new camera : F and lens

[fa355115]

I want to buy a new IP camera for monitoring my garden, day and night, like Dahua ...
I always see the resolution (This is for me the picture quality, details), but also the Focal and Lens like

Focal Length 3.6mm(2.8mm,6mm optional)
Max Aperture F2.0(F2.0/F2.0)


What is really the Focal, is it better to have the 2.8mm or the 6mm ?
What is the Max Aperture ?

How are those 2 parameters playing in the game ?

MAny thanks !

 

[looney2ns]

Focal length is expressed in mm and a higher number means a bigger zoom, while a lower number mean the lens can be used for wider shots.

Max aperture is how much light is let into the sensor, the lower the number the more light collected. Better night vision.

This cam is great at night and day. Dahua Starlight Varifocal Turret (IPC-HDW5231R-Z)

 

[aristobrat]

There's a cool website that will show you the differences between focal length:
Camera Calculator / Design Software

Like @looney2ns said, as you increase the size of the focal length, the width of what your camera sees decreases, but the detail in what it sees increases.

In the examples below, the guy is standing 30 feet away from the camera. Check out how blurry he is on a 2.8mm lens, vs a 12mm lens. But also note how the width of the field-of-vision decreases between 2.8mm and 12mm.

2.8mm at 30 feet:


3.66mm at 30 feet:


6mm at 30 feet:


12mm at 30 feet:


What's great about the camera that @looney2ns linked to is that it's varifocal. You can set the focal length (via the camera's web interface) to just about anything between 2.7mm and 12mm. You basically zoom it to give you the perfect view for what you're pointing it at, vs. being stuck with whatever view a camera with a fixed 2.8/3.6/6/12mm lens gives you.

 

[aristobrat]

How are those 2 parameters playing in the game ?

IMO, for cameras at night, the parameter that has the biggest impact on image quality is the size of the image sensor.

The Dahua Starlight (and Hikvision Ultra Low-light) model cameras all have the bigger Sony STARVIS image sensor inside of it. These cameras also have have fewer pixels compared to most other cameras. Fewer pixels and a bigger image sensor means that each pixel can capture more light. In almost all situations, this results in great image quality during the day, and an image quality that can't be beat during the low-light situations (like night) unless you have bright lights on.