WO2008078150A1

WO2008078150A1 - Calculating camera lens position information

Info

Publication number: WO2008078150A1
Application number: PCT/IB2006/055020
Authority: WO
Inventors: Mikko A. Ollila
Original assignee: Nokia Corporation
Priority date: 2006-12-22
Filing date: 2006-12-22
Publication date: 2008-07-03

Abstract

A temperature drift of a position sensor within a camera may be accounted for by a method comprising obtaining a sensor value indicative of a lens position of at least one lens of a camera, obtaining a temperature information related to the obtained sensor value, and calculating an actual lens position based on at least the sensor value and the temperature information.

Description

Calculating Camera Lens Position Information

TECHNICAL FIELD

The invention relates to calculating camera lens position information .

BACKGROUND

Digital cameras have been widely spread due to their easy and user friendly operation. Digital cameras may be understood as stand alone cameras or integrated cameras within electronic devices, such as, for example mobile phones, personal digital assistants (PDA) , mobile computers, laptops, MP3-Players, or any other kind of mobile multimedia device.

Users of digital cameras appreciate their capability to take sharp pictures without manually focusing of the image. Auto-focus is a mandatory feature in almost every digital camera. The auto-focus needs to position a lens such that the image is sharply imaged on the image sensor. Such digital image sensors may be understood as

CMOS-sensors or CCD-sensors, or any other sensors capable transforming a projected image into electronic information .

For providing auto-focus, cameras move the lenses between an infinity position and a macro position, depending on the distance between the elements of the image which shall be sharp in the image and the camera. The infinity position provides for sharp pictures of elements, which are far away from the camera, e.g. several meters to several hundred meters away from the camera. The macro position of the lens provides for sharp images of elements, which are close to the camera, e.g. several centimeters to several tens of centimeters.

For moving and positioning the lens during auto-focusing, a processor within the camera, which operates the auto- focus, needs to know the position of the lens. Without knowledge of the lens position, the processor is not able to correctly re-position the lens for auto-focusing. For calculating the position of the lens, each camera is calibrated with factory settings. For factory level calibration, the lens is moved to the mechanical end positions, e.g. the mechanical outermost positions of the lens, to which it can be moved. At these positions, sensor values indicative of the position are obtained.

For calibration purposes, the positions of the far and the near mechanical end positions of the lens, e.g. the sensor values of these positions, may be obtained and stored in memory. This measurement may be done after assembling the camera, i.e. at factory level. To allow further calibration, the lens may be moved to its macro position and its infinity position. When the lens is at the respective position and the sensor values may also be measured and stored in the memory.

During operation, the factory calibration is used to determine, at which actual position relative to the predetermined macro and infinity position the lens is positioned. From the knowledge of the sensor values at the mechanical end positions and the macro and infinity position, the processor which provides the auto-focus functionality may calculate the actual position from the actual sensor value. This may be done by calculating the offset of the actual sensor value from the sensor values obtained and stored during calibration. This position information may be used by the processor for providing re-positioning of the lens for auto-focus.

In other words, the position of the lens is calculated based on a difference between sensor values, which are obtained during calibration at factory level and at the moment, when the picture is to be taken.

However, this position calculation based on factory settings is subject to errors due to environmental influences to the sensor.

SUMMARY

In order to provide for a calculation of a lens position, which is independent of environmental influences, there is provided a method comprising obtaining a sensor value indicative of a lens position of at least one lens of a camera, obtaining a temperature information related to the obtained sensor value, and calculating an actual lens position based on at least the sensor value and the temperature information.

The position sensor may obtain information indicative of a position of the lens and may provide an electrical signal representing the position information.

The sensor value indicative of a lens position may be obtained using a photo reflector sensor. The photo reflector sensor may comprise a position sensor and a light source. The photo reflector sensor may measure a brightness value reflective from a reflective surface of the lens. The brightness may deviate with increasing distance from the light source, which may also be part of the photo reflector sensor, and the reflective surface of the lens. The light source may be a light emitting diode. For measuring the brightness value, the photo reflector sensor may comprise a photoactive transistor or any other kind of means, which is capable of measuring a brightness level. For measuring the sensor values of the position sensor, a hall sensor may also be used. For example, a hall sensor may be positioned at the lens, and a magnet may be positioned at a fixed position, or wise verser.

The output from the hall sensor may be amplified within a differential amplifier. Both offset and amplitude of the differential amplifier and the voltage supplied by the hall sensor to the amplifier may change as a function of temperature. In order to obtain temperature invariant position sensor results, it is necessary to take the temperature at the sensor into account.

Obtaining temperature information may result in obtaining information about the temperature of the position sensor. A sensor for measuring temperature information may be understood as temperature sensor. A temperature sensor may, for example, be integrated into the position sensor, i.e. the photo reflective sensor or the hall sensor. The temperature sensor may also, for example, be part of the light source. For example, the light source may be a light emitting diode. A voltage over the light source may, for example, be indicative of the temperature at the light source. This voltage may be used for measuring the temperature and obtaining temperature information.

The inventors found that there is a temperature drift at the position sensor. While at factory level, the mechanical end positions and the macro and infinity positions of the lens may be obtained at a certain temperature, the temperature during operation may differ. When using the camera in different environments or for a longer time, the temperature of the sensor may rise or fall relative to the temperature at which the calibration at factor level was done. It has been found that the position sensor may be subject to temperature drift, for which reason the inventors propose to use temperature information for calculating the actual lens position. When the position sensor changes its temperature, the infinity and macro positions, which can be calculated from the mechanical end positions, have shifted in relation to the calibration of these positions at factory level. This may falsify the calculation of the lens position. To account for this temperature drift, there is provided using temperature information together with position sensor values taken at the moment the picture is to be taken. With this additional information the temperature drift may be accounted for and the error in position calculation may be minimized.

By way of the provided method according to embodiments, the sensor value indicative of a lens position is obtained together with temperature information. Using this temperature information, the temperature drift of the sensor may be accounted for. The actual lens position may be calculated based on the position sensor value and the temperature information.

It has further been found that the temperature drift in many cases may be constant. This may result in a change of sensor values of the position sensor due to temperature changes being proportional to the temperature changes and do not deviate much overtime. In other words, sensors values taken at a certain lens position at a certain temperature will be time invariant. For this reason, it is proposed according to embodiments, to store a tuple of position sensor value and temperature information. Storing the position sensor value together with the temperature information may result in the possibility to re-use the already obtained sensor values and temperature information for further processing.

In case sensor values for a temperature obtained prior to taking a picture are already known, i.e. tuples of sensor values and temperature information are already stored in a memory, the re-use of these sensor values provides for faster auto-focusing. It is not necessary to drive the lens to the far mechanical ends to perform the repositioning of infinity and macro values. The re- positioning would considerably slow down the auto-focus lock-uptime to users. Once the sensor values for an actual temperature are known, the sensor values previously obtained can be re-used.

It is further preferred, to calculate a function of the temperature behavior of the position sensor from obtained sensor values. In this respect, it may be possible, to obtain position sensor values at defined positions, i.e. the far mechanical end positions, at different temperatures. From the acquired position sensor values at defined positions at different temperatures, it may be possible, to calculate a function defining the temperature behavior of the position sensor values. Therefore, it may be possible, to obtain from a few tuples of temperature values and position sensor values a function describing the relation between the position sensor value and the temperature. If this was the case, it would be possible to calculate a position sensor value at a temperature without measuring the position sensor value itself. In order to calculate an infinity position of the lens and a macro position of the lens, as well as the actual position of the lens, the position sensor values at the mechanical ends can be measured and the temperature information may be obtained at factory level. These reference values may be used for calibrating the camera. In order to re-use the calibration, it is proposed, according to embodiments, that the position sensor value is a reference sensor value indicative of a reference position of the lens. Using a reference position of the lens, it may be possible to calculate the actual position of the lens in relation to the reference position of the lens .

According to embodiments, the reference positions of the lens may be at least one of a far mechanical end position of the lens, or a near mechanical end position of the lens. Both positions may also be used together as reference positions of the lens. Based on these reference positions, the actual position of the lens may be calculated. The calibration of macro and infinity position relative to the reference positions may be done at factory level. When re-measuring the reference positions of the lens, a temperature drift of the position sensor may be accounted for and the calibration at factory level for obtaining the macro and infinity positions may be re-used. For example, the position sensor value at the reference position changes with changing temperature. When using this information about the drift of the position sensor value at the reference position, it may be possible to calculate the actual position from the position sensor values at the reference positions at the actual temperature. In order to calculate the actual position of the lens, embodiments provide calculating the actual lens position as a function of at least one of the stored reference position sensor value and the actual position sensor value. With one of the stored reference position sensor values and the actual position sensor value, the off-set between the sensor values may be obtained and from this and the calibration at factory level, the actual position of the lens may be calculated.

As has been described above, the position sensor is subject to temperature drift. In order to account for temperature changes, embodiments provide calculating the actual lens position as a function of one tuple of position sensor value and temperature information, and a tuple of the actual position sensor value, and the actual temperature information. Using the actual temperature information, a previously stored tuple of position sensor value and temperature information may be obtained, which may be suitable for the actual temperature. With this tuple being a reference, the actual sensor value may be evaluated and used for calculating the actual lens position .

In order to be able to select the correct tuple of stored position sensor value and temperature information, embodiments provide comparing the actual temperature information with the temperature information of a stored tuple. According to embodiments, the comparison may result in a similarity between the actual temperature information and temperature information of a stored tuple. If this is the case, i.e. the actual temperature deviates only to a amount, which is less than a threshold value, the position sensor value of the tuple of which the temperature information is similar to the actual temperature information, may be used for calculating the actual lens position. The position sensor value stored may be a reference position sensor value.

In case already obtained tuples of temperature value and position sensor value are available, and a function of the position sensor value depending on temperature has been calculated, it may also be possible to calculate from the obtained temperature the most probable position sensor value. Therefore, it is not necessary that at all temperatures, tuples of position sensor values, and temperature values are stored, but it may also be possible, to use already obtained temperature values to calculate a function of position sensor value in relation to temperature, and to calculate, in knowledge of a temperature, a most probable position sensor value.

Embodiments provide calculating the actual lens position as a function of one tuple of reference sensor value and temperature information related to the reference sensor value, which temperature information is at least similar to the actual temperature information. It has been found that reference sensor values together with temperature information may be stored in a memory. For different temperatures, the reference positions provide for different reference sensor values. These different reference sensor values may be stored in different tuples together with their respective temperature information. Over time, more and more different temperatures may be measured. At these different temperatures, reference sensor values may be obtained. Temperature and position information may be stored in a new tuple. Thus more and more tuples of temperature information and reference sensor values are stored. With the actual temperatures being similar to an already stored temperature, the corresponding reference sensor value may be used for calculating the actual lens position.

However, it may also happen that the actual temperature information differs from the temperature information stored in the tuples. In this case, i.e. in when the actual temperature differs more than a threshold value from the temperatures of the stored tuples, embodiments provide obtaining a new tuple of reference sensor value and new temperature information related to the obtained reference sensor value, and storing the new tuple. A database of different tuples with different temperatures may be built and re-used. The longer the camera is in operation, the less often it is necessary to obtain new tuples of reference sensor value and temperature information. The auto-focus process is getting faster with more tuples at different temperatures being stored.

According to embodiments, there is provided obtaining the sensor value from a photo reflector position sensor. For example, a photo reflector position sensor may comprise a light emitting diode and a photoactive transistor. A light emitting diode may emit light, which is reflected from a reflective surface being located at the lens. The reflected light may activate the photoactive transistor and depending on the amount of light being reflected, the current through the transistor may change. This current may be understood as a position sensor value.

It has further been found that the temperature information may be a voltage indicative of the actual temperature. For example, when using a light emitting diode, a hall sensor or any other semiconductor device within the position sensor, the voltage over this device may be used as information indicative of the temperature of the sensor.

It has further been found that the sensor values are subject to aging. For this reason, it may happen that the sensor values change over time even at temperatures, which are known. To account for this aging, embodiments provide obtaining and storing a new tuple of reference sensor value and temperature information related to the reference sensor value in intervals. The intervals may be chosen for example being months or years of lifetime of the position sensor. It may also be possible, to delete previously stored tuples at the end of each interval providing for creating new tuples of sensor values and temperature information after certain times. This provides for reducing the negative effect of aging of the sensor .

Using the obtained sensor value and temperature information, and calculating the actual lens position from the reference sensor values at a similar temperature allows for providing calculating the actual lens position for auto-focus. Auto-focus becomes independent from temperature drift of the photo reflective sensor.

Another aspect is a method comprising obtaining a reference sensor value indicative of a reference lens position of at least one lens of a camera, obtaining a temperature information related to the obtained reference sensor value, storing the reference sensor value and temperature information, obtaining an actual sensor value, obtaining an actual temperature information, comparing the obtained actual temperature information with stored temperature information, if there is no similarity, obtaining a new reference sensor value indicative of the reference lens position, obtaining a new temperature information related to the obtained new reference sensor value, storing the reference sensor value and temperature information, and calculating an actual lens position based on the stored reference sensor value and the temperature information, which temperature information is similar to the actual temperature information, and further based on the actual sensor value .

A further aspect is a module comprising a sensor for obtaining a sensor value indicative of a lens position of at least one lens of a camera, a temperature sensitive sensor for obtaining temperature information related to the obtained sensor value, and a processor for calculating an actual lens position based on at least the sensor value and the temperature information.

A further aspect is a camera device comprising such a module, further comprising a lens.

Another aspect is an electronic device comprising a previously described module. An electronic device may be understood, for example, as a mobile phone, a PDA, a module computer, a MP3-Player, or any other mobile entertainment device.

A further aspect is a computer program product in which a computer program code is stored in a computer readable medium, which computer program code realizes the method described above, when executed by a processor.

Another aspect is a computer program having a program code, which realizes the method described above, when executed by a processor. The processing components of the module and the electronic device can be implemented in hardware and/or software. It may be for instance a processor executing software program code for realizing the required functions. Alternatively, it could be for instance a circuit that is designed to realize the required functions, for instance implemented in a chipset or a chip, like an integrated circuit.

Moreover, a computer program product and a computer program are proposed, in which a computer program code is stored in a computer readable medium. When executed by a processor, the computer program code realizes the method proposed for the first considered aspect. This computer program product may be for instance a separate memory device or a component that is to be integrated in a larger device.

The invention is to be understood to cover such a computer program code also independently from a computer program product and a computer readable medium.

It is to be understood that all presented exemplary embodiments may also be used in any suitable combination.

Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not drawn to scale and that they are merely intended to conceptually illustrate the structures and procedures described herein.

BRIEF DESCRIPTION OF THE FIGURES

In the Figure shows:

Fig. 1 a camera with a lens according to embodiments; Fig. 2 a module for obtaining sensor values according to embodiments;

Fig. 3 a flowchart of a method according to embodiments; Fig. 4 a diagram showing temperature drift of sensor values;

Fig. 5 a diagram showing temperature drift of sensor values with a temperature drift during factory calibration .

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 illustrates a camera 2 with a camera body 4. The camera 2 comprises a display 6, a user interface processor 8, a memory 10, and a processor 12 for processing images. The processor 12 operates a CCD-chip 14, the lenses 16, 18, 20, and the module 22.

The processor 12 and the module 22 may be operated by a software program. The software program may be stored within the processor 12 and/or module 22 or may be loaded into the processor 12 and/or module 22. A data carrier 12a may store the program code and may be used to program the processor 12 and/or module 22. The program code of the software may operate the processor 12 and/or module 22 as will be described hereinafter. For auto-focusing, the processor 12 moves movable lens 18 between a macro position 24, and an infinity position 26. During auto-focusing stage, the lens 18 is moved in rough steps between fixed positions, and at these positions, the focus value is measured. From the measurement at the fixed positions, a focus curve is interpolated. Using the interpolated curve, a threshold value of a focus value is defined. The lens 18 is moved along the interpolated focus curve above the defined threshold. In this second step, the lens 18 is moved at finer steps to allocate the local maximum of the focus curve. To this end, the focus values obtained in the second step with the finer lens movement are interpolated and a maximum sharpness value is calculated. The lens 18 is then moved to the evaluated focus curve maximum. In order to move the lens 18 to the fixed positions during the first step with rough scanning and during the second step with fine scanning, the step sizes for moving the lens must be known beforehand. For this reason, the distance between the macro position 24 and the infinity position 26 of the movable lens 18 has to be known. From this distance, the step length for moving the movable lens 18 is calculated. Further, the lens 18 may be moved between the mechanical end positions 28, 30, which represent the outer most positions, to which the lens 18 may be mechanically moved.

Lens 18 comprises a reflective surface 32, which reflects light emitted from module 22. The operation of the camera 2 will be described further below.

Fig. 2 illustrates a module 22 comprising a photo reflector sensor 34, a measurement unit 36, a measurement unit 38, a processor 40, and a memory 42. The photo reflector sensor 34 comprises a light emitting diode 44, and a photo active transistor 46. Light emitting diode 44 or the light emitting diode 44 with the measurement unit 36 may be understood as temperature sensor. The photo active transistor 46 or the measurement unit 38 with the photo active transistor 46 may be understood as position sensor. Units 36, 38 may also be integrated within the photo reflector sensor 34. Instead of photo reflector sensor 34, a hall sensor for measuring the position of lens 18 may be used.

The light emitting diode 44 emits light, which is reflected by reflective surface 32, and measured by photo active transistor 46.

Measurement unit 36 measures the voltage over light emitting diode 44, which voltage is indicative of the temperature of the photo reflector sensor 34. This temperature may also be the temperature at the photo active transistor 46. The measurement unit 38 measures the current through the photo active transistor 46, which current is indicative of the amount of light reflected from reflective surface 32.

The operation of the photo reflector sensor 34 and the measurement units 36, 38 may be controlled by processor 40. The sensor values obtained from units 36, 38 may be processed by processor 40 and stored within memory 42. For example, within memory 42, position sensor values at reference positions together with temperature sensor values may be stored in tuples.

The operation of the camera 2 is illustrated in Fig. 3.

After assembly of the camera 2 it is calibrated (50) . The lens 18 is moved to the mechanical end position 28. At this mechanical end position 28, the module 22 operates as follows. The mechanical end positions 28, 30 may be understood as the positions to which lens 18 may be moved at the maximum, mechanically.

Light emitting diode 44 emits light to reflective surface 32, which light is reflected onto photo active transistor 46. At this moment, measurement unit 38 measures the current through photo active transistor 46, indicative of the amount of light reflected from reflective surface 32. As the distance between module 22 and reflective surface 32 influences the amount of light reaching the photo active transistor 46, the current measured by measurement unit 38 is indicative of the position of reflective surface 32, and thus lens 18. At the same time, measurement unit 36 measures the voltage over light emitting diode 44. The voltage measured over light emitting diode 44 is indicative of the temperature of photo reflector sensor 34.

Measurement unit 36 provides the processor 40 with the measured voltage, and measurement unit 38 provides the processor 40 with the measured current. This tuple is processed by processor 40 to memory 42 and stored in memory 42. During calibration (50), lens 18 is further moved to mechanical end position 30. At mechanical end position 30, module 22 again measures the current and voltage, which are indicative of the position of the lens and the temperature of module 22. These values are also stored in memory 42. Further, during calibration (50), lens 18 is moved by processor 12 to infinity position 26 and macro position 24 at which the current (position) and voltage (temperature) are also measured and stored. During calibration (50), the relation between the mechanical end positions 28, 30 and the macro and infinity positions 24, 26 are evaluated. From this relation, a function is created for calculating the position of the lens 18 from the measurement the position sensor and the temperature sensor, and for calculating the step sizes for autofocussing, as described above.

After calibration (50), the camera is shipped to users.

At startup (52), the measurement unit 36 measures the voltage over light emitting diode 44, which is indicative of the temperature of photo reflector sensor 34. The measured temperature information is compared with temperature information stored in one of a tuple stored in memory 42. If the measured actual temperature information matches with stored temperature information of a tuple in memory 42, the corresponding position sensor values are obtained from memory 42. This position sensor value is a position sensor value taken at a reference position of the lens 18 at the corresponding temperature .

With the position sensor values obtained at measurement unit 38, and the reference position sensor values loaded from memory 42, processor 40 calculates (54) the actual position of lens 18.

During operation of the camera, the module 22 may change is temperature due to device heating or ambient temperature. When the camera is activated (56), it is again checked, whether the temperature information obtained from measurement unit 36 matches with temperature information stored in memory 42. If this is not the case, processor 40 starts a new calibration (58) of lens 18.

For this reason, processor 12 moves lens 18 to the mechanical end positions 28, 30. At each of the respective positions 28, 30, module 22 obtains temperature information in measurement unit 36, and position sensor values in measurement unit 38. The tuples at the mechanical far ends are processed by processor 40 and stored to memory 42.

After this new calibration (58), lens 18 is moved into a position between macro position 24, and infinity position 26. Lens 18 is adjusted such that the image on CCD chip 14 is sharp. For calculating (60) the position of lens 18, processor 40 obtains from measurement unit 38 a sensor value 60. This sensor value is compared to the sensor values stored in memory 42 at the mechanical end positions 28, 30 at the actual temperature. Using the information about the sensor values at the mechanical end positions 28, 30 at the current temperature, processor 40 may calculate the actual position of lens 18. By taking the temperature into account, a temperature drift of module 22 may be accounted for.

With the calculated actual position of the lens, the auto-focus may be adjusted (62) .

When taking a new picture 56, processor 40 checks, whether within memory 42, tuples of position sensor values at the current temperature obtained in measurement unit 36 are available. If this is a case, the actual position of the lens 18 may be calculated (60) immediately from the stored tuples of sensor values. By obtaining new sensor values at different temperatures, memory 42 may build up a database of a plurality of tuples representing reference position information at different temperatures. Using these tuples, the processor 40 may calculate (60) the actual position of lens 18 without re-calibration (58).

To account for aging, during intervals, new sets of tuples may be obtained (64) . For this reason, memory 42 may be deleted and new tuples of measurements of measurement unit 36, and measurement unit 38 may be obtained at camera startup. After several operations of the camera, re-calibrations (58) have taken place and memory 42 is filled with new tuples, which account for the aging drift of the position sensor 34.

Fig. 4 illustrates the relation between temperature and position sensor measurements. The temperatures are measured within measurement unit 36, and the position sensor values are measured in measurement unit 38.

At factory level, the position sensor values 70a, 70b are obtained. These values 70a, 70b are obtained for the lens 18 being at the mechanical end positions 28, 30. Further, the lens 18 is moved to macro position 24 and infinity position 26. At macro position 24, the position sensor value 72a is obtained, and at infinity position 26 the position sensor value 72b is obtained. With these position sensor values 70, 72, it is possible to calculate the actual position of the lens 18. The calibration of the camera is done by calculating the distance between the position sensor values 70 at the mechanical end positions 28, 30, and the position sensor values 72 at infinity position 26 and macro position 24. During operation of the camera, module 22 may change its temperature. A changed temperature may cause the position sensor values to drift. In case a different temperature is detected, the lens 18 may again be moved to the outer mechanical end positions 28, 30. At the mechanical end position 30, the sensor value 74a is measured. At the mechanical end position 28, the sensor 74b is measured. The sensor values 74a, 74b are stored in memory 42 together with the temperature information measured in measurement unit 36. Using this newly calculated position sensor values at the changed temperature allows for calculating the macro and infinity position 76a, 76b. To calculate these positions in processor 40, the macro position 72a, and the infinity position 72b, together with the temperature drift obtained from the sensor values 74a, 74b are used.

In Figure 4, the curves 80a, 80b, 80c, 8Od are illustrated. Curve 80a illustrates the position sensor value in depence of the temperature at the mechanical end position 28. Curve 8Od illustrates the position sensor value depending on temperature at the mechanical end position 30. Curves 80b, and 80c illustrate the dependence of the position sensor value from the temperature at the macro (80b) and infinity (80c) positions. It has to be acknowledged that from a few tuples 70, 74, 78, the curves 80 may be described as functions of the position sensor value depending from the temperature. Using these functions, it may be possible to calculate any position sensor value at a given temperature. If curves 80 are defined by functions, it is not necessary to measure at each temperature a position sensor values at the mechanical ends 28, 30 and the macro and infinity positions 24, 26 and to store these for re- usage. It is rather possible to calculate the position sensor values at temperature values in between the measured temperature values from the functions.

When the temperature further rises, the lens 18 is again moved to the mechanical end positions 28, 30, and new sensor values 78a, 78b are obtained. The sensor values 78a, 78b together with the temperature are stored in memory 42.

Using the newly calculated sensor values at the mechanical end positions 28, 30, it is possible to calculate the actual position of the lens 18 and the macro position 24 and the infinity position 26 of the lens 18, even at different temperatures accounting for temperature drift of the position sensor 34.

Even a temperature drift during calibration at factory level may be accounted for. As illustrated in Fig. 5, at factory level, the temperature may change during the first calibration. The measurement of the sensor values is not done at a constant temperature. However, the temperature drift can be accounted for. In case the sensor values at the mechanical end positions 28, 30 as well as the macro and infinity positions 24, 26 are obtained with a temperature drift during factory calibration, it is possible, to calculate the correct sensor values 70a, 70b, 72a, 72b later on. For example, when during operation the function between temperature and position sensor value is obtained, and the curves 80 can be calculated from already obtained position sensor values 74, 78, the correct position sensor values at factory level 70, 72 can be obtained using the functions 80. The functions illustrated by the processors 12, 22 executing software or the functions illustrated by the position sensor 34 can also be viewed as means for obtaining camera lens position.

While there have been shown and described and pointed out fundamental novel features of the invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices and methods described may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

What is claimed is:

1. A method comprising: obtaining a sensor value indicative of a lens position of at least one lens of a camera; obtaining a temperature information related to the obtained sensor value; and calculating an actual lens position based on at least the sensor value and the temperature information .

2. The method of claim 1, further comprising storing a tuple of sensor value and temperature information.

3. The method of claim 1 or 2, wherein the sensor value indicative of the lens position is a reference sensor value indicative of a reference position of the lens.

4. The method of claim 3, wherein the reference position of the lens is at least one of:

A) a far mechanical end position of the lens;

B) a near mechanical end position of the lens.

5. The method of claim 3, further comprising calculating the actual lens position as a function of at least one of the stored reference sensor value and the actual sensor value.

6. The method of claim 5, further comprising calculating the actual lens position as a function of one tuple of sensor value and temperature information, and the actual sensor value, and the actual temperature information .

7. The method of any one of claims 1 to 6, further comprising comparing the actual temperature information with the temperature information of a stored tuple.

8. The method of claim 6 or 7, further comprising calculating the actual lens position as a function of one tuple of reference sensor value and temperature information related to the reference sensor value, which temperature information is at least similar to the actual temperature information.

9. The method of claim 7, further comprising obtaining a new tuple of reference sensor value and a new temperature information related to the obtained reference sensor value, and storing the new tuple, if the actual temperature does not correspond to a stored temperature information of a stored tuple.

10. The method of any one of claims 1 to 9, wherein obtaining the sensor value comprises obtaining a value of a photo reflector based position sensor.

11. The method of any one of claims 1 to 10, wherein obtaining the temperature information comprises obtaining a voltage indicative of a temperature.

12. The method of any one of claims 1 to 11, wherein obtaining the temperature information comprises measuring a voltage at a light source of a photo reflector based position sensor.

13. The method of any one of claims 1 to 12, further comprising obtaining and storing a new tuple of reference sensor value and temperature information related to the reference sensor value in intervals.

14. The method of any one of claims 1 to 13, further comprising adjusting an auto-focus using the calculated actual lens position.

15. The method of any one of claims 1 to 14, further comprising calibrating the sensor values of a macro lens position and/or an infinity lens position from the reference sensor value.

16. The method of any one of claims 1 to 15, further comprising storing more than one tuple of reference sensor value and temperature information.

17. A method comprising: obtaining a reference sensor value indicative of a reference lens position of at least one lens of a camera; obtaining a temperature information related to the obtained reference sensor value; storing the sensor value and temperature information; obtaining an actual sensor value; obtaining an actual temperature information; comparing the obtained actual temperature information with stored temperature information; if there is no similarity; obtaining a new reference sensor value indicative of a reference lens position; obtaining a new temperature information related to the obtained new reference sensor value; storing the reference sensor value and temperature information; and calculating an actual lens position based on a stored tuple of the sensor value and the temperature information, which temperature information is similar to the actual temperature information, and based on the actual sensor value.

18. A module comprising: a sensor for obtaining a sensor value indicative of a lens position of at least one lens of a camera; a temperature sensitive sensor for obtaining temperature information related to the obtained sensor value; and a processor for calculating an actual lens position based on at least the sensor value and the temperature information.

19. The module of claim 18, further comprising a memory for storing the tuple of sensor value and temperature information .

20. The module of claim 18 or 19, wherein the sensor is arranged for measuring sensor values at least one reference position of the lens.

21. The module of claim 20, wherein the reference position of the lens is at least one of:

A) a far mechanical end position of the lens;

B) a near mechanical end position of the lens.

22. The module of claim 18, wherein the processor is arranged for calculating the actual lens position as a function of one tuple of reference sensor value and temperature information, and the actual sensor value, and the actual temperature information.

23. The module of any one of claims 18 to 22, wherein the processor is arranged for comparing the actual temperature information with the temperature information of a stored tuple.

24. The module of any one of claims 18 to 23, wherein the sensor is a photo reflector based position sensor.

25. The module of any one of claims 18 to 24, wherein the temperature sensor is arranged for obtaining a voltage over a passive semiconductor element.

26. The module of any one of claims 18 to 25, wherein the module is arranged for providing the calculated lens position to an auto-focus unit.

27. A camera device comprising a module of claim 18, further comprising the lens.

28. An electronic device comprising: a module according to claim 18.

29. A computer program product in which a computer program code is stored in a computer readable medium, which computer program code realizes the method of claim 1 when executed by a processor.

30. A computer program having program code, which realizes the method of claim 1 when executed by a processor.