Here is a link to an online lens calculator that will help you
learn about various lens sizes and will help you decide what lens
is appropriate for your camera.
Please note that not all lens sizes are available in every
camera. For example, very wide field of vision lens do not always
work in a night vision camera with LEDs as the LEDs will interfere
with the wide view.
Which Security Camera Lens Should I Use?
How far you need to see will determine what
security camera lens you should use to best fit your application.
A 4mm lens will give a 70 degree angle of view with 35 feet of
facial detail. This works great for residential or small office
security camera applications. If you need to see further you would
go with a higher powered lens. Keep in mind that the further you
want to see will narrow the field of view of your picture.
A rule of thumb is that a 8mm lens is like a 4mm
lens zoomed in 2 times. Similarly, a 16mm lens is like the 4mm
lens zoomed in 4 times. For example, a 16mm lens would give you
about a 15 degree angle of view focused at 35 ft.
What If I Do Not Know Exactly How Far I Need To See?
Instead of going with a fixed focus lens you can go with a
varifocal lens. With a simple adjustment you can manually zoom in
or zoom out and focus the camera to the exact distance needed to
get a clear picture. Varifocal lenses come in all different sizes:
(3.5-8mm; 9-22mm; and 5-50mm) just to name a few. This is the best
option for large commercial applications because you can adjust
the focal distance to what works just right.
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A Pan Tilt Zoom camera (PTZ) allows you to pan (back
and forth), tilt (up and down), and zoom (focus in and out) your
camera remotely. The PTZ is controlled using a remote PTZ
controller or you can control it through most DVRs (look for PTZ
support). The disadvantages of a PTZ camera is that they are very
expensive (usually around $1000 without the controller). And all
the moving parts make it susceptible to wear and breakdown.
There are some new digital versions of PTZ cameras just coming on
the market that have no mechanical parts. These PTZs are very
promising but are still a little too expensive to be practical for
most uses. PTZ cameras require a data cable to be run to the
camera in addition to the video and power cables. Unless you have
a person who is watching the scene and adjusting the field of view
of the camera based on what is going on its not as useful. Most
times you are better off buying more of the non-PTZ cameras to
continuously cover the area rather than a PTZ.
What is the difference between no iris and auto iris?
The iris controls how much light is let into the camera lens.
In the old days, cameras came with no iris control. If you needed
to control the light levels you would have to purchase a special
lens. Nowadays, most cameras come with automatic shutters which
perform the same function as the iris - controlling how much light
is let into the camera. Unless you have an application with
extreme light levels (like at a beach) you probably won't need a
special lens with iris control.
Lux and low lighting chart
Lux and low lighting chart
Condition
Illumination
Details
(FTCD)
(LUX)
Sunlight Full Daylight
Overcast Day Very Dark Day Twilight Deep Twilight
10,000 1,000 100 10 1 .1
107,527.00 10,752.70 1,075.30 107.53 10.75 1.08
Daylight Range
Full Moon Quarter Moon Starlight Overcast Night
.01 .001 .0001 .00001
.1080 .0108 .0011 .0001
Low
Light Level Range
During the day the
amount of illumination reaching a scene depends on the time of day and
atmospheric conditions. Direct sunlight produces the
highest-contrast scene, allowing maximum identification of objects.
On a cloudy or overcast day, less light is received by the objects in
the scene, resulting in less contrast. To produce an optimum camera
picture under the wide variation in light level (such as occurs when
the sun is obscured by clouds), an automatic-iris camera system is
required.
Typically, scene illumination measured in foot-candles
(ftcd) can vary over a range of 10,000 to 1 (or more), which
exceeds the operating range of most cameras for producing good quality
video images.
The chart above summarizes the light levels occurring
under daylight and these low light level conditions. The equivalent
metric measure of light level (lux) compared with the English (ftcd)
is given.
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