How do you know which fixed focal length to get?

iseeker

iseeker

Getting the hang of it
Nov 16, 2018
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Trying to save a bit of money by getting a fixed focal length for certain positions. Logging in to the web interface of my current cameras (see sig block) doesn't tell me the focal length when zooming; was hoping to use one of those as a test.

Is there a chart that suggests the correct focal length to get?
 
@looney2ns - what software shows you those types of values for the zoom? Not in my synology or logging in directly to the camera. Just has a zoom slider bar. Are these Blue Iris settings?
 
For the two Dahua cameras, if you hover over the slider used to change the zoom, it should show the actual value.
 
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iseeker said:
Trying to save a bit of money by getting a fixed focal length for certain positions. Logging in to the web interface of my current cameras (see sig block) doesn't tell me the focal length when zooming; was hoping to use one of those as a test.

Is there a chart that suggests the correct focal length to get?
Click to expand...

Hi @iseeker

You may also use the following for many of the 2MP 1080P Dahua cameras:

Here are the numbers ( theoretical ) that I calculated to the 100 ppf density level ( arc ):

Dahua IPC-HDW4231EM-AS starlight fixed lens 1080p 1920x1080
w/2.8mm lens FOV H 110 degrees: 10 feet { area covered 95.94 sq feet covered }
w/3.6mm lens FOV H 87 degrees: 12.65 feet { 121.43 sq feet covered }
w/6mm lens FOV H 51 degrees: 21.58 feet { 207.16 sq feet covered }

As this is for a 1080p you can get a rough idea by:
At the distance to 100 ppf, measure 19.2 feet wide - that will be the approximate FOV width measured from the camera. ( approx as I used Arcs to calculate )
 
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