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What is a fixed lens and when should I use one?
Fixed lenses usually cover wide angle views regardless of the distance to the subject. If you have a camera in the corner of the room or if you are monitoring a broad and wide area such as outside a home, business, or a parking lot, and you want to pickup as much of scene (field of view) as possible, you would select a wide angle 2.8mm or 3.6mm lens. Most fixed lenses come in a standard wide angle 3.6mm lens. This is a common and cost effective way to monitor an entire room or a broad area outside. If you are covering a wide area, room, or angle then a standared fixed lens (3.6mm) will be perfect and more cost effective.
What is varifocal lens and when should I use one?
A varifocal lens is kind of zoom lens where you have a range of focal lengths you can take. For example 3-8mm lens will allow you to adjust for the field of view you like (within that specified range). In essence, you have may lenses to choose from to get the perfect angle. Varifocal lenses cost more because you have the ability to self adjust the lens. If your camera is in the lobby and you want to watch the door or a cash register, you would use something like an adjustable varifocal lens. The higher the number, the smaller the field of view and there is a bigger zoom effect (objects become closer). So if you think you may want to "get closer" to an object, you may want to choose a varifocal lens to adjust so you can determine the exact angle and ideal width for your application.
Lens Focal |
Distance between video camera and the video subject area |
|||||||||||
5' away |
10' away |
15' away |
25' away |
50' away |
100' away |
|||||||
mm |
Horz area |
Vert area |
Horz area |
Vert area |
Horz area |
Vert area |
Horz area |
Vert area |
Horz area |
Vert area |
Horz area |
Vert area |
2.45 |
17.3' |
13' |
34.6' |
26' |
51.9' |
39' |
86.5' |
65' |
173' |
130' |
346' |
260' |
2.80 |
14' |
10.5' |
28' |
21' |
42' |
31.5' |
70' |
52.5' |
140' |
105' |
280' |
210' |
2.97 |
12.3' |
9.6' |
24.6' |
19.2' |
36.9' |
28.8' |
61.5' |
48' |
123' |
96' |
246' |
192' |
3.60 |
7.5' |
5.7' |
15' |
11.4' |
22.5' |
17.1' |
37.5' |
28.5' |
75' |
57' |
150' |
114' |
3.70 |
7.3' |
5.5' |
14.6' |
11' |
21.9' |
16.5' |
36.5' |
27.5' |
73' |
55' |
146' |
110' |
4.0 |
6.6' |
5' |
13.2' |
10' |
19.8' |
15' |
33' |
25' |
66' |
50' |
132' |
100' |
4.30 |
6.1' |
4.6' |
12.2' |
9.2' |
18.3' |
13.8' |
30.5' |
23' |
61' |
46' |
122' |
92' |
5.0 |
4.7' |
3.5' |
9.4' |
7' |
14.1' |
10.5' |
23.5' |
17.5' |
47' |
35' |
94' |
70' |
6.0 |
3.8' |
2.9' |
7.6' |
5.8' |
11.4' |
8.7' |
19' |
14.5' |
38' |
29' |
76' |
58' |
8.0 |
2.9' |
2.2' |
5.8' |
4.4' |
8.7' |
6.6' |
14.5' |
11' |
29' |
22' |
58' |
44' |
12.0 |
1.9' |
1.5' |
3.8' |
2.8' |
5.7' |
4.5' |
9.5' |
7.5' |
19' |
15' |
38' |
28' |
16.0 |
1.4' |
1.1' |
2.8' |
2.2' |
4.2' |
3.3' |
7' |
5.5' |
14' |
11' |
28' |
22' |
25.0 |
1' |
0.7' |
2' |
1.4' |
3' |
2.1' |
5' |
3.5' |
10' |
7' |
20' |
14' |
50.0 |
0.4' |
0.3' |
0.8' |
0.6' |
1.2' |
0.9' |
2' |
1.5' |
4' |
3' |
8' |
6' |
