Addressing limitation issues
Much has already been written about the factors affecting the adoption of

4K as a standard in the security industry.

These typically include the cost of infrastructure and hardware.

However, technological and market advances are addressing these limitations

with the introduction of H.265 compression and the rapidly declining price of

4K monitors.

With these advances, 4K is on course to become the next big video surveillance

standard within two to five years.

High performance lenses for high performance systems
But not much has been written on the importance of finding compatible

high performance lenses for use in these emerging 4K systems.

Without a compatible one, the lens will become the limiting factor in the system,

throttling the overall image resolution performance and effectively wasting

the investment by delivering sub-4K images.

There are only a few commonly used 4K sensors in the security market today.

These sensors are not much larger than those used for HD

or higher megapixel resolution cameras,

but their pixel count is significantly higher and the pixel sizes

they generate are necessarily much smaller.

For example, while a typical 5-megapixel sensor is 1/ 2.5” in size

with 2.3 micron-sized pixels, the IMX172 4K sensor from Sony is 1/ 2.3” in size,

with 1.55 micron-sized pixels —

that’s 33 percent smaller than the pixels of the 5-megapixel sensor.

Meanwhile, the Sony IMX226 sensor is larger at 1/1.7” in size

with 1.85 micron-sized pixels—19 percent larger than the pixels

of the IMX172 sensor, but still 20 percent smaller than

the typical 5-megapixel sensor pixel size. (Refer to image 1)
 
The pixel size also dictates the level of contrast in line pairs per millimeter

that the lens is required to resolve. For example, the smaller 1.55 micron-sized pixel requires

the lens be able to distinguish 300 line pairs per millimeter (lp/mm),

while the 1.85 micron-sized pixel requires the lens distinguish 270 lp/mm.

Finding a lens with the power to resolve the smaller size pixels and deliver

adequate contrast is a challenge.

The focal plane spot size of the lens must be comparable or smaller than

the pixel size on the sensor (Figures A and B);

otherwise, the rays of light trained through the lens will fall off the pixel

and the image will be muddy, instead of crisp.

The availability of lenses which can resolve these small 4K pixels is limited right now.

They typically require a more complex lens design. The design requires

a greater number of more complicated elements such as plastic molded aspheres.

They need better glass, plastics and coating materials.

Adding IR correction for day/night performance in 4K resolution presents

further design, manufacture and cost challenges to work through.

Camera companies have, in some cases,

paired fixed focal length machine vision lenses with their newly-minted 4K cameras.

Varifocal lenses, which give the installer more control over the fine-tuning field of view

and fewer lens types to order, are even more difficult to find right now

with acceptable 4K performance, especially in sizes compact enough to

fit in reasonably-sized dome cameras.

Smaller vs larger image sensors
As one can imagine, the smaller sized 4K pixels cannot physically collect

as much light as those of the larger pixel size sensors.

This reduces image quality in low light conditions, and would lead one to believe

that the industry would be more inclined to adopt the larger 1/1.7” pixel-sized sensor.

However, a larger sensor requires larger lenses, making both sensor and lens

more expensive.

So from this, we can predict that the smaller 1/2.3” 4K image sensors will be selected

for 4K economy-line cameras; while the larger 1/1.7” sensors may be reserved

for top-end,

“high performance” 4K cameras.

The 4K cameras and lenses are still only made in low volumes,

making them more expensive.

These higher performance, higher resolution lenses support smaller pixels.

They also increase the complexity and cost of lenses.

 However, without these new lenses,

4K is in danger of over-promising and under-delivering.

Implementation of 4K systems
The selection of 4K-rated hardware and systems, when used in key applications,

can make an easily supported business case. Alignment in purpose

during the selection of systems

 — both hardware and software —

for key applications can make the difference

in justifying the implementation of 4K video systems today.