---
PartData:
    Specs:
        Parfocal Length: 45 mm (may also be specified as 195mm conjugate distance)
        Type (conjugate): Finite Conjugate
        Tube length: 160 mm (Designed for DIN standard microscope with 160 mm mechanical tube length)
        Correction: Plan
        Magnification: 20x-100x (40x recommended)
        Thread type: RMS
---
 
# Microscope Objective

As standard the OpenFlexure Microscope uses a finite conjugate, plan corrected, Microscope objective, with 45mm parfocal length. The magnification depends on what you want to look at. We recommend 40x, as with lower magnification the microscope stage may be very slow.

>i To avoid issues, make sure that your objective:
>i 
>i - **Specifies that it is Plan corrected.** Avoid 'Achromatic' or 'semi-plan' lenses as these have poor image quality at the edges
>i - **Specifies a 45mm parfocal length (or 195mm conjugate distance).** Avoid 185mm conjugate distance objectives (some simply use the number 185 in the product description) as these have a 35mm parfocal length and would need a modified optics module.
>i - **Has a magnification of 20x or higher.** Avoid lower magnification objectives as the standard illumination does not fill the field of view of lower magnification objectives. It is possible to defocus the illumination to increase the illuminated area, but this will negatively affect resolution.

See our [information page about how the OpenFlexure optics are designed](../../info_pages/imaging_optics_explanation.md) for further information.
