Quality Megapixel lenses(1): Differentiation

As video surveillance evolves, footage has more resolution and greater detail than ever before. HD cameras have benefited from component breakthroughs in image sensors and processors, which support the current crop of megapixel cameras and even the hottest 4K ultra high definition (UHD) trend. The bottleneck for achieving even more pixels is dependent on the lens. With so many lens providers on the market, how do integrators and installers identify “true” megapixel optical lenses for HD surveillance?

By now, it is common knowledge that a megapixel camera needs a megapixel lens to reach its full HD potential. Surveillance lenses mainly come from Japan and China, with some providers in Korea and the U.S. Looking at the top lens brands by their country of origin, Theia and ImmerVision represent Europe and North America. Japan is home to Tamron, Fujinon, Computar, Tokina, Kowa, Pentax, Speacom, Avenir, U-Tron, and more. Korean lens manufacturers do not have the market share or sales to topple Japanese lenses, but Daiwon is blazing a path for Korean lenses.

Finally, while Chinese lenses lag behind Japanese ones in quality and quantity, China's market share has steadily increased over the past five years. Notable improvements have also been made in lens technology over the past few years. “Quality and performance in optics have been improved due to the integration of electronic processing. Lens manufacturers have been challenged to create lenses that provide higher quality images at lower costs,” said Alessandro Gasparini, ChiefCommercial Officer of ImmerVision.

 

“In recent years, software specialists began to work with lens manufacturers, resulting in a drastic evolution of lens technology. Innovations like P-Iris control, dewarping, and post-capture processing are a direct result of this collaboration. With IP cameras, digital data can be manipulated and enhanced. A decade ago, optical designers viewed distortion as a defect and created lenses with no distortion. Today, distortion can be manipulated to enhance the performance of the lens. Combining optics with electronic components creates more possibilities, better performance, and is beneficial to the end user.”

Identifying the Right Lens
Based on spec sheets, it seems all lenses are equally good for any application. However, the top lens providers have maintained market share because of a unique advantage in production or product development for specific environments. This specialization is necessary to survive in video surveillance.

 

Brands	HD Lens Types	HD IR Lens	HD Fisheye	HD P-Iris	HD Defog	HD  OS-Tech
Tamron	1.3,3MP	■		■
Fujinon	1.3, 2, 3, 5, 8MP	■	■	■	■	■
Computar	1.3, 3, 5MP	■		■
Tokina	1.3, 3, 5MP	■	■
U-TRON	1.3, 3MP	■
AVENIR	1.3, 3MP	■
Daiwon	1.3, 2, 3MP	■	■	■
RICOH	1.3, 1.6, 2, 3, 5MP	■	■		■
EVETAR	1.3, 2MP	■	■
Phenix	1.3, 3MP	■
Theia	3, 5MP	■		■

 

Table 1 compares the main lens providers by functionality, which indicates the direction of each brand's R&D and core competence. Besides fixed and variable focus, or automatic and manual aperture, which are key buying concerns for surveillance lenses, the chart also looks at day/night IR lenses and whether they feature a programmable aperture, better known as “P-Iris” functionality.

Another deciding factor is if the lens is a defogging one. Many breakthroughs in consumer SLRs are being introduced for high-resolution surveillance lenses. This class of high-end lenses has a clear advantage for surveillance footage, which stands to benefit from mature still-camera lens developments. Some next-generation features include eliminating vibration internal focusing, color dispersion, hushed motors, and other optical advances.

Key Technologies/Features that Differentiate Lenses

Aspherical lenses
The use of aspherical lenses are in great demand for high-resolution surveillance. They have good light transmittance and low refraction, which results in all light being focused on a single point. These lenses also help to reduce image distortion. Common forms of image distortion include barrel distortion where images are curved outward, or pincushion distortion, where images are curved inward. Aspherical lenses make images appear sharper and are typically used for wide-angle or ultra wide-angle lenses.

Low Dispersion or Ultra-Low Dispersion
Lenses with low (LD) or ultra-low dispersion (UD) are often used to reduce chromatic aberration, which increases color reproduction in the images, as they refract light in a way that maintains the wavelength for true color. Image color matches the object almost perfectly. Video surveillance products typically deploy LD lenses, while UD lenses are used for digital cameras. UD lenses are more common among Japanese products.

Lens Coatings
Coating the lens can reduce the surface's reflectiveness, resulting in images free of ghosting, glare, and lens flare. Coatings also improve light transmittance. All surveillance lenses are coated, but each manufacturers' technique can differ significantly.

Therefore, knowing how well the coating is done will affect component selection. Most users only know whether a lens is coated or not, but they do not understand the different types of coatings. The major types of lens coatings include nano coating, integrated coating, subwavelength structure coating, multi-coating, transparency coating, broadband anti-reflective (BBAR) coating, and high-fidelity transfer coating. Not all coatings are used for surveillance; BBAR and nano coatings are most commonly used for surveillance, while the rest are used for digital cameras.

Fluorite Lenses
Fluorite lenses are commonly used for high-end cameras with zoom lenses and high-resolution telescopes. They have extremely low refraction and dispersion, so the lenses can zoom in without image dispersion. High-end Japanese motorized lenses are often made of fluorite.

High Refraction Index Lenses
These lenses are highly specialized, using polarized lenses to correct optical distortion. This makes the camera body lighter and is frequently seen in digital cameras or surveillance onboard lenses. However, this is not ideal for surveillance applications, resulting in little development for security lenses.

Diffractive Optics
Diffractive optics refers to lenses with double or triple layers. This limits the imaging lights from producing unnecessary radiant flux and reduces dispersion caused by multiple lenses. The lens layers are closely fitted, resulting in low chromatic aberration and a more compact size. This lens technology is often applied in small varifocal lenses.

Dual Super Aspherical Lenses
Dual super aspherical (DSA) lenses are fairly specialized. Made by joining two aspherical lenses together, DSA lenses improve image clarity and allow cameras to be more compact. DSA lenses are typically used in digital cameras.

Apochromatic Lenses
Apochromatic lenses are commonly used in digital cameras as well. They are able to better correct chromatic aberration as they allow more colored light to pass through the lens. This type of lens in surveillance applications is commonly seen in LD and aspherical lenses.

Multifocusing
Multifocusing lens technology is one of the latest developments that has been successfully implemented in still cameras since the second half of 2011. This technology allows a lens to have multiple focuses, so even if a shot is blurry, the image can be refocused afterwards during playback or when images are being reviewed. In terms of surveillance, this proves to be a significant breakthrough for forensic evidence, which will certainly be seen in the near future. Lenses that are LD or spherical could use this technology.