The Design of the Olympus LB Optics

In a marked departure from previous Olympus microscopes, Olympus designed a totally new family of optics for their flagship family of BH2 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 (see image below).

Other manufacturers of DIN-compliant microscope optics made their own decisions regarding compensation. Nikon for instance 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, significant spherical aberration, and field distortion can result.

Because of the split compensation scheme used by Olympus LB optics, the real intermediate image produced within the BH2 optical tube is unfinished and is therefore not suitable for direct imaging or viewing. This means that the tiny, low-cost eyepiece cameras that drop into the eyepiece tubes should not be used on the BH2, 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.