ICameraControl::get_FocalLengths method (vidcap.h)

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The get_FocalLengths method returns the focal lengths of the camera lenses.

Syntax

HRESULT get_FocalLengths(
  [out] long *plOcularFocalLength,
  [out] long *plObjectiveFocalLengthMin,
  [out] long *plObjectiveFocalLengthMax
);

Parameters

[out] plOcularFocalLength

Receives the ocular focal length.

[out] plObjectiveFocalLengthMin

Receives the minimum objective focal length.

[out] plObjectiveFocalLengthMax

Receives the maximum objective focal length.

Return value

Returns an HRESULT value.

Remarks

In a two-lens camera, the objective lens is closer to the subject, and the ocular lens is closer to the camera. The ocular focal length is fixed. If the camera has an optical zoom, the objective focal length can vary within a fixed range. Magnification is calculated as the ratio of objective/ocular focal length. Because the magnification is expressed as a ratio, it has no units. Therefore, the units for the focal length are not defined by this interface.

If the camera supports optical zooming, the current zoom level is expressed as integer values between a range Zmin and Zmax. The objective focal length can then be calculated as follows:

Lcur = ( ( (Zcur - Zmin) * (Lmax - Lmin) ) / (Zmax - Zmin) ) + Lmin

where:

• Lcur = Current objective focal length.
• Lmin, Lmax = Minimum and maximum objective focal length.
• Zcur = Current zoom setting. See ICameraControl::get_Zoom.
• Zmin, Zmax = Minimum and maximum zoom setting. See ICameraControl::getRange_Zoom.

Lcur

, you can calculate the magnification.

Requirements

See also

Error and Success Codes

ICameraControl Interface