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Focal length is calculated
Name:admin  time2011.09.27  Read:

Focal length is calculated
A formula for calculation: The calculation of field of view and focal length field of view means the size of the object is ingested, the size of the field of view is to be ingested object distance lens, lens focal imaging head and the required size determined.
1, the lens focal length, field size, and the lens to the object is taken up is calculated as the distance;
f = wL/W 2, f = hL/h
f; lens focal length w: width of the image (the subject is in ccd imaging target surface width)
W: width of the subject
L: the distance from the subject to the lens
h: height of the image (the subject is in ccd imaging target surface height) Field (uptake scene) height
H: height of the subject is
ccd target surface Dimensions Unit: mm
Specification
1/3 "
1/2 "
2/3 "
1 "
W
4.8
6.4
8.8
12.7
H
3.6
4.8
6.6
9.6
Since the width and height of the camera image of the television receiver picture width and height, as are the ratio of 4:3, the same as L, H, or W increases, f becomes smaller, the same as H or W, L increases When, f increases.
2 FOV calculation if you know the horizontal or vertical viewing angle can be calculated according to the formula field width and height. Horizontal angle β (horizontal viewing angle) β = 2tg-1 = vertical field angle q (vertical viewing angle) q = 2tg-1 = where w, H, f above horizontal field angle and vertical field angle relationship is as follows: q = or = q Table 2 lists the different sizes of different focal length f of the imaging layers and the horizontal field angle of the b value, if you know the horizontal or the vertical field angle can be calculated as Field of the field can be calculated as the height H, and field width W. H = 2Ltg, W = 2Ltg example; camera pickup tube 17mm (2/3in), the lens focal length f is 12mm, from Table 2 Richard horizontal field angle of 40 ℃ and the camera lens and the distance to the object ingestion 2m, Find the width of the field of view w. W = 2Ltg = 2 × 2tg = 1.46m then H = W = × 1.46 = 1.059m more and longer focal length f, the smaller the field of view, surveillance objectives are smaller.
As graphically shown by the camera lens field of view wide (W). High (H) and the distance from the camera (L) decision, once the decision of the camera to monitor the scene, the correct choice of lens focal length on the origin of three factors; *. Want to monitor the size of the scene * The camera distance to the subject * The camera imager ruler who: 1/3 ", 1/2", 2/3 "or 1." Graphic Select Lens steps: The desired field of view and focal length of the lens there is a simple relationship. Using this relation can choose the appropriate lens. Estimation or measurement of the maximum width of the field; estimation or measurement of the camera and the real distance between the scene being shot; with 1/3 "lens used in Figure 2, using a 1/2 lens used in Figure 3, using a 2/3" lens Using Figure 4, using a lens used in Figure 5. Specific methods: in the W and L is the axis of Figure 2-5, the identified focal length of the lens should be used. To ensure the scene being completely contained in the visual field, the intersection coordinates should be used, the value indicated by the line side. For example: a wide field of view 50m, distance 40m, with 1/3 "format lens, the intersection of the coordinate graph represents 4mm lens than a point on the line side, which means that if you can not use the 4mm lens field of view covering 50m, while with 2.8mm lens visual field can be completely covered.
f = vD / V or f = hD / H
Where, f is focal length, v represents the vertical height of the CCD target surface, V represents the observed object height, h represents the horizontal width of the CCD target surface, H represents the width of the object being observed.
Example: Assuming a 1/2 "CCD camera observations, the measured object width 440 mm, height 330 mm, 2500 mm lens focal distance objects. Can be calculated by the formula:
Focal Length f = 6.4X2500/440 ≈ 36 mm or focal length f = 4.8X2500/330 ≈ 36
毫米
When the focal length figures are calculated, if there is no corresponding focal length of the lens is normal, then according to the product catalog select a similar model, generally choose smaller than the calculated value, so perspective will be larger.
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