CCTV Lens Finder App Tested

By John Honovich, Published Nov 11, 2012, 12:00am EST

Figuring out the right lens needed for a specific camera location can be difficult, especially if you want to monitor something that is not close to the camera. Do you need a 10mm lens, a 30mm lens or perhaps even a longer one? In this note, we review a 99 cent CCTV Lens Finder iOS application [link no longer available] that lets you find the exact lens length with your iPhone or iPad's built in camera. We conclude with a test video examining the entire workflow.

[UPDATE: This app is no longer available and we cannot find any replacements or alternatives.]

Basics

The app lets you take a photo of the area you want to monitor. Keep in mind that the photo should be taken from the spot where the camera will be mounted. Then, you can digitally pan / tilt and zoom the image to identify the correct FoV for your shot.

Key limitations include:

  • Maximum FoV width is 45.2 degrees, too narrow for most surveillance shots (which are often 50 - 80 degrees). However, for wide shots, such an app is likely not necessary as most cameras come with varifocal lenses that cover that range. [Note: this restriction is a function of the built in camera.]
  • The app only has options for 1/4", 1/3" and 1/2" imagers. This will create slight errors in lens length for the increasingly common 1/3.2" and 1/2.7" inch MP lenses available today.
  • No Android version.

That noted, let's look at a practical example. Imagine you want to mount a camera on a building wall like so:

mounting location

This camera will capture cars and license plates entering into the parking lot.

area of interest

You need to figure out what the right lens length to cover this area is. You take a picture and load it into the application like so:

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full finder

Then use the controls to crop the image to the area of interest:

 zoomed

The result is that the app tells you in seconds that a 50mm+ lens is needed. This makes it easy to determine that you will need an 8 - 80mm lens.

Below is a video that puts all of this together:

For 99 cents, this is a nice niche application that can not only document but verify the correct lens length for long range cameras.

[UPDATE: This app is no longer available and we cannot find any replacements or alternatives.]

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