The Nikon LU Plan Fluor 5x is common on the used market even though it’s not currently listed by Nikon being replaced by the current TU Plan Fluor EPI
P 5x. The image quality is pretty consistent over the image field and the chromatic correction is better than an achromat.
This is the Plan Fluor and BD Plan Fluor. One of the biggest differences you can see besides the barrel size is the working distance, 18 vs 23.5mm.
Nikon Part number: MUE41050
Official name: Nikon CFI LU Plan Fluor BD 5X/0.15 ∞/0 Microscope Objective
Objective type: Industrial microscopy
NA and Nominal Aperture: This lens has a numerical aperture or NA of 0.15. this is a nominal aperture is f/2.7 and an effective aperture of f/16.6
Focal length: 40mm
Working Distance: BD objective is 18mm, non-BD is 23.5mm.
Mount: M32 x 0.75 mount for the BD. M25 x 0.75 for the normal Plan Fluor.
Parfocal length: 60mm
Chromatic Correction:
Tube lens length: 200mm. An infinity-corrected optical system consists of two parts – the objective and the tube lens system.
Chrome Free Infinity (CFI): The CFI160 optical system means that the aberrations are corrected within the objectives so there is no need for correction in a tube lens or eyepiece.
Country of origin: Japan
OFN: 25mm
Image circle coverage: The Nikon CFI LU Plan Fluor BD 5X will cover an APS-C sensor with a 26-28mm diagonal except for the extreme corners.
PRICE AND AVAILABILITY
These objectives are pretty common on Ebay in both BD and the normal type so the prices are pretty low. I paid about $300 for this objective in 2018.
WHAT YOU NEED TO KNOW
What I like about the lens
Good sharpness
Chromatic aberration correction
Flat field
Things I don't need
Short 18mm working distance of the BD version
HOW TO SET UP THE NIKON LU PLAN FLUOR 5X BD
The BD or Bright or Dark field lighting channel in the lens barrel needs to be blocked for photography. This is really easy to block with flocking tape, a flocking sheet or with an adapter as I did here. The RafCamera M32 x M25 adapter blocks the BD light path and converts the mounting threads to the more common M25 threads. You can find the adapter here on the RafCamera site:
https://www.rafcamera.com/adapter-m32x075-m25x075-black
LINKS FOR MORE INFO:
Edmunds Optics: https://www.edmundoptics.com/microscopy/infinity-corrected-objectives/Mitutoyo-Infinity-Corrected-Long-Working-Distance-Objectives/
Mitutoyo Objective catalog: http://www.mitutoyo.co.jp/eng/support/service/catalog/04/E14020.pdf
Mitutoyo microscope catalog: http://www.mitutoyo.com/wp-content/uploads/2016/09/I-section-Microscopes.pdf
MICROSCOPE OBJECTIVE SPECIFICATIONS
Identification of the properties of an objectives is easy because most parameters are inscribed or printed on the outer housing (or barrel) of the objective.
LU: Luminous Universal
Plan: Flat Field correction
BD: Bright or Dark Field
Fluor: Fluorite aberration correction