What are infinity-corrected objectives?

If you’ve been exploring microscopes or objective lenses, you’ve probably encountered terms like infinity-corrected objectives or infinity optical system, especially with high-end models.

While the name might sound technical, it refers to a specific optical design that offers significant advantages for advanced microscopy.

Let’s break it down and see if it’s something you need.

Finite vs infinity systems

The term ‘infinity’ in this context refers to light rays being parallel, as if coming from an infinitely distant light source.

Finite systems: Older microscopes use finite optics, which involved non-parallel light rays focused at a fixed, standardised distance.

The only problem was that adding any optical components into the system, such as a polarizer or filter, introduced aberrations. Compensating for aberrations only introduced other issues – darker images, ghost images and increased magnification.

Infinity systems: Modern infinity-corrected microscopes solve this issue by introducing a tube lens inside the microscope body.

This lens works with specially designed infinity objectives to create a section of parallel light rays called the infinity space. In this space, you can insert optical components without degrading image quality or altering magnification.

Advantages

• Flexible component integration – you can add multiple elements like polarizers, beamsplitters or prisms into the infinity space without affecting image quality or magnification.
• Consistent magnification – the magnification doesn’t change when switching components, allowing for easy comparison of samples using different contrast methods.
• Hybrid imaging – combine multiple microscopy techniques for richer detail –for instance, overlaying fluorescence and DIC in the same sample.
• Parfocality – focus remains consistent even when switching objectives or adding components, saving time and effort during observations.

Limitations

• Cost – infinity-corrected microscopes and objectives are expensive, making them less accessible for hobbyists or casual users.
• Compatibility requirements – infinity objectives only work with microscopes that have a tube lens. You can’t simply attach them to older finite systems without degrading performance.
• Brand lock-in – many manufacturers design their infinity systems to be brand-specific, limiting your ability to mix and match components.
• Component limits – while you can add optical elements in the infinity space, too many can darken the image or reduce the field of view.

Do you need infinity-corrected optics?

For most casual users or hobbyists, traditional finite microscopes are more than sufficient and far more affordable. They deliver excellent image quality for general purposes without the steep price tag of infinity systems.

However, if you’re working in research or industry – especially if your work involves combining multiple optical components or techniques, such as fluorescence microscopy – an infinity-corrected system is worth considering. The precision and image quality are all but essential for high-level applications.

In short:

• If you’re on a budget or need a simple setup, stick with finite optics.
• If you require advanced capabilities and can justify the cost, you can’t go wrong with infinity optics.