Olympus LB Optics for the BH2 Microscopes
Click the following links to see detailed specifications of the components of the LB optical series.
In a marked departure from previous Olympus microscopes, Olympus designed a totally new family of optics for their flagship family of BH-2 microscopes, which launched in 1980. This new family was called the LB (Long Barrel) optical series, and it included a comprehensive collection of finite-conjugate objectives (both dry and immersion), with a matching suite of eyepieces and photo eyepieces. The various objectives in the LB family were designed to cover a broad range of microscopy types, including brightfield, darkfield, phase contrast (PL, PLL, NH, NM, and relief phase), Nomarski DIC, polarizing, and UV fluorescence.
LB optics were designed to be compliant with the existing German DIN standards of the time. These standards specified the optical tube length (160mm), the parfocal distance of the objectives (45mm) and the mounting threads of the objectives (0.7965″ RMS threads), but did not specify how or where the compensation for optical aberrations should be accomplished. Lacking a specification for this, manufacturers were free to define their own standards. Olympus designed the LB optics with partial correction for optical aberrations within the objective lenses and final correction within the eyepieces and/or photo eyepieces. Other manufacturers of DIN-compliant microscope optics made their own decisions regarding compensation. Nikon designed their CF (Chromatic-aberration Free) series to include all of the necessary compensation within the objective, while other manufacturers chose to split the compensation in a manner similar, but not identical, to what Olympus used. Because of all of this, objectives from one manufacturer are not generally compatible with eyepieces or photo eyepieces from another manufacturer, whether or not they are DIN compliant. While the DIN standard succeeded in ensuring that DIN-compliant optics were compatible across DIN-compliant microscope stands, this was only true to the extent that the entire optical systems were cross-compatible. Individual optical elements are not generally cross-compatible and should therefore not be intermixed with optical components from other manufacturers. To guarantee optimal performance of the optical system, you should always make sure that objectives are used with eyepieces and/or photo eyepieces from the same manufacturer and from the optical family. If this rule is not followed, chromatic aberration, spherical aberration, and field distortion can result.
Because of the split compensation scheme used by Olympus LB optics, the intermediate image produced within the BH-2 optical tube is unfinished and is therefore not suitable for direct imaging or direct viewing. This means that the tiny, low-cost eyepiece cameras that drop into the eyepiece tubes should not be used on the BH-2, nor should direct projection of the intermediate image onto the camera sensor be employed. Additionally, third party adapters and couplers intended to attach a camera to the scope should not be used, unless their design is such that an LB eyepiece or photo eyepiece is present at the appropriate position within the optical path, and that the camera is at the appropriate position relative to the eyepiece or photo eyepiece.
Objective Lenses
Objective lenses in the Olympus LB family were made in several basic optical designs, which determined their overall degree of aberration (spherical and chromatic) compensation. These basic designs were: 1) achromatic, 2) fluorite, and 3) apochromatic. The lowest performing of these three types were the achromats, while the highest performing were the apochromats. The fluorites fell in between achromatic and apochromatic performance (this is why fluorites have often been referred to as “semi-apochromats”).
Separate from the three basic optical design types listed above, LB objectives were made with various degrees of field coverage and flatness. These include a collection of low-cost educational objectives (marked “E” on the barrel), a collection of standard non-plan objectives (referred to as D objectives in Olympus literature, but marked “A” on the barrel), a collection of plan objectives (marked “DPlan” on the barrel), and a collection of super-wide plan objectives (marked “SPlan” on the barrel). The E educational objectives were always achromats of non-plan design with a modest field number of 18. The D (A) objectives were primarily achromats, but some apochromats were also made, and were non-plan with a standard field number of 20. The DPlan objectives were made in both achromats and apochromats, and were fully plan with a standard field number of 20. The SPlan objectives were also both achromats and apochromats, and were fully plan up to a super-wide field number of 26.5.
LB objectives were made to support various optical modes. E educational achromats were made in brightfield versions only. D (A) achromats were made for brightfield, darkfield, phase contrast (PL, PLL, NH, NM, and relief phase) and low-strain polarizing applications. DPlan achromats were made for brightfield, darkfield, and low-strain polarizing applications. SPlan achromats were made for brightfield, Nomarski DIC, and phase contrast (PL, NH, and relief phase) applications. Low-fluorescing D apochromats were made for brightfield, darkfield, Nomarski DIC, phase contrast (PL), and UV fluorescence applications. Low-fluorescing DPlan apochromats were made for brightfield, Nomarski DIC, phase contrast (PL), and UV fluorescence applications. SPlan apochromats were made for brightfield and phase contrast (PL) applications. Low-fluorescence fluorites were made for brightfield, darkfield, phase contrast (PL), and UV fluorescence applications. Additionally, LB objectives were made to provide long working distances (LWD) and ultra-long work distances (ULWD) for inverted microscope applications. LWD and ULWD achromats were made to support phase contrast (PL and relief phase) and Nomarski DIC applications.
LB objectives were commonly available for dry (i.e., non-immersion) imaging, as well as for oil-immersion imaging. The dry objectives were suitable for lower numerical aperture requirements, whereas oil-immersion was required when numerical apertures greater than 0.9 or so were needed. In addition to the common oil-immersion objectives, Olympus also made LB objectives to meet specific industry and research requirements, such as objectives made for water immersion and silicone immersion. LB objectives were also available for viewing without a cover slip. Many of the high numerical aperture SPlan, UVFL, or D Apo objectives, as well as many LWD and ULWD objectives, included a correction collar to accommodate non-standard coverslip thicknesses. Additionally, some of the high numerical aperture A (D), DPlan, UVFL, and D Apo objectives included an internal iris diaphragm to reduce the NA for darkfield imaging.
Eyepieces
Eyepieces in the LB optical family were available in multiple varieties. Standard 23mm diameter versions were made to provide 5x, 8x, 10x, 12.5x, 15x, and 20x magnifications (which were suitable for the various field number 20 objectives), and 30mm diameter versions were made to provide 8x and 10x magnifications (which were suitable for the field number 26.5 objectives). The following eyepiece types were available: 1)CWHK eyepieces (high-eyepoint, field number 18), which were made to pair with the educational E objectives. 2) WK eyepieces (standard eyepoint, field number 20) and WHK eyepieces (high eyepoint, field number 20), which were made to pair with the A and DPlan objectives. 3) NK eyepieces, which were special versions to provide very low (5x, standard eyepoint, field number 21) and very high (20x, low eyepoint, field number 10) magnifications. 4) SWK eyepieces (standard eyepoint, field number 26.5) and SWHK eyepieces (high eyepoint, field number 26.5), which were made to pair with the SPlan objectives. The various 23mm eyepieces were compatible with the standard binocular and trinocular viewing heads, while the 30mm eyepieces were compatible with the super-wide binocular and trinocular heads. Versions of the various eyepieces were avaible with internal optical graticules, for specific measurement applications, and helicoid focusing, for custom graticule use.
Photo Eyepieces
NFK Photo eyepieces (also known as photo projective lenses or photo relay lenses) were made to provide 1.67x, 2.5x, 3.3x, 5.0x, and 6.7x magnifications. These were made to be placed into the NFK receptacle on the camera tube of the trinocular head(s), to intercept the unfinished intermediate image produced by the objective lens and project a fully corrected, finished image onto the film or image sensor plane of an attached camera. The various magnifications were made to accommodate the common film formats of the day.
Phase-Centering Telescopes
The CT-5 and CT-30 phase-centering telescopes were made to allow proper setup of the LB phase contrast optics. The 23mm diameter CT-5 was compatible with the standard binocular and trinocular heads, while the 30mm CT-30 was compatible with the super-wide binocular and trinocular heads.