Short answer
The smaller the lens's millimeter value, the wider the area the camera sees, but the smaller distant detail becomes. 2.8 mm sees a room or entrance wide, 4 mm is a little narrower and looks farther, and 6 mm and above are for distant targets such as corridors, roads and plates. If you are not sure what you want, a motorized lens lets you adjust the angle after installation.
What does the millimeter value of the lens change?
The millimeter value on a camera lens is the focal length. This value determines how wide an area the camera sees. A small value means wide angle, a large value means narrow angle. You can think of it like turning the zoom on a camera: the closer you zoom, the narrower the frame gets and the bigger distant things look.
Because the camera's resolution is fixed, this is a trade-off. If the same number of pixels is spread over a wide area, fewer pixels fall on each object. If it focuses on a narrow area, objects in that area get more pixels and are seen more clearly. A camera with a 2.8 mm lens at the entrance sees the door and its surroundings wide, but cannot read the plate of a vehicle 10 meters away.
The viewing angle in degrees depends not only on the lens but also on the sensor size. That is why the same 2.8 mm lens can give images of different widths on two different cameras. Looking at the horizontal field of view value on the technical datasheet gives a more accurate idea.
Where do 2.8 mm, 4 mm and 6 mm fit?
The matches below are a general guide. The exact choice is made according to the camera's distance to the target and what you want to see at the target.
- 2.8 mm: room, inside a shop, door entrance, small garden. Places where you need to see a wide area but not look far.
- 4 mm: medium-sized garden, housing estate entrance, store aisle. A balanced choice that looks a bit farther.
- 6 mm and 8 mm: long corridor, road running along a building facade, warehouse aisle.
- 12 mm and above, or motorized: parking lot entrance, plate reading, identifying a distant door.
What is a motorized (varifocal) lens for?
A varifocal lens is a lens whose focal length can be adjusted within a certain range (for example between 2.8 and 12 mm). On motorized ones, this adjustment is made remotely from the recorder or a computer rather than by hand. After the camera is mounted on a pole, you can narrow and widen the angle while watching the screen, and focus automatically.
A motorized lens is especially useful in three cases: places where the camera is mounted on a high pole and climbing up again with a ladder is hard, areas where the need may change over time, and installations where the exact distance cannot be estimated beforehand. The price is a higher cost than a fixed-lens model and a slightly larger camera body.
A motorized lens should not be confused with a PTZ camera. A PTZ camera pans left and right and tilts up and down, and zooms remotely. A camera with a motorized lens faces a fixed direction and only its angle is adjusted.
Expert note: Do not leave motorized-lens cameras at the narrowest setting after installation. At a narrow angle, the camera collects less light in the dark. Check the day and night images together and choose a balanced setting.
When should you consider fisheye and panoramic cameras?
Fisheye cameras are mounted on the ceiling and look downward, showing the whole room in a single image. In an open-plan store, café or waiting hall, a single camera can provide an overall view in place of several cameras. The image comes out round and warped; the recorder or software flattens it and splits it into several separate views.
The detail these cameras give is limited. People near the edges look small and warped, which is not suitable for identifying faces. That is why a fisheye camera is generally used to see the overall situation, and a fixed-lens camera is added separately at critical points such as the register and the entrance.
Panoramic cameras, on the other hand, place several sensors side by side and join a wide horizontal area into a single image. They are used in long areas such as parking lots or factory grounds, and their price and recording load are higher than a single-sensor camera.
A practical way to find the right lens
First answer two questions for each camera point: how many meters away is the target from the camera, and what do I want to see there? Noticing a movement, recognizing a person and identifying a face need different numbers of pixels. For identification, many more pixels must fall on the target, which means a narrow lens or a high resolution.
Then, with a camera distance tool, calculate how wide the image will be at the target distance with the lens and resolution you are considering, and how many pixels will fall on the target. This calculation reduces the chance of having to replace a camera after installation because of the angle.
Finally, if possible, do a test on site. Holding a camera temporarily at the same spot and seeing the image on a screen immediately shows whether the calculation matches reality.
Common lens mistakes
The most common mistake is trying to see everything with a single camera. Putting a wide-angle camera at the corner of the garden and wanting it to cover the door, the parking lot and the street all at once produces an image with no useful detail in any of them. One wide-angle camera for the overall view and a separate narrow-angle camera for the critical point gives a better result.
Another mistake is putting a narrow-lens camera too close. If a camera with a 12 mm lens looks at a door two meters away, it sees only a chest or a door handle. Someone passing in front of the camera also stays in the frame for a very short time.
The camera's tilt angle also affects the lens choice. If you mount the camera too high and make it look down with a narrow lens, you see the top of the head instead of the face. At points where identification is wanted, the camera is placed as close to eye level as possible, looking at the target slightly from above.
What to watch for in an outdoor lens in Şanlıurfa
In dusty air, the front of the lens gets dirty quickly. Narrow-angle lenses are more sensitive to this dirt, because a small speck of dust blurs a large part of the frame. Models that have a sun shield or can be placed under an eave reduce how often the lens needs cleaning.
In summer afternoons, the sun shines directly into cameras on west-facing facades. For west-facing cameras, choosing models with wide dynamic range (WDR) support and adjusting the angle so the sun is not in the frame saves you from glare and dark shadows.
During the site survey, Desa Bilişim measures the distance for each point and adds the lens recommendation, based on this measurement, to the written quote.
Frequently asked
Is 2.8 mm or 4 mm better?
Which is better depends on the target. If you want to see the whole of a narrow area, 2.8 mm is suitable; if you want to see a slightly more distant point more clearly, 4 mm is suitable. The best way is to measure the distance between the camera and the target and decide from that.
How many mm of lens do you need to read plates?
The lens needed varies with the camera's distance to the vehicle and the lane width. In most cases a camera with a narrow-angle or motorized lens, positioned specifically for the plate, is needed. It would not be right to give a definite value without measuring the distance and doing the calculation.
Can the angle of a fixed-lens camera be changed after installation?
The direction the camera faces can be changed, but the width of view does not change. If you want a wider or narrower image, either a camera with a different lens is installed or a motorized-lens model is chosen from the start.
The right angle, the right distance
Let us measure your camera points on site and state the suitable lens for each one in the written quote.
