This is description of this part:
Olympus LMPlan Apo 250x/0.90 BD ∞/0 microscope objective with W26 / M26 thread - intended for Olympus BX / GX and MX microscopes.
Important: this is not a microscope objective with an RMS thread. The very similar Olympus 250x/0.90 microscope objective with an RMS thread does not carry "BD" in its name and cannot work in darkfield.
Basic technical and optical parameters:
Manufacturer: Olympus (Japan)
Marking on the barrel: Olympus LMPlanApo 250x/0.90 BD ∞/0
Magnification: 250x
Numerical aperture: 0.90
Working distance (WD): 0.80 mm
Objective focal length: 0.72 mm
Parfocal distance: 45 mm
Optical system: infinity corrected, actual tube lens focal length 180 mm
Cover glass: no - works without a cover glass
Mounting thread: W26 x 0.706 mm (1 in. x 0.03 in.), although the designation M26 is in common use
Objective barrel diameter: 32 mm
Objective weight: 170 g
Correction class: plan apochromat (Plan Apochromat)
Observation techniques: brightfield in reflected light EPI and in transmitted light, darkfield (BD) in reflected light EPI, polarized light in reflected light EPI and in transmitted light, Nomarski differential interference contrast in reflected light (requires the appropriate prism)
Field Number: 26.5
Series: LMPlanApo-BD, UIS system
Intended use: Olympus metallurgical, polarizing and inspection microscopes of the BX, GX and MX series, as well as BXFM modules
A note on the thread type: in the BD objectives of the UIS system Olympus uses the W26 thread, that is an inch thread in Whitworth form (W26 x 0.706 mm). Since most users are accustomed to describing microscope objective threads with the Mxx designation, one very often comes across the statement that these objectives have an M26 thread. This designation is formally incorrect, but it functions as a widespread and acceptable shorthand.
This objective can also be used with classic, biological Olympus BX microscopes - it is enough to replace the objective nosepiece in the microscope with the Olympus U-D5BDRE model. It will then work in transmitted light brightfield (DIA) - but still only for specimens without a cover glass.
To generalize - this objective can work in the following microscopes:
- Olympus BX41 / BX51 / BX61 and their "M" variants
- Olympus BXFM
- Olympus GX51 / GX71
- Olympus MX50 / MX51 / MX61
One more thing that can cause confusion when looking for parts: Olympus microscopes are no longer made by Olympus. In April 2022 Olympus spun off the division responsible for microscopes, and a separate company called Evident was created from it, operating independently from the following year. The Olympus name was still used on the products themselves for some time, which is why today you come across both equipment labelled Olympus and the same equipment under the Evident brand. Apart from the name on the housing, nothing has changed in the technical or optical construction of the microscopes. So - this objective fits microscopes sold under both brands, under both Olympus and Evident.
What is this part needed for?
- if you need a high magnification objective, especially for reflected light (EPI) polarization, mineralogy, metallurgy or materials science
