VideoCAD

Sensitivity and Resolution

 Lens

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Sensitivity and Resolution

 Lens

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Sensitivity and Resolution

 Lens

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Iris type

Fixed Iris

Manual Iris

Auto Iris

DC

Video Drive

-Level+

ALC

 

Boxes:

 

Aperture limits (F-number)

Curr. aperture (F-number)

Min. illum.

 

Resol. (lp/mm)

 


Iris type

Fixed Iris

 

Fixed Iris. Aperture value is specified in the left box of Aperture limits. During modeling the aperture does not vary.

 

Manual Iris

 

Manual iris. Aperture can be changed manually within specified limits, in the Curr. aperture box. Aperture limits are specified in the Aperture limits boxes.

During modeling the Aperture does not automatically vary.

 

Auto Iris

 

Automatic iris. During modeling the aperture automatically varies depending on scene illumination. Aperture change limits are specified in the Aperture limits boxes.

Current value of the Aperture during modeling is displayed in the Curr. aperture box.

If the automatic iris is chosen, AESC (electronic shutter) in camera parameters is switch off, adaptation to the illumination is performed only by changing aperture.

 

Auto Iris can be of two types:

Auto Iris > DC

 

The iris control signal, which comes from camera to the lens, is a direct-current voltage. DC signal is produced by camera depending on image sensor illumination. BLC (back light compensation) can work with DC iris lens. Image contrast can be adjusted by AutoIris DC -Level+ adjuster on camera's case.

 

Not all cameras have the circuit for controlling DC lens.

 

Auto Iris > Video Drive

 

The iris control signal, which comes from camera to the lens, is a video signal. This video signal will be transformed to iris control voltage by an internal circuit, which is in the lens. BLC can not work with Video iris lens, as a rule. Image contrast can be adjusted by -Level + screw on lens case.

 

On Video Drive lens there are screws:

Auto Iris > Video Drive > -Level+

 

Adjuster of iris sensitivity to video signal. Visually this adjuster changes image contrast which is obtained as a result of auto iris adjustment. If the contrast is too high, bright areas on the image are white level clipped.

 

Adjustment range of real cameras can be different.

 

Auto Iris > Video Drive > ALC

 

Sensitivity to peaks or to average level of video signal.

If the slider is closer to Peak, the image contrast is adjusted by the brightest spots of the image even if they occupy insignificant square. In this case bright areas are seen well, but dark areas can be black level clipped and not be displayed.

 

If the slider is closer to Average, the image contrast is adjusted by an average level of image brightness. At that the brightest areas on the image, which occupy small square, can be white level clipped and not be displayed.

Optimum position of this adjuster depends on scene features.

 

Adjustment range of real lenses can be different.

 

Boxes:

Aperture limits (F-number)

 

In the left box the maximum aperture value (F-number), which the lens can have (fully opened aperture), is entered.

In the right box the minimum aperture value (fully closed aperture) is entered.

 

The more the F-number is, the less light passes through the lens.

 

These values are given in the lens specification.

For Fixed Iris lenses the fixed aperture (F-number) is entered in the left box.

 

Curr. aperture (F-number)

 

Current aperture value.

 

For Manual Iris lenses in this box it is possible to change aperture value.

 

For Auto Iris lenses in this box the aperture value calculated during modeling is displayed.

 

In the project 2 values are stored: for day time and night time.

 

This value can be automatically used at calculation and modeling of depth-of-field.

 

If the Auto Iris Control operates and closes the aperture, the box becomes aqua color.

 

If the Current aperture reaches limit value, the box becomes yellow together with box in which the limit value is set.

 

If in the box an aperture value, exceeding maximum aperture value, is entered manually, the box becomes red together with box in which the maximum aperture value is set.

 

Min. illum.

 

In the box the calculated value of minimum scene illumination at fully opened aperture is displayed.

 

This parameter is for information only.

 

Resol.(lp/mm)

 

Resolution of the lens in line pairs per millimeter (lp / mm).

Lp / mm - is the number of pairs of lines (black + white line) perpendicularly intersecting a segment on the image sensor of length of 1 millimeter.

Note the difference with the unit of camera resolution, LPH. Resolution of cameras is measured in the amount of black and white lines, but the lens resolution is measured in line pairs , that is, at the same actual resolution, the lp / mm value is in 2 times less than LPH.

 

Effect of lens resolution on the final resolution of the camera depends on the ratio of lens resolution in lp / mm to the number of pixels on the image sensor per 1mm (pixel density on the sensor) . Thus, the smaller the size of the image sensor is and the more pixels on it - the higher lens resolution must be in order that the lens does not spoil the resolution of the camera .

 

At the top box you can specify the number of line pairs per millimeter (lp / mm), and in the box below ( % contrast ) you should enter contrast drop in % according to MTF (Modulation Transfer Function) at the specified value of lp / mm.

 

In the 3D Video window image resolution will be limited by values in these boxed. If N/A is chosen, then the lens resolution limitation is disabled.

You can also simulate the camera resolution. When the lens resolution simulation and camera resolution simulation are both enabled, then their effects are summarized.

 

You can check resolution visually using the Test chart.