Fixed vs Varifocal Lenses

Published on August 7, 2019 by Matt Garnham in Blog Posts on Security Cameras

There are 2 different categories that security camera lenses fall into:

  1. Fixed Lens or Fixed Focal Length Lenses
  2. Varifocal Lens of Varifocal Zoom Lenses

They both serve a purpose – read on to find out which one is better for your particular need.

Security Cameras with Fixed Lens

Simply put, you get what you are given. As the camera comes out the box, there is no adjustment necessary. Quick to install – attach to the wall/ceiling, connect the wires and away you go.

The advantages of these are easy to see – the cameras are quicker to install and a little more cost effective. The problem comes when you end up recording areas that are of no interest at all.

Security Cameras with Varifocal Lens

Varifocal lens cameras really give you the opportunity to make a huge difference in the effectiveness of your security camera system.

While they are often a little more expensive, they are infinitely adjustable between their widest angle of view and most zoomed in (telephoto) angle of view.

A Couple of Photos to Demonstrate

It’s a lot easier to demonstrate this concept with photos instead of using text. I’m going to try to do just this! The situation is that a customer located in the same city as us here in Southern Florida is concerned about people using the side of their house. Pool, landscape, boat techs, gas guys all regularly use the side of the house. This side access gate is hidden from view of both the front and the back of the house.

A typical fixed lens camera such as our Open Dome Turret Camera with 3.6mm lens would produce an image that looks like this:

From a Fixed Lens

Orange Security Cameras Golden Rule

Yes, this looks like a nice photograph, and you can see the side access gate and even the pool equipment. The problem is that because your pixels are spread over such a wide area, you are unlikely to identify a perpetrator. Large portions of the image are being wasted on irrelevant things.

What do I mean by wasted? Simple really. Large portions of the image are used for things that are never going to be any use:

  • The sky – aliens a concern? Nope – this area is wasted
  • The wall of the house – can someone come through a solid block wall? Nope – this area is wasted
  • The hedge – can some come through that super thick hedge with fence in the middle? Nope – again, this area is wasted

In reality, only about 20% of the available pixels are actually being concentrated on the bit that matters – the side access gate. To put it another way, the full image is around 2 million pixels. Less than 400,000 are being used for the gate.

From a Varifocal Lens

Ok – let’s now look at the same thing, but from a camera with a varifocal zoom lens. This image comes from one of our longer range Bullet Cameras:

Orange Security Cameras Golden Rule

You can immediately see that the clarity and the definition, for the area that is important, is in a totally different ballpark. This is because instead of having less than 400k pixels on the side access gate, you now have a little over 2 MILLION pixels! That’s 5 times more.

This is achieved by taking a varifocal lens camera and adjusting it such that it is filming exactly what is required…and no more.

This is the power of Security Cameras with Varifocal Zoom Lenses

Can you Not use a Longer Fixed Lens?

Can you not just manage with a fixed lens camera but with a longer lens, I hear you ask. Great question and great observation! Yes, in theory you can. In practice, however, the above image is achieved using one of our Bullet Cameras with 5-50mm Lens and ended up being set at about 27.85°…and I’ve not found someone selling a fixed lens camera with that particular option!

What About Just Moving the Camera Closer?

Another sensible question. Unfortunately, in most cases you can not get the camera in the right position. In the example posted above, there are 2 reasons why this wouldn’t work. One practical and the other aesthetic.

  1. Practical: by the time you got the camera close enough to achieve the type of image you are after, the angle of view would end up not being straight on looking at people. It’s much harder to identify people with a profile shot than it is a head on shot
  2. Aesthetic: the customer had another camera positioned behind this camera but facing the other direction. He wanted the cameras to be installed next to each other to reduce the visual impact. This really meant that there was only possible position to put the camera.

As you can see, while there are a number of different options available to that might work “in the lab”, it’s really not practical to get the best results without varifocal lenses.

What about Multi Megapixel Systems?

This is a very common question we are asked about this topic. It’s straying little off topic – perhaps I will write a more in-depth article on this subject in the future. However, simply put, the cameras are more expensive, the recorders are more expensive, the hard drive space needed is larger so more expensive, you still don’t actually have the pixel density required…and you’re still wasting pixels, data and hard drive space. That’s not to mention that often, higher resolution cameras work less well at night.

Digital Zoom?

Another common misconception is that you can do the same thing with digital zoom. Again, rather off topic and the subject of another future blog post.

Summary

When planning a security camera system, I think of cameras in 2 categories:

  1. General Overview Cameras
  2. Cameras for Identification

The first of the categories is the equivalent of the fixed lens camera. They are used to give you a general overview of the area – they allow you to see what is going on, but are exceptionally unlikely to allow the authorities to get a prosecution. The first example image above would be great if the camera feed was constantly monitored and the guard wanted to know whether there was a person there.

The second of these categories is the equivalent of the varifocal lens camera. They allow you to zoom right in to get identification. When the rubber hits the road, this is what REALLY matters. Can you take an image, give it to the Police and expect a prosecution. Clearly nothing is guaranteed, but it is more likely that with a varifocal lens camera, setup correctly, will get you this prosecution.

You may also find the Orange Security Golden Rule interesting in providing further information on this subject.


about the author: Matt Garnham
Security Camera expert for many years. He is the founder and owner of Orange Security. Started life in the security industry in the UK. Relocated to Southern Florida and Orange Security was formed.

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