In the field of infrared optics, the intuition that "smaller pixels equal sharper images" has become almost conventional wisdom. However, for continuous zoom lenses—a specialized category—blindly pursuing small pixel pitch may not only drive up system costs but also compromise detection range and imaging performance. This article reveals the often-overlooked trade-offs between pixel size and system optimization.

I. The Misunderstood "Small Pixel"

Over the past decades, infrared detector technology has advanced rapidly, with pixel pitch shrinking from an initial 50μm down to today's 12μm, 10μm, and even 5μm or 1μm in laboratory settings. For fixed-field-of-view lenses, small pixel pitch does deliver significant SWaP-C (Size, Weight, Power, and Cost) improvements—more compact system designs and lighter handling.

However, when this logic is directly applied to continuous zoom lenses, the situation becomes considerably more complex.

The uniqueness of continuous zoom lenses lies in their need to maintain a clear, stable image plane throughout the entire focal length variation. This means the optical system must achieve diffraction-limited performance across the whole zoom range, demanding far greater design margins and manufacturing precision than fixed-focus lenses.

II. The Four Hidden Costs Behind Small Pixel Pitch

1. The Optical Sensitivity Paradox: Small Pixels Could Actually Make Lenses "Bulkier"

Intuitively, the smaller the pixel, the fewer photons each individual pixel receives. To compensate for this loss, the optical system must adopt a faster aperture (smaller F-number)—for example, dropping from F/4 to F/1.2.

But a smaller F-number means:

• Increased optical element aperture: Lens diameters must grow to collect more light.
• Skyrocketing design complexity: Achieving diffraction-limited performance becomes "increasingly difficult and costly" when the F-number falls below F/3.

The net result could be that a continuous zoom system employing small pixel pitch ends up with similar or even larger size and weight compared to a system using larger pixel pitch. This completely defeats the original intention of "small pixels = miniaturization."

2. The Airy Disk and Sampling Theorem: When Pixels Become "Too Small"

According to the Rayleigh criterion, the diameter of the Airy disk for an optical system is approximately 2.44λF. To ensure the detector can effectively resolve two adjacent image points, the traditional design principle requires:

Airy Disk Diameter ≤ Pixel Pitch

Otherwise, "over-sampling beyond the diffraction limit" occurs—the Airy disk covers multiple pixels, causing system resolution to decline rather than improve.

Simulation research conducted by the CETC Electro-Optics Technology Co., Ltd. team revealed: For a mid-wave infrared (3–5μm) system employing an F/3 optical speed and a 7.5μm pixel pitch detector, at a wavelength of 4.8μm, sampling of the Airy disk "completely fails to resolve two points."

This means shrinking pixel pitch while ignoring optical diffraction limits is like using an ultra-high-pixel camera to take a blurry photo—when you zoom in, you only see sharper blur.

3. Manufacturing Process and Crosstalk: The Invisible "Internal Friction"

Shrinking pixel pitch also brings a series of device-level challenges:

These effects are further exacerbated in high-temperature operating environments—which are precisely the common working conditions for many electro-optical pods and outdoor surveillance devices.

4. The Non-Linear Cost Escalation

Finally, the concern that matters most to B2B customers: cost.

A comparative experiment conducted by a photonics industry research team on three pixel pitch systems (5μm, 8μm, and 15μm) revealed the following, under the premise of maintaining equivalent spatial resolution:

• The 8μm solution achieves a 9% system cost saving compared to the 5μm solution.
• The 15μm solution achieves a 19% system cost saving compared to the 5μm solution.

The cost impact of small pixel pitch exhibits a non-linear characteristic—once the pixel size falls below a certain threshold, every micron of reduction brings exponential increases in optical element precision, lens count, and assembly difficulty.

III. So, How Should You Select Pixel Pitch for Continuous Zoom Lenses?

The answer is: There is no single optimal pixel pitch, only the optimal match.

Option 1: 15μm Pixel Pitch – Performance-Prioritized

Better suited for scenarios demanding high detection, recognition, and identification capabilities, such as coastal defense surveillance and military reconnaissance. At the same F-number, 15μm pixel pitch provides higher signal-to-noise ratio and thermal sensitivity (NETD)—the foundation for "seeing farther and clearer."

Option 2: 8–10μm Pixel Pitch – Optimal Cost-Performance

This is currently the mainstream choice for continuous zoom systems. Compared to 5μm solutions, 8μm offers significant system cost advantages while maintaining manageable optical design difficulty, providing a good balance between SWaP and performance.

Option 3: 5μm and Below – Niche Applications

Suitable for very short-range, high-magnification fixed-field or short-travel zoom applications. However, for the telephoto end of continuous zoom lenses, current designs are still struggling with diffraction limit constraints.

IV. Practical Recommendations for System Integrators

1. Don't be misled by "pixel count": For continuous zoom systems, Thermal Sensitivity (NETD) and Instantaneous Field of View (IFOV) often determine actual detection capability far more than mere array specifications.
2. Demand F-number and pixel matching: Ask your supplier: "Has this lens's optical design been optimized for the target pixel size? Will Airy disk aliasing occur at extreme zoom positions?"
3. Balance "seeing clearly" vs. "seeing far": Small pixel pitch excels at close-range detail rendition, but when it comes to long-range target identification, larger pixel pitch often has the upper hand.

The infrared optics industry is undergoing a "pixel race," but the finish line should not be the accumulation of numbers—it should be the authentic improvement of system effectiveness.

For continuous zoom lenses, pixel size selection is a matter of systems engineering trade-offs—a multi-dimensional balancing act involving optical design, detector technology, mechanical structure, image processing algorithms, and cost control.

What fits best, is best.

Data sources: Public research results from Tianjin Jinhang Technical Physics Institute, CETC Electro-Optics Technology Co., Ltd., and other industry research institutions.

Related Product Recommendation: Our company offers a series of continuous zoom infrared lenses compatible with mainstream 12μm–15μm detector specifications, along with customized optical design services. Please contact us for technical selection consultations.