—To better understand the performance capabilities of the E-Series lenses, it’s essential to highlight the concept of the diffraction limit. Central to this is the Airy disk, which represents the smallest point to which a beam of light can be focused through an imaging lens. The size of the Airy disk is dependent on the lens’s f/# as well as the wavelength of light used. The Airy disk is the diffraction pattern produced when light passes through a circular aperture, such as that found in an imaging lens. The radius of the central bright spot of this pattern, known as the Airy disk, partly determines the diffraction limit of the lens. This limit is the theoretical maximum resolving power of the lens, expressed in line pairs per millimetre (lp/mm), beyond which two Airy patterns are no longer distinguishable. While the diffraction limit sets the upper-performance boundary of a lens, real-world factors such as lens design limitations and manufacturing imperfections can further reduce the lens’s ability to produce the smallest achievable spot, thereby affecting resolution and contrast.
E-Series Performance
The E-Series is comfortably able to resolve upwards of 180lp/mm (at >20% contrast), equivalent to the Nyquist frequency of a 2.74um pixel size camera such as the 8.1MP 2/3″ (IMX546, 4th Gen Pregius S sensor) with both monochromatic (blue, green, red) and polychromatic white light due to these lens’s excellent colour correction. The 35mm E-Series lens serves as a prime example of this product line’s capabilities. Analyzing the Modulation Transfer Function (MTF) curve (polychromatic VIS), we observe that the performance across the image plane (coloured lines) closely approaches the diffraction limit (black line). MTF curves are invaluable tools for assessing lens performance and determining the optimal lens-sensor pairing. The E-Series lenses also deliver good performance across the visible (VIS) to near-infrared (NIR) spectrum. They are suitable for both monochromatic as well as polychromatic VIS-NIR applications without the need for focus adjustments (albeit at slightly lower resolutions: compatible with 3-5MP cameras depending on the chosen waveband). Measuring approximately 25mm in diameter and 30mm in length, the lenses are extremely compact for C-mount lenses. They feature a variable aperture for flexibility and an M12 lens style threaded focus adjustment, similar to Edmund Optics‘ Ci series, which saves on size and cost. These lenses can operate between 250mm and infinity working distance but are optimized for 1-3 meters, aligning with many logistics applications.
Semi-Customization Options
The E-Series lenses have been designed to maximize performance at slower f/#s (f/4-f/16, optimized for f/5.6). This approach simplifies the design, lowering overall costs, while also providing greater depth of field. This increased depth of field reduces the need for refocusing when inspecting objects at various distances, making them ideal for logistics, barcode scanning, pattern detection, and robotics vision applications. To enhance their versatility, E-Series lenses offer easy semi-customization, including:
- Ruggedization: To withstand harsh environments prone to shock and vibration.
- Waterproofing: Suitable for outdoor or high humidity conditions.
- Fixed Aperture: Replacing the iris with a fixed aperture to further reduce costs.
- Liquid Lens Integration: Integrating a liquid lens for applications requiring rapid refocusing across extreme working distance ranges.
Conclusion
Edmund Optics‘ E-Series lenses provide a compact, high-performance solution at a cost-effective price, ideal for cost-sensitive applications. They offer near diffraction-limited image quality and flexible customization options, making them a perfect blend of affordability, performance, and versatility. Additional focal lengths are in development to complement the existing 16, 25, and 35mm lenses, further expanding the series product line.