List / Range of lens focal lengths

Using the List/Range and the List of Resolutions, you can set complex dependences of view angles on the aspect ratio, resolution and the lens focal length of a camera model.

In the List/Range box of the Sensor and Lens panel, you can specify a list of focal lengths of possible lenses of the camera or a range of focal lengths.

If a list of focal lengths is specified, then only values from the list will be present in the drop-down list of the Lens focal length combobox. You will be able to set focal length out of the list, but with value out of the list, the comboboxes turn pink.

If a focal length range is specified, then only values within the range will be present in the drop-down list of the Lens focal length combobox. Changing focal length is allowed only within the specified range.

It is possible to set real angles of view for each value of the focal length in the list or for min and max values of the range. If the real angles of view are set, then when all the other parameters coincide, the lens distortion modeling is automatically turned on.

You can set the aperture (F-number) for each lens.

If the List / Range and List of Resolutions strings are specified in the camera model parameters, the user only needs to select the lens focal length and resolution from the drop-down lists to obtain accurate model of camera's view area, taking into account lens distortion and dependence of active area size of the image sensor from the resolution.

The List / Range string can be in any of the following formats:

F1; F2; F3.. list of focal lengths in millimeters separated by a semicolon.

Example: 2.8;4;12;18

Fmin - Fmax. Minimum and maximum focal lengths divided by dash.

Example: 4-6

Ar – is the Aspect ratio of the active area of the image sensor. If the ratio is 4:3, then it can be omitted.

Cr – Crop. If Crop = 1, then it can be omitted.

Fmin, Fmax – the minimum and maximum focal lengths.

Ahmin, Avmin, Admin – horizontal, vertical and diagonal angles of view with minimum focal length.

Ahmax, Avmax, Admax – horizontal, vertical and diagonal angles of view with maximum focal length.

Dmax - maximum aperture (minimum F number at minimum focal length). Can be omitted.

Dmin - minimum aperture (maximum F number at maximum focal length). Can be omitted.

To simulate lens distortion, you must specify at last one of three angles of view (horizontal vertical or diagonal). It is better to specify two angles if two angles are known. For minimum and maximum focal lengths the same type of angles should be specified.

If aperture is specified, then when choosing a focal length from the specified range, the specified aperture will be assigned to the lens of the active camera in the Sensitivity and resolution box.

If the Latin letter "S" is set as the first character in the List/range of focal lengths, then the distortion will be simulated in simplified way. If the Latin letter "A" is set as the first character in the List/range of focal lengths, then the lens distortion modeling method (accurate or simplified) will be selected automatically depending on the source data. It is recommended to set the letter "A" in most cases.

The Lens Distortion simulation is automatically turned on when the active camera has Crop coincides with Cr, and the focal length is in the range Fmin..Fmax.

If the active camera's Aspect ratio does not match Ar, then VideoCAD will still try to simulate distortion, but the modeling accuracy will be worse.

At the boundaries of the range, the accuracy of the simulation is determined only by the initial values, but within the range the actual distortion may differ.

You can enter several non-overlapping ranges of focal lengths or several identical/overlapping ranges of focal lengths, but with different Aspect ratios or crops.

Ar1|Cr1|F1|Ah1|Av1|Ad1FD1; Ar2|Cr2|F2|Ah2|Av2|Ad2FD1; Arn|Crn|Fn|Ahn|Avn|AdnFDn;… A list of substrings separated by semicolons.

Each substring consists of the values:

Arn – is the Aspect ratio of the active area of the image sensor. If the ratio is 4:3, then it can be omitted..

Crn –Crop. If Crop = 1, then it can be omitted.

Fn – lens focal length.

Ahn, Avn, Adn – horizontal, vertical and diagonal angles of view with focal length = Fn.

Dn - aperture (F number) at focal length Fn. Can be omitted.

To simulate lens distortion, you must specify at last one of three angles of view (horizontal vertical or diagonal). It is better to specify two angles if two angles are known. For each focal lengths the same type of angles should be specified.

If aperture is specified, then when choosing a focal length from the specified range, the specified aperture will be assigned to the lens of the active camera in the Sensitivity and resolution box.

The Lens Distortion simulation is automatically turned on when the active camera has Crop coincides with Cr, and the focal length equals one of Fn values in the list.

If the active camera's Aspect ratio does not match Ar, then VideoCAD will still try to simulate distortion, but the modeling accuracy will be worse.

The list of focal lengths taking into account lens distortion can contain substrings that activate the FishEye camera modeling mode and specify the FishEye camera view angles. Thus, one camera can be modeled as a camera with lens distortion and as a FishEye camera depending on the chosen focal length, resolution and crop.

EAr1|Cr1|F1|Ah1|Av1|Ac1FD1;

Each FishEye substring consists of the values:

E – substrings start with the letter E - so the substring contains the angles of the field of view for FishEye camera.

Arn – is the Aspect ratio of the active area of the image sensor. If the ratio is 4:3, then it can be omitted.

Crn – Crop. If Crop = 1, then it can be omitted.

Fn – lens focal length.

Ahn, Avn, Acn – horizontal, vertical and circular view angles with focal length = Fn.

Dn - aperture (F number) at focal length Fn. Can be omitted.

If aperture is specified, then when choosing a focal length from the specified range, the specified aperture will be assigned to the lens of the active camera in the Sensitivity and resolution box.

If an active camera has the Aspect ratio equal Arn, Crop equal to Cr and focal length is equal to Fn, then the active camera will become FishEye and the horizontal, vertical and circular angles will be assigned to the corresponding view angles on the PTZ or Fisheye panel.

The List / Range string can be no more than 200 characters.

The List / Range string is included in the list of camera model parameters and can be automatically assigned to the active camera when it is assigned a model from the Table of Camera Models.

The List / Range string can be edited as plain text or using the drop-down form, which can be opened by the button in the upper corner of the List / Range box.

On the form, select the required tab: List, Range, List with distortion or Range with distortion.

In the Modeling distortion combo box, choose how to simulate lens distortion.

•	Do not simulate - do not simulate lens distortion. The camera model will use view angles calculated from the lens focal length and the size of active area of the Image sensor.

•	Simulate Accurately - Accurately simulate lens distortion. In case of inaccurate initial data, the picture may be distorted. Displaying dozens of cameras with distortion on the screen at the same time can lead to delays.

•

Simulate Simplistically - just assign vertical and horizontal actual view angles to the model, regardless of the lens focal length and the size of the active area of the image sensor. An undistorted picture will be obtained regardless of the accuracy of the angle values. The accuracy of the simulation depends on the accuracy of the angles, but in any case it is worse than with the exact simulation of lens distortion. Simplified distortion modeling requires much less resources to redraw the screen in 2D and 3D.

•	Autoselect - choose the method of modeling lens distortion automatically depending on the input data.

•	FishEye (on the List with Distortion tab only) - - the entered Real view angles will be assigned to the corresponding view angles on the PTZ or Fisheye panel if the Aspect Ratio, Crop and Focal Length match the corresponding parameters of the active camera.

Then select or enter the required values in the boxes and click Add. The string will be automatically formed in the top box of the form.

Unknown angle values can be omitted. The Aperture (F-number) boxes can also be left blank.

To record the string to the List / Range box, click Record.

Clear clears the top box of the form.

Cancel closes the form without recording the string.

To control possible errors, while entering angle values, the Aspect ratios are displayed:

•	of active area of the image sensor set for this lens (Sens:) and

•	calculated from the entered view angles (Ang:).

If the calculated values are outside the normal limits, the aspect ratios are colored red. This is not necessarily an error, but you should carefully check the values entered on the form. It is possible that the entered view angles do not correspond to the entered Aspect ratio of the active area of the image sensor.

If the form is called from the Table of Camera Models, then the Set default button is added to copy the current lens parameters to the parameters of the model edited in the Table as the default lens.

You can see a lot of examples of the List/Range at real camera models in the Table of camera models.

Help URL: http://www.cctvcad.com/videocad_help/index.html?listorrange.htm