A lens with auto back focus is essential for image quality. “For a fixed dome, what's really important is a good lens that's easy to adjust,” Corrall said. “You can go to any focal length, and it will stay in focus. That's important to installers and makes sure the focus is always crisp.”
Lens
A lens with auto back focus is essential for image quality. “For a fixed dome, what's really important is a good lens that's easy to adjust,” Corrall said. “You can go to any focal length, and it will stay in focus. That's important to installers and makes sure the focus is always crisp.”
The dome's lens must also have enough resolution to support the image sensor. As higher resolution is seen mostly in fixed network domes, standard definition (SD) lenses will not focus light properly on image sensors with more pixels. This will result in blurred edges and loss of corner detail.
Full high definition resolution at 1080p is 16:9 or 2.1 megapixel, which is a wider aspect ratio compared to 4:3 in SD. “The corner detail needs to have sufficient TVLs,” said Allen Yang, PM at Etrovision Technology.
Bubb le Trouble One of the easiest ways to distinguish a dome's quality is by looking at the dome bubble. “Bubbles are made of either polycarbonate for superior strength or acrylic for superior clarity,” Crosby said. “Acrylic allows for the greatest performance with IR illumination. Both low-light and IR performances are affected by any tinting that the bubble may have. The more tinted, the more covert, but the lower the sensitivity.”
Under normal conditions, customers prefer smoked bubbles, but clear domes are accepted for outdoors, Atsushi said.
Corrall agreed, noting that many people do not expect an effect from smoked bubbles. “It can be like viewing through sunglasses.”
The bubble should be as flawless as possible, so the camera has a clear view no matter where the lens is pointing. “Under high magnification, a dome cannot lose focus,” Huang said. “A commercial bubble may work at 20x, but does not work at a higher magnification.”
A bubble's material determines where it can be used. “A town center is different from a petrochemical site; it could be polycarbonate, lexan or stainless steel,” Pigram said. “Whether it's curved, plastic or glass makes a big difference for the optical quality.”
The bubble must be easy to install as well. Some vendors include a cord or insurance line attaching the bubble to the back box, so it does not accidentally get dropped and break.
Product Adopted:Cameras