1. The zoom levels

The Videology camera has a motor zoom and a motor focus. Since the camera is used here for measurement purposes the auto focus function has been switched off. Instead the appropriate focus position has been determined and saved for each zoom position.

the working distance between the camera lens and the object has been set precisely.

This can be made either with the aid of a measuring device, or the camera can be set to the greatest magnification (corresponds to level 10) and focussed on the object. This set-up ensures that all other zoom levels are also displayed in focus. The automatic focus setting must not be interpreted here as an auto focus!

The camera is therefore controlled as follows:

ten positions are factory-set around the zoom. The resulting image fields were selected so as to give a sensible overlapping of the image field sizes.

The focus is determined for each zoom position and then stored. If the camera was adjusted correctly all the positions will be shown in focus. This means that it is always necessary to refocus to the highest magnification, when objects of different heights are being measured.

2. The Parcentricity

In every zoom lens, optics are moved. This has always as a consequence that the centre of the image moves.

Example:

Crosshair is in the centre of the image

object is also centred at zoom level 1

Crosshair remains in the centre of the image but at zoom level 2 the object has moved away from the centre

In some applications this behaviour is not desired or permitted. In order to maintain a reference point, once established, in the zoom levels, the following solution has been programmed for the Videology camera:

Open the simple crosshair from the menu.

                                                                                       The crosshair can now be moved                                                                

Drag the crosshair back to the centre

Now click again on the saved zoom position of the object.

The position of the crosshair is set for the "fixed crosshair".

In this way the crosshair can be centred for all zoom positions, this means,the once specified point of centre remains.

It is a good idea to set the reference point at the greatest magnification and then adjust to this at all other zoom levels. In doing this, the camera should of course be mechanically aligned to this point in order to minimise deviations with reference to the camera.