Understanding the Specifications for IP Cameras

Technical Note: Understanding the specifications so you can get the best performance from your IP Cameras

A combination of focus, depth of field, lighting, dynamic range, and field of view determines the quality of the picture.  Some of these things are interrelated. Here is a summary of the important specifications for IP Cameras

The Lens:

There are a number of different types of lenses.  There are fixed focal length, and variable focal length lenses.  There are also manual iris and auto-iris lenses to choose from.  Some lenses must be adjusted at the camera, and some new lenses can be adjusted remotely.  There are also new p-iris lenses that provide a number of new functions.  Each of these lenses requires some different adjustments.  

Fixed Focal Point Lens: These lenses view a fixed area and you can’t adjust the zoom.  They are available with manual and auto iris control.

Variable Focal Length Lens: Also called variable lenses, allow you to adjust the field of view by adjusting the focal length setting.  These are better lenses since they allow you to make adjustments so that you are viewing exactly what you want.  They are available with manual or auto iris.

Iris Control:  The iris can be controlled manually or automatically.  While it is true that a smaller iris opening often means sharper images, too small an opening may blur an image due to an optical effect called diffraction. This problem can be seen in bright outdoor situations when a camera closes the iris too much and light is diffracted or spread over many pixels.  The smaller each pixel is on an image sensor, the more of a problem diffraction becomes because the diffracted light affects more pixels. This can typically happen in cameras that use an automatic DC-iris lens in combination especially with megapixel sensors that have small pixels. (While a megapixel sensor has more pixels than a standard VGA 640x480 image sensor, the size of each pixel on a megapixel sensor is often smaller than the size of each pixel on a VGA image sensor.) 

Manual Iris Lens: These lenses are usually used indoors and allow you to adjust the iris opening.

Auto-Iris Lens:  The iris of the lens is adjusted by the camera.  The iris opening is adjusted automatically when more or less light is required on the sensor of the camera.

P-iris lenses:  P-Iris is a new type of iris control that is both automatic and precise.  It works in conjunction with the camera to improve the quality of the video.  Unlike a DC-iris lens, the main task of the P-Iris control is not to continuously adjust the flow of light through the lens.  The primary objective of P-Iris is to improve image quality by enabling the optimal iris position to be set so that the central and best-performing part of the lens is used most of the time.

The P-Iris works with the electronics of the IP camera.  It not only adjusts the iris, it also adjusts the gain (amplification of the signal level) and exposure time.  This allows it to manage slight changes in lighting conditions and to further optimize an image. This allows the optimal iris position to be maintained as long as possible. In situations when the preferred iris position and the camera’s electronic processing capabilities cannot adequately correct the exposure, a P-Iris camera will automatically instruct the iris to move to a different position. In dark conditions, for example, the iris will fully open. In bright situations, a camera with P-Iris is programmed to limit the closing of the iris to a position that avoids diffraction or blurring, as explained earlier. Hence, in all lighting conditions, P-Iris can automatically make adjustments to deliver optimal image quality.

Take a look at the two pictures below.  You can see the benefits of the p-lens.

 
Standard auto-iris

P-Iris

At the moment Axis is one of the few IP camera manufacturers that have this new functionality.  The Axis P1346 and P1347 are examples of cameras with p-iris lenses.

Megapixel Lens: Megapixel cameras require megapixel lenses. These lenses are much clearer than the standard CCTV analog camera lens. They cost more so if you see two megapixel cameras with the same number of pixels but one cost much less, they are probably using a less expensive (not as good) lens. Take a look at our article on how High-Resolution, Megapixel Cameras are not all Alike.

Other things to consider:

Field of View:  Before adjusting the focus, make sure you are viewing exactly what you want.  For example if you are viewing a doorway and want to be able to identify a person’s face, you need enough pixels across the person’s face.  The wider the view the fewer pixels are available.  If you zoom in too much, you may miss something that is not in the field of view.  You need to adjust the lens so that it is viewing just the entrance area.  Once you have the field of view selected, you will then need to make sure that everything you want to view is in focus.  Focus is affected not only by the lens but also the iris, which affects the depth of field.

Exposure Time or Shutter Speed:  Another way to adjust the amount of light that reaches the sensor is to open the shutter different periods of time.  The longer the shutter is opened the more light is on the sensor.  But, if there is motion the image will be blurred when the shutter is opened too long.  The faster the moving picture, the shorter the shutter speed should be.

Depth of Field:  The depth of field is the range of distance where objects are still in focus.   The iris affects the depth of field.  In general the smaller the lens opening (or aperture) the greater the depth of field, while the wider the lens opening the smaller the depth of field.  It would be great if you could close the iris but then you may not get enough light on the sensor, so you must make some adjustments and compromises to get it as good as possible.

Having good depth of field—where objects at different distances from the camera are in focus simultaneously—is important in many surveillance applications as it allows more of a scene to be clearly visible.

Camera Gain:  Cameras include amplifiers that improve the video performance when there is low light.  This works well until the electrical noise affects the image.  Too much amplification reduces the quality of the video.  The better the amplifiers in the camera the less noise will be seen.   Some IP cameras like the ones from IQinvision, do not rely on the iris but rather make all the adjustments electronically.

Image on the left has more random noise than the image on the right

Dynamic Range
The dynamic range of a camera is a measure of the minimum and maximum light the camera can see in one frame.   Wide dynamic range is helpful when you are looking at a person against a very bright background.  Sony has introduced cameras with very wide dynamic range that allows you to see the image on the top.

Camera Low Light Sensitivity:  A camera that has very good low light sensitivity will operate better at low light conditions.  This means that even when there is a low light level, you may not need to open the iris all the way.  This will improve the depth of field, even when there is very little light.  Cameras such as the Axis P3344 and the IQeye IQ752 are examples of cameras with good low light sensitivity (0.05 lux minimum).

Now here’s how to adjust a Variable Focal Length, Manual Iris lens

Conclusion
As you can see getting the best picture requires many factors and adjustments.  Focusing the lens is not the only thing to consider.  The type of lens, the camera performance, iris opening, and shutter time all need to be right to get the best video image. 

Need some help selecting the right lens and IP camera, just contact us. We will be happy to help. 1-800-431-1658 (in the USA) or 914-944-3425 (outside the USA) or send us a message.