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| Lenses for Megapixel IP Cameras |
What lens should I use for my IP Camera? Determining the right lens can be complicated
and assuring that you get the right one requires some care. This is a very important part of your IP camera system. If you get a megapixel IP camera but don’t
get the right lens you are wasting your money.
Many IP cameras
come with lenses. For example the Axis
P1354 comes with a 3 mm to 8 mm lens (100° - 34° horizontal field
of view). How do you determine if this will actually
work in a specific application? First
make sure you know what the angle or mm of the lens should be. The higher the mm numbers the lower the angle
and the more magnification you will get.
It’s best to use the lens angle that is provided by the manufacturer
instead of the mm of the lens since the angle can vary based on the size of the
sensor.
Lens Angle
By measuring the field of view and how far away the camera
will be from the area you want to view, you can calculate the angle of the lens. To calculate the angle of the lens required
you need to use trigonometry. Don’t get
upset, I slept through this class in high school as well. I do remember my teacher saying, “You’re
going to need this someday”, and me thinking, “Yeah, right”. There are some calculators on line that can
make this job easier. Here is a review
of the basics.
First we want to use
the horizontal field of view rather than the vertical field of view, so let’s
image we are looking down on the camera.
We split the triangle in half to get a right triangle.
Then we can use the tangent function to calculate all the
dimensions and angles.
The tangent (angle) = Opposite / Adjacent
In this case the dimensions we use are ½ the field of view (FOV)
and ½ the angle, so the equation is:
The tangent (½ angle of the camera lens) = ½ the FOV / Distance
from camera to FOV
Now we can calculate everything we need. For example if the distance to the field of
view is 100 ft. and the FOV is 50 ft. Here’s how we get the lens angle:
½ Tan(lens°)
= ½ 50 / 100.
Tan(lens°) = 2 x(½ 50 / 100)
Now I go to my on
line calculator at http://www.pagetutor.com/trigcalc/trig.html
and enter 25 where it says “Side A”, and then 100 into the “side B”, I get 14.04°.
Then 2 x 14.04° = 28.08°.
And of course, if you know the lens angle and want to
calculate the FOV based on a certain distance, you can do this as well using
the same equation and calculator.
OK, your head hurts.
I understand. Just take two aspirin
and call us and we’ll do all the calculations.
Other Specifications
Once you know the type of lens required you also need to
review all the other lens characteristics for a specific application. We reviewed all the lens specifications in our
technical article Megapixel
Lens for Megapixel IP Cameras, but here is a summary.
Lens Format or Size:
the lens size should be larger than the sensor of the camera.
Lens Mount: There are 2 types of mounting formats used in
IP cameras, C and CS type. Make sure the
lens you select matches the camera mount.
Iris: There are manual adjustable irises, auto-iris
and the latest p-iris. If the lens is
used indoors, you usually can use a manual iris camera, but outdoors you need
an auto-iris lens. If there are
challenging lighting conditions then the p-iris is a good choice.
If you are using a
megapixel IP camera then you must consider some additional specifications such
as lens resolution, depth of field, iris control, and distortion, aperture and IR
light capability. These are all very critical to assuring that you get the
video that you expect. If you get an
inexpensive lens you certainly won’t be happy with the video.
Yes, this is all complicated so please contact us for
assistance. We will review your
objectives and make sure that your complete IP camera system performs exactly
as you expect. Please call us at
914-944-3425 or just use our contact
form.
