved by conventional objectives. Plan Apochromats provide perfect axial and lateral color matching for applications requiring fast color change and the colocalization of structures. PL APO objectives are characterized by flawless image flatness up to a field number of 25. Top numerical apertures define a resolving power at the limits of what is physically possible.

PL IRAPO for Multiphoton Imaging and CARS

Whereas PL APO objectives are corrected in the visible wavelength range, with the PL IRAPO objectives a new set of specialized objectives is now available for improved multiphoton imaging (MP). The IR Apochromats are color corrected from at least 700 nm up to 1300 nm and highly transmissive in the visible and infrared wavelength ranges with > 85 % transmission from 470 – 1200 nm. Thus they are ideal for non-linear imaging like multicolor multiphoton imaging including excitation with OPO (optical parametric oscillator), and CARS (Coherent Anti-Stokes Raman Scattering).

PL APO CS and CS2 for Confocal Scanning

Within the class of apochromats, Leica offers PL APO lenses especially designed to match the highest specifications for confocal scanning (CS). The latest PL APO CS2 series was further improved over the previous CS series. The chromatic correction of the new Leica CS2 objectives is perfect over the whole field of view for precise colocalization of different fluorophores. In addition, numerical aperture and free working distance are pushed to new limits. The design of the Leica CS2 objectives goes hand in hand with the innovative UV optics of the Leica TCS SP8, to give the most stable UV color correction. For aberration-free imaging in aqueous samples such as living cells, Leica Microsystems has developed a series of superior high-resolution water immersion objectives. For the best imaging results, these objectives require a correction collar to adapt the optics to varying coverglass thickness, changing temperature, and specimen inhomogeneity.

Manual adjustment of the correction collar requires time and experience, and is challenging when access to the objective is obstructed by additional equipment. The motorized correction of the Leica motCORRTM objectives simplifies adjustment of the correction collar and reduces training effort. Remote control of the Leica motCORRTM quickly adjusts the optics without disturbing the specimen.

Special objectives

For research involving highly specialized techniques or challenging samples, specially optimized objectives are often needed. Leica Microsystems offers a wide choice of special objectives for such applications.

Some examples:

  • TIRF objectives with top numerical apertures
  • Objectives with high transmission around 350 nm for laser microdissection
  • Special objectives for patch-clamp applications on vital brain sections allowing measurements of individual ion channels using an inert dip-in objective
  • Infrared-optimized multiphoton objectives for the visualization of deep-lying neuronal tissue sections
  • Water, glycerol and multi-immersion objectives with the correct refraction index for the sample medium for aberration-free imaging of thicker samples