Focusing of optical devices

The present subject matter includes a method of focusing of an optical imaging apparatus. The method comprises causing illumination of an object using an illuminating beam to thereby cause generation of a scattered beam. A first set of luminous parameters are derived from a first detected position of a luminous representation formed by the scattered beam from the object. The illumination-beam is focused upon the object by triggering a movement of the object along an optical-axis in a first direction, the first direction being based a numerical-representation of the first set of luminous parameters. A second set of luminous parameters are derived from a second detected position of the luminous-representation of the object, the second detected position being related to the first detected position and the movement of the object. The focusing of the illumination beam is ceased based at-least on a numerical-representation of the second set of luminous parameters.

FIELD

The present subject matter relates to focusing of optical-devices.

BACKGROUND

An imaging digital microscope employing an infinity corrected microscope objective lens usually produces a blurred image when the object is placed outside the focal plane of the objective lens. In order to produce a sharp image, one can vary the distance between the object and objective lens until the desired sharp image is produced.

A lot of existing algorithms enabling automation of such a procedure involve optimization of a predefined merit-function, with respect to an image recorded by an array-detector of the microscope, as based on the distance between the object and the detector. Such methods depend on formation of a distinguishable image and prove effective only over an extremely limited range in the close proximity of the optimal position. When the object is placed far away from the focal plane (at the distance much larger than the depth of focus distance from the focal plane of the objective), the image is blurred so much that the merit functions (or focus functions) used for focusing vary so slowly that it is difficult to detect whether the distance between the object and the objective lens should be increased or decreased in order to achieve focusing. In practical implementation, the changes of focus function when far away from the focal plane may become buried in measurement noise.

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified format that are further described in the detailed description of the present disclosure. This summary is neither intended to identify key or essential inventive concepts of the disclosure, nor is it intended for determining the scope of the invention or disclosure.

In an embodiment, the present subject matter refers to a method for focusing of an optical imaging apparatus. The method comprises causing illumination of an object using an off-axis illuminating beam to thereby cause generation of a scattered beam. A first set of luminous parameters are derived from a first detected position of a luminous-representation formed by the scattered beam from the object. The illumination-beam is focused upon the object by triggering a movement of the object along an optical-axis in a first direction, the first direction being based on a numerical—representation of the first set of luminous parameters. A second set of luminous parameters are derived from a second detected position of the luminous-representation of the object, wherein the second detected position is related to the first detected position and the movement of the object. Thereafter, the focusing of the illumination beam is ceased based at-least on a numerical-representation of the second set of luminous parameters.

In accordance with an implementation of the embodiment, the focusing of the off-axis illumination-beam is done upon the object through triggering movement of the object along the optical-axis in the first direction, after having derived the first-set of luminous parameters and before deriving the second set of luminous parameters.

In another embodiment, the present subject matter refers to a method of auto-focusing of an optical-imaging apparatus. The method comprises causing illumination of an object using an off-axis illuminating beam to thereby cause generation of a scattered-beam. A set of luminous parameters is derived from a detected position of a luminous-representation formed by the scattered-beam from the object. An auto-focusing operation is performed by triggering movement of the object along an optical-axis in a pre-determined direction, wherein the direction is dependent at-least upon a position-attribute within the set of parameters.

In another embodiment, the present subject matter refers to an optical imaging apparatus comprising an objective-lens configured to project an off-axis illuminating-beam upon an object to thereby cause generation of a scattered beam. An array detector is configured to form a luminous-representation of the object based on the scattered beam from the object. A processing system is configured to derive a first set and a second set of luminous parameters from a first and second detected position of the luminous-representation, respectively, and thereafter determine at least a numerical-representation based upon each derived set of parameters. An actuator is triggered by the processing system upon derivation of the first set of luminous parameters and prior to derivation of the second set of luminous parameters, wherein said linear—actuator is further configured to execute movement of the object along an optical-axis in a first direction defined by the numerical-representation of the first set of parameters to thereby enable focusing of the illumination-beam upon the object. The-actuator is further triggered by the processing system upon derivation of the second set of parameters and determination of the numerical-representation, such that the actuator is now configured to cease the focusing of the illumination beam upon the object.

Overall, the present subject matter facilitates an enhanced focusing with respect to the optical-systems such as microscopic-devices. More specifically, the present subject matter aims at rendering the focusing efficient enough to cover the objects lying far away from the focal plane, i.e. at the distance much larger than the depth of focus. Such efficiency is at-least achieved by virtue of detection of a precise direction in which the object is moved to approach the focal plane during focusing.

To further clarify advantages and features of the invention claimed herein, example descriptions and embodiments are rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only example embodiments of the invention and are therefore not to be considered limiting of its scope. The disclosure will be described and explained with additional specificity and detail with the accompanying drawings.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the present disclosure is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the present disclosure as illustrated therein being contemplated as would normally occur to one skilled in the art to which the present disclosure relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the present disclosure and are not intended to be restrictive thereof.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this present disclosure belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

As shown in the figure,FIGS. 1aand 1billustrates a method of focusing an optical imaging apparatus.

ReferringFIG. 1a, the method comprises causing illumination (step102) of an object using an off-axis illuminating-beam to thereby cause generation of a scattered beam. The illumination of the object is triggered by selectively rotating a frame comprising an off-axis aperture in a first position and a diffuser in a second position to interchangeably place the aperture and the diffuser in position with respect to an optical-beam, e.g., a collimated-beam for generating the illuminating-beam. The illumination of the object is caused by transmitting the off-axis illuminating-beam from a source via a beam-splitter to an objective-lens; and thereby focusing the transmitted beam upon the object via the objective lens. Thereafter, in the second position, the illumination of the object is caused by the diffused beam.

Taking into account the aforesaid first position, a first set of luminous parameters are derived (step104) from a first position of the scattered rays when they impinge an array detector. The parameters are derived from a luminous-representation or a light-spot obtained by projection of the scattered beam from the object upon the array-detector.

As explained later, a second set of luminous parameters may be further optionally derived from a second-detected position of the luminous representation of the object, the second-detected position being related to the first-detected position and the movement of the object. The luminous representation in the second position may correspond to either an image or may still correspond to the light spot, based on whether the object is in-focus or out of focus.

In one implementation, each of the first and second set of luminous parameters correspond to a ratio of (A−B) and (A+B) with respect to each of the first and second detected positions of the luminous-representation. ‘A’ represents an instantaneous power of the scattered-beam detected by one half of an array detector arranged to render the luminous-representation based on the scattered beam. On the other hand, B represents an instantaneous power of the scattered beam detected by the other half of the array detector. In another implementation, each of the first and second set of parameters represents coordinates of a centroid of a light spot formed by projection of the scattered beam upon the array-detector that is arranged to render the luminous-representation. Hereinafter, such centroid of light-spot has been referred as a ‘center of mass’.

In an example, the elements A and B denotes luminance (i.e. luminous intensity per unit area) with respect to the light-spot as detected within the respective halves of the array-detector. Accordingly, each of the first and the second set of parameters denotes ratio of: a) difference between luminance of the light-spot as detected by the two halves of the array-detector, to the b) sum of luminance with respect to said two halves. In another implementation, wherein centroid of the light-spot is acting as an element, each of the first and the second set of parameters represent positions of the light-spot within the array-detector. Further, an axis separating the two-halves of the array-detector may be configured to represent an optical-axis of the optical-imaging apparatus.

After the derivation of the first set of parameters, a movement of the object is triggered along an optical-axis in a first direction for focusing (step106) the illumination beam upon the object. The movement may involve moving the object itself relative to the objective lens or moving the objective lens relative to the object. Such first-direction corresponds to a direction towards the focal-plane of the optical-imaging apparatus along the optical-axis and is based on a numerical-representation of the first set of luminous parameters. The numerical-representation in-turn corresponds to representation through a unique arithmetic-sign associated with respect to a corresponding numeric-value, the sign being awarded in reference to a location within a coordinate-system associated with the array-detector.

Upon occurrence of said movement, the light-spot as rendered by the array-detector also undergoes a change in location. Due to such location change, the light spot may either remain within a particular half of the array-detector or may begin to be partially rendered in the other-half as well. In respect of the implementation based on detection of luminance, the first-set of parameters remain non-variable as along as the light spot remains rendered within one half of the array detector. The first set of parameters undergoes a change as and when light-spot begins to be at least partially-rendered by other half as well. However, in respect of other implementation based on detection of centroid or light spot, the movement of the object immediately leads to change in position-coordinate of the light-spot within the array-detector, i.e. an immediate-change is recorded within the first set of parameters.

Further, the focusing of the illumination beam is ceased (step108) in case the movement imparted along the optical-axis in step106leads to arrival of the object at a designated location substantially closer to the focal-plane. Such arrival at the designation location corresponds to a position at the central-axis of the array-detector, wherein both A and B turn equivalent to each other i.e. A=B. At this moment, the currently determined luminous parameters neither exhibit a numerical value, nor any numerical representation which corresponds to any numerical sign. In other words, the currently determined set of luminous parameters corresponds to a NULL value. In case of centroid of the light-spot is taken into consideration with respect to said NULL position, the same is observed as positioned within the central-axis of the array-detector.

In another implementation, the motion as imparted to the object in step106results in a scenario where the numerical representation of the currently determined set of luminous parameters turns opposite to first-set of luminous parameters. For example, the object moving along the optical-axis towards the focal-plane may transgress the focal-point and accordingly arrive at a designated-location within the optical axis that corresponds to a distance less than the focal-length of the optical-system. Accordingly, the designated location in the present scenario corresponds to a position on the other side of focal plane, when compared with the initial-most position of the object prior to the movement.

In such a scenario, the focusing of the illumination beam is ceased (step108) based on current or a second set of luminous parameters exhibiting a numerical value like the first-set of luminous parameters but a numerical-representation (i.e. sign) ‘different’ than the first set of luminous parameters. More specifically, the numerical value of the second set of parameters is represented with the sign ‘opposite’ to the first set of parameters. Accordingly, the cessation of the focusing in the present scenario coincides with the arrival of the moving object at another designated-location closer to the focal-plane, as compared to aforesaid NULL position.

Overall, the arrival of the moving object at the focal-plane or beyond the focal-plane is electronically registered or detected either due to currently determined set of luminous parameters exhibiting a ‘NULL’ value or exhibiting a change in ‘sign’.

Thereafter, upon the cessation of focusing, the illumination of the object is caused by using a diffused beam to thereby cause generation of a subsequent-scattered beam. Projection of such subsequent-scattered beam causes formation of another luminous-representation at the array-detector, wherein such another luminous-representation may correspond to an image. An intensity-difference between the adjacent pixels of such another luminous-representation formed at the array-detector is monitored. Based thereupon, a focal-length of the optical imaging apparatus is adjusted until such monitored intensity-difference increases by a pre-determined threshold, to thereby cause a fine-focusing of the optical imaging apparatus.

Now referring toFIG. 1(b), the same also illustrates a method of focusing of an optical imaging apparatus, wherein the initial steps102,104and106astand equivalent to steps102,104and106ofFIG. 1a, respectively.

FIG. 1(b)depicts a scenario, wherein movement imparted at the step106aleads to arrival of the object at such a position in which it is examined whether the current set of luminous parameters as determined exhibit a same ‘sign’ as otherwise associated with the first-set of parameters determined in step104. Such type of examination has been depicted inFIG. 106(b).

In case the examination in step106aresults in ‘yes’, then the control flow gets transferred to step106a, wherein the object is further moved along the optical-axis towards the focal-plane. Accordingly, in such a scenario, the motion is again imparted along the optical-axis in the same direction as before, i.e. the step106arepeats itself and resultantly obtained current-set of parameters are checked for ‘numerical-value’ and numerical representation (i.e. ‘sign’) through the step106b.

The repetition of the steps106aand106btakes place until there is observed a change in sign associated with the currently-determined set of parameters, said sign change occurring due to either the numerical-value turning NULL or numerical-representation acquiring an opposite sign as compared to the first set of parameters. Accordingly, upon having obtained the examination-result in step106bas being “NO”, the control-flow progresses to step108. The step108ofFIG. 1astands equivalent to the step108ofFIG. 1b.

Modifications, additions, or omissions may be made toFIGS. 1aand 1bwithout departing from the scope of the present disclosure. For example, the operations may be implemented in differing order. Additionally or alternatively, two or more operations may be performed at the same time. Furthermore, the outlined operations and actions are only provided as examples, and some of the operations and actions may be optional, combined into fewer operations and actions, or expanded into additional operations and actions without detracting from the essence of the disclosed embodiments.

FIG. 2illustrates an example sequence of method steps, wherein the sequence is based on the method steps as depicted inFIGS. 1aand 1b. Accordingly, the method steps in the sequence as illustrated inFIG. 2may correspond to a particular step ofFIGS. 1aand1b.

At step202, the rotatable frame, hereinafter referred to as filter, is placed in a first position so as to cause production of an off-axis beam from the light-source. The off-axis beam denotes a beam offset from the optical-axis, but parallel to the optical-axis. As a result, the off-axis beam is transmitted through a beam-splitter and directed towards an object as intended for illuminating or irradiating the object. The present step202may correspond to the step102ofFIG. 1a.

At step204, owing to scattering of the off-axis beam from an object, a light-spot representation “Ii,j” may be formed. Such light-spot formation takes place based on capturing of the scattered beam from the object by the array-detector. Moreover, the light-spot as formed corresponds to a first detected position. The present step204may correspond to the step104ofFIG. 1a.

At step206, a ratio in the form of first set of parameters is calculated as F1=(A−B)/(A+B) in respect of the representation as rendered by the array-detector. As mentioned before, ‘A’ represents an instantaneous-power of the scattered-beam detected by one-half of the array detector. On the other hand, ‘B’ represents an instantaneous power of the scattered beam detected by the other half of the array detector. The array-detector renders the light-spot at either of the halves as a result of capturing of the scattered-beam as explained now.

A working-distance ‘W’ may represent a distance between the object and an objective lens of the corresponding optical device. When the working distance ‘W’ is smaller than a focal-length of the objective lens, the light-spot impinging the array-detector is detected in the lower-portion of the array detector. Accordingly, in such a scenario, ‘A’ (assumed to be power detected in upper-half) may be null, while ‘B’ (assumed to be power detected in lower-half) may have a considerable value.

In other scenario, when the working-distance is larger than the focal-length of the objective lens, then the light spot impinging the array-detector is detected in the upper portion of the array detector. Accordingly, ‘A’ may have a substantial-numeric value while ‘B’ is null. Accordingly, merely by observing or detecting the position of the light-spot on the array detector, it may be determined if the working-distance is larger or smaller than the focal-length of the microscope objective lens. The present step206may correspond to the step104ofFIG. 1a.

At step208, the numerical representation of the ratio is observed to determine a sign (mathematics) associated with the calculated ratio In an example, in case A>B, i.e. power detected in a particularly designated half (say right half) is greater than the other half (say left), then the mathematical sign as associated with a finally-obtained value as associated with F1 is ‘positive’. In the alternative, the mathematical sign is obtained as ‘negative’.

In other embodiments, F1 may instead be calculated as the center of mass of the light spot detected by the array detector along y axis of the detector. Accordingly, depending upon a current ‘y’ coordinate of the center of mass and the particular half of the array detector confining said coordinate, a sign of the y coordinate may be determined.

Based on the ‘sign’ information obtained in the step208, the direction of change in the working-distance is ascertained and recorded as an “old-direction” or “initial-direction”. As a part of pre-configured settings, outcome of a ‘positive’ or “+” sign in step208may denote a current-position of object as being away from the focus of the objective-lens. In such a scenario, the direction of change in the working distance is defined as a direction in which the movement of the object along the optical-axis leads to ‘reduction’ in the distance between the object and an objective lens. On the other hand, ‘negative’ or sign may indicate a current position of the object as being between the objective-lens and the focus of the objective lens, thereby indicating the existence of the object on the other side of the focus as compared to the position corresponding to the “positive” or “+” sign. In such a scenario of “negative sign”, the direction of change in the working distance also defined as a direction in which the movement of the object along the optical-axis leads to ‘reduction’ in the distance between the object and an objective lens. However, such direction of change in the working distance corresponding to “negative sign” is exactly opposite to the direction linked with the “positive” sign.

The present step208may correspond to the step106ofFIG. 1aor step106aofFIG. 1bto the extent of determination of numerical representation or sign.

At step210, based on the determined direction of motion in step210, the working-distance i.e. (the distance between the objective lens and object) is changed. The working-distance may be changed by an amount comparable with the ‘depth-of-focus’ as associated with the objective-lens. The present step210may also correspond to the steps106/106aofFIG. 1.

At step212, the instantaneous light-spot representation Ii,j of the object undergoing motion (as a result of the step210) as captured by the array-detector are recorded. The present step212corresponds to the step104ofFIG. 1.

At step214, the ratio F1 as otherwise calculated in step206is also consistently updated in accordance with the object undergoing motion as a result of the step210. The present step214may also correspond to the step104ofFIG. 1.

At step216, an instantaneous-sign of the numerical-representation of the ratio is observed and based thereupon, an instantaneous direction of motion required for change in the working-distance is ascertained. For example, if case there is a change in sign from positive to negative or vice-versa, then the instantaneously determined new sign is instead used as an indicator to change the existing direction. As may be understood, the motion-imposed upon object along the optical-axis continuously updates values of F1 and causes movement of the light-spot from the lower to upper half (or vice-versa), thereby leading to a possibility of change in mathematical sign of F1 during with the exhibited-motion. The present step216corresponds to the step106/106aofFIG. 1.

At step218, the instantaneous-direction as determined is compared with the old-direction as had been earlier determined in the step208. In case both are equivalent to each other, then the steps212till216repeat.

However, if the new direction is found different than the older one, then the control is transferred to the step220. In such a scenario, the instantaneous detected position of the object is considered as the second-detected position. Accordingly, the ratio as determined in step214and examined in step216with respect to the current or second set of luminous parameters is found either as NULL or as having a considerable numerical value and opposite sign than the first set of luminous parameters. The present step218specifically corresponds to the step106bofFIG. 1.

At step220, the rotatable filter is placed in a second position to enable production of a diffused beam from the light-source. Thereafter, the object may be focused through the automatic fine-focusing techniques (e.g. contrast-based sharpness method) as known in the art. Accordingly, the step220corresponds to step108.

Modifications, additions, or omissions may be made toFIG. 2without departing from the scope of the present disclosure. For example, the operations may be implemented in differing order. Additionally or alternatively, two or more operations may be performed at the same time. Furthermore, the outlined operations and actions are only provided as examples, and some of the operations and actions may be optional, combined into fewer operations and actions, or expanded into additional operations and actions without detracting from the essence of the disclosed embodiments.

FIG. 3illustrates an optical-system, interchangeably referred as an optical-imaging apparatus300, in accordance with an embodiment of the present subject matter. An objective-lens302is configured to project an illuminating-beam upon an object304to thereby cause generation of a scattered beam. Such illuminating beam may be an off-axis beam or a diffused-beam. For such purposes, an off-axis aperture306-1may be disposed against a source308of the optical-beam to generate an off-axis beam as the illuminating beam. A diffuser306-2may also be alternately disposed against the source308of optical-beam and configured to generate a diffused beam. The diffuser306-2may be adapted to substitute the off-axis aperture306-1during cessation of the focusing of the illuminating beam to thereby cause the illumination of the object by the diffused-beam and generation of another scattered beam.

For facilitating the interchangeability, a rotary frame (shown inFIG. 4toFIG. 6) supports the off-axis aperture306-1and the diffuser306-2and is rotatable by an actuator for interchangeably placing the off-axis aperture306-1and the diffuser306-2against the optical-beam to generate the illuminating beam and the diffused beam. The source of light may be a collimated light beam.

Further, a beam-splitter310is configured to transmit the illuminating-beam (whether diffused or off-axis) from the source308to the objective-lens302. An array detector312is configured to form a light-spot or image of the object based on the scattered beam from the object. A camera-objective lens314is configured to focus the scattered beam upon the array detector312. The array-detector312may be a charge coupled device (CCD) and configured to receive the scattered beam focused from the camera-objective lens314and render a light or image there-from.

A processing system (not shown in figure) constitutes the electronics of the optical-system300and is enabled by a computing-system. The processing system is connected to the array detector312for ceasing the performance of operations corresponding to the method steps104and106and accordingly continuously calculates the instantaneous position of the object undergoing motion as a part of focusing. Based on such calculations, the arrival of the moving object about the focal-plane is indicated by virtue of a numerical representation as exhibited by the second set of parameters (i.e. mathematical sign as associated with the value of F1). A computer system1400ofFIG. 14below is an example of the processing system.

An actuator (shown later inFIG. 6) may be triggered by the processing system upon derivation of the first set of luminous parameters and prior to derivation of the second set of luminous parameters. Such actuator is configured to execute a linear-movement of the object along an optical-axis in the first direction defined by the numerical-representation of the first set of luminous parameters to thereby enable focusing of the illumination-beam upon the object. More specifically, the processing system evaluates the function F1 with respect to an instantaneous position of the object, determines the direction in which the working-distance has to be changed and accordingly commands the actuator. The actuator linearly moves the object in a given direction towards the focal-plane of the optical-imaging apparatus300along the optical-axis, until the sign associated with the ratio F1 (as gathered by the corresponding numerical-representation) changes to ‘null’ or an opposite sign. If each step of motion imparted to the object by the linear-actuator is comparable in length to depth of focus of the objective-lens302, then at the moment of sign-change, the object resides at the distance smaller than a depth of focus. This may be an effective distance as attained for ceasing the currently pursued focusing (i.e. coarse focusing) and trigger a fine-focusing operation upon the object.

Further, the actuator may be further triggered to render an additional-type of motion as a rotary motion. The actuator is triggered by the processing system upon derivation of “NULL” or the second set of parameters to rotate and thereby align the diffuser with the illumination source to produce a diffused-beam. Accordingly, the actuator may cease the focusing of the off-axis illumination beam upon the object through the off-axis aperture and instead may trigger the focusing through the diffused-beam.

Further, a monitoring-module constituting the electronics of the optical system is configured to ascertain an intensity-difference between the adjacent pixels of the subsequent luminous-representation, i.e. the image formed at the array-detector, based on the projection of the scattered-beam from the object upon having been illuminated by the diffused-beam. Based upon the intensity difference as ascertained by the monitoring-module, a focal-length adjuster is configured to cause a fine-focusing of the optical imaging apparatus300by adjusting a focal-length of the optical imaging apparatus till the ascertained intensity difference increases by a pre-determined threshold.

FIGS. 5aand 5billustrate the rotatable-frame400pivoted over a block502and exhibiting two-different positions/states upon its rotation. The rotatable-frame400by virtue of its rotation places the off-axis aperture306-1and diffuser306-2in alignment with a passage within the block502at different instants of time, thereby leading to exhibition of two different positions: a first position and a second position.

In the first-position as depicted inFIG. 5a, the rotatable-frame400aligns the off-axis aperture306-1with the collimated-beam of light, thereby forming an off-axis collimated beam having a smaller-diameter. Such off-axis beam, after having been transmitted through the beam-splitter310and directed by the objective302lens upon the surface of the object304, impinges the object304in an off-axis spot. The position of such spot is later detected by the array-detector312, for example, as represented inFIG. 7, andFIG. 8. In the second position as depicted inFIG. 5b, the frame400places the diffuser306-2in the path of the collimated beam, and transforms the optical system300into a common reflective microscope.

FIG. 6illustrates a bottom-view of the assembly of the rotatable frame400with the block502as shown inFIG. 5, thereby depicting an actuator602for rotating the rotatable-frame400with respect to the block502. The actuator602upon rotation substitutes the off-axis aperture306-1with the diffuser306-2and vice versa also, thereby discretely aligning and de-aligning the off-axis aperture306-1and diffuser306-1with respect to the collimated light-beam. The actuator602as connected to the rotatable-frame400may be a rotary motion source. In addition, the actuator602may also configured to exhibit a translation-motion (e.g. through a lead-screw mechanism) to execute the motion of the object along the optical-axis in line with the steps106,106a, and210inFIG. 1a,FIG. 1bandFIG. 2.

As can be observed fromFIG. 7, when the working distance (W) is smaller than focal length of the objective lens, the light spot impinging the array detector is located in the lower portion of the array detector (as exemplarily depicted inFIG. 7aandFIG. 7b). When the working-distance is larger than the focal-length of the microscope objective the light spot impinging the array detector is located in the upper portion of the array detector (as exemplarily depicted inFIG. 7dandFIG. 7e). By observing the position of the light spot upon the array detector, it may be determined if the working distance is larger or smaller than the focal-length of the objective-lens.

As a matter of quantifying position of the light-spot impinging array-detector by the processing system, an example implementation has been provided. As per the factory settings, the centre of the off-axis aperture within the rotatable-frame is placed along y axis of the array detector in accordance with the plane of the figure as shown inFIG. 3. Upon defining a coordinate of the array detector along the horizontal axis ofFIG. 3, a function may be defined that characterizes position of the light spot as the first/second set of luminous parameters as would be seen by a two-segment position sensing detector.
F1=(A−B)/(A+B)

wherein

wherein

the i index extends along y-axis,

and j-index extends along x axis,

N, M are number of pixels of array detector in y and x direction respectively, and

Ii,jis the power of light impinging pixel having indexes i,j.

In another implementation, the first/second set of luminous parameters as designated by F1 may be derived as a ‘y’ coordinate of center of mass (Cmy) of the observed light spot in respect of the center of the detector N/2 and M/2:

wherein

the i index extends along y-axis,

and j-index extends along x axis,

N, M are number of pixels of array detector in y and x direction respectively, and

I i,j is the power of light impinging pixel having indexes i,j.

FIG. 8illustrates a graphical-representation illustrating a plot of F1 as a function of the distance between sample and focal plane. While the presentFIG. 8has considered the ratio F1 as

(A-B)(A+B),
in another example F1 may also correspond to a centre of mass (Cmy) as earlier discussed inFIG. 7

In the present graphical representation, while the y-axis represents F1, x-axis represents an identifier corresponding to the working-distance and focal-length. Such identifier may be in turn a ratio denoted by (WD−F)/F, wherein WD is the working-distance and F is the focal length of the microscope objective-lens. Accordingly, the graphical-representation ofFIG. 8may be appropriated to determine as to whether the object is too close or far from the focal plane of objective-lens.

As may be inferred from the representations in theFIGS. 7 and 8, the optical system300when operating in the first position (i.e. off-axis aperture in alignment with the collimated-beam) may detect using a single measurement, as to whether the distance between the sample and the objective lens objective lens is too small or too large.

FIG. 9illustrates a method of auto-focusing of an optical imaging apparatus in accordance with another embodiment of the present subject matter.

The method comprises causing (step902) illumination of an object using an illuminating beam to thereby cause generation of a scattered-beam and corresponds to the step102ofFIG. 1.

Further, a set of luminous parameters are derived (step904) from a currently detected position of a luminous-representation of the object, wherein the luminous-representation is based on projection of the scattered beam and corresponds to a light-spot. The position-attribute within the set of parameters corresponds to a current-position of a centre of mass of the light-spot with respect to a focal plane of the optical imaging apparatus, the centre of mass being detected through the array-detector. Such position-attribute associated to the set of luminous parameters is analysed to enable calculation of a distance required to be traversed as a part of movement along the optical-axis to attain the auto-focusing.

The direction and distance as calculated from the set of luminous parameters is based on a pre-determined criteria established during historical-autofocusing exhibited by the optical-imaging apparatus. The criteria may be a pre-derived relation between:

(a) a distance traversed by the object along the optical-axis during the historically conducted autofocusing; and

(b) a horizontal/vertical shift exhibited by the center-of-mass of the light-spot in an array-detector during such autofocusing.

Further, the method comprises performing (step906) an auto-focusing operation by triggering movement of the object along an optical-axis in a designated direction. Such direction of movement is dependent at-least upon the position-attribute within the set of parameters. Further, as a part of autofocusing, the distance covered by the object during the movement is also determined from the position-attribute.

FIG. 10illustrates an example implementation of the method steps as depicted inFIG. 9. More specifically,FIG. 10illustrates process as needed for defining the criteria as otherwise needed execution of the method step906, i.e. derivation of the direction and distance as required for defining a movement of the object along the optical-axis during the autofocusing. Such process may be executed during a normally executed auto-focussing operation of the object to set the aforesaid-criteria that may be later applied during the performance of method steps ofFIG. 9.

At step1002, during the autofocusing, a position corresponding to a ‘best-focus’ position upon the optical-axis may be noted or logged. In an example, such ‘best-focused’ image is determined through any of known autofocusing (e.g. contrast-detection based, phase-detection based) or fine-focusing techniques as associated with the optical-imaging devices. In other example, the best-focus image may also be determined through manually performed fine-focusing techniques. Once determined, the position corresponding to the ‘best-focus’ image may be logged either manually or electronically using the existing (slow) autofocusing routine.

At step1004, various images may be captured through the array-detector with respect to equally spaced z-axis positions above and below ‘best focus’ position found in step1002. More specifically, the object as focused upon in step1002may be displaced along the optical-axis (i.e. z-axis) by equal amounts (i.e. steps) at either side of the ‘best-focus’ position and resultant luminous-representation at such lesser-focus' positions may be captured through the array-detector.

At step1006, a background-luminosity with respect to captured images in step1004may be determined by finding a median over all pixels for each image, separately. Thereafter, x and y components of the ‘centre of mass of light-spot’ i.e. may also be captured with respect to each image separately.

More specifically, Cmxmay be calculated as the ‘x’ coordinate of center of mass of observed light spot in respect of the center of the detector N/2 and M/2:

Likewise, Cmymay be calculated as the ‘y’ coordinate of center of mass of observed light spot in respect of the center of the detector N/2 and M/2:

wherein

the i index extends along y-axis,

and j-index extends along x axis,

N, M are number of pixels of array detector in y and x direction respectively, and

I i,j is the power of light impinging pixel having indexes i,j.

At step1008, a relationship is obtained that depicts variation between a) the Cmxand Cmycomponents as determined in step1006and b) z coordinate correspond to various z-axis positions as determined in step1004. In an example, such relationship may be linear or approximately linear.

The aforesaid steps from1004till1008may be executed (as a part of defining the aforesaid criteria) once or twice in a day during the autofocusing and may be termed as a calibration exercise with respect to the optical-system300.

FIG. 11illustrates an actual-photographical representation of the shift of the centre of mass of light spot during an autofocus mode in accordance with an implementation of the method steps ofFIG. 10. More specifically, the different images as depicted correspond to the step1004. As depicted in the present figure, various images or light-spots as captured correspond to equally-spaced different positions of the object along the z-axis (i.e the optical axis). Such positions along the z-axis have been depicted in terms of ‘number’ of steps as well as in millimeters.

FIG. 12illustrates a graphical representation in respect of shift of the center of mass of light spot during an autofocus mode, in accordance with an implementation of the method steps ofFIG. 10. More specifically, the graphical-representation in presentFIG. 12corresponds to the relation as calculated during the method step1008and depicts the variation of each of the x and y components of the centre of mass of the light-spot against a variation in position of object along the z-axis (i.e. the optical-axis). More essentially,FIG. 12depicts two kinds of relationship as follows:

a) variation in Cmxversus variation in position along z-axis.

b) variation in Cmyversus variation in position along z-axis.

FIG. 13illustrates another example-implementation of the method steps as depicted inFIG. 9.

At step1302, a light-spot is formed at the array-detector through aligning an off-axis aperture with the collimated beam and obtaining a scattered beam from the object illuminated by the off-axis beam. The present step1302corresponds to the step902.

At step1304, a background-luminosity is subtracted with respect to the current image at the array-detector. A centre of mass of the current light-spot, as detected by the array detector along x and y axis of the detector, is calculated as Cmxand Cmy. The present step1304corresponds to the step904.

At step1306, the currently obtained Cmxand Cmyin step1304are compared with the pre-determined criteria (i.e. relationship) as illustrated inFIG. 12. Using such data and criteria established earlier during calibration, it is determined as to how much and in what direction the position of the object along the z-axis needs to be changed as a part of autofocusing. The present step1306corresponds to the step906.

At step1308, based on direction and distance as determined in step1306, the object is moved along the optical-axis towards the focal plane of the objective lens to attain auto-focusing. The present step1308corresponds to the step906.

FIG. 14shows yet another example implementation in accordance with the embodiment of the present disclosure. More specifically, the present figure illustrates a typical hardware configuration of the processing system and monitoring module (as linked with linked optical-system300ofFIG. 3) in the form of a computer system1400is shown. The computer system1400can include a set of instructions that can be executed to cause the computer system1400to perform any one or more of the methods disclosed. The computer system1400may operate as a standalone device or may be connected, e.g., using a network, to other computer systems or peripheral devices.

In a networked deployment, the computer system1400may operate in the capacity of a server or as a client user computer in a server-client user network environment, or as a peer computer system in a peer-to-peer (or distributed) network environment. The computer system1400can also be implemented as or incorporated across various devices, such as a personal computer (PC), a tablet PC, a personal digital assistant (PDA), a mobile device, a palmtop computer, a laptop computer, a desktop computer, or any other machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. In an example implementation, the computer system1400may be a mobile computing cum display device capable of being used by a user. Further, while a single computer system1400is illustrated, the term “system” shall also be taken to include any collection of systems or sub-systems that individually or jointly execute a set, or multiple-sets, of instructions to perform one or more computer functions.

The computer system1400may include a processor1402e.g., a central processing unit (CPU), a graphics processing unit (GPU), or both. The processor1402may be a component in a variety of systems. For example, the processor1402may be part of a standard personal computer or a workstation. The processor1402may be one or more general processors, digital signal processors, application specific integrated circuits, field programmable gate arrays, servers, networks, digital circuits, analog circuits, combinations thereof, or other now known or later developed devices for analysing and processing data The processor1402may implement a software program, such as code generated manually (i.e., programmed).

The computer system1400may include a memory1404, such as a memory1404that can communicate via a bus1408. The memory1404may include, but is not limited to computer readable storage media such as various types of volatile and non-volatile storage media, including but not limited to random access memory, read-only memory, programmable read-only memory, electrically programmable read-only memory, electrically erasable read-only memory, flash memory, magnetic tape or disk, optical media and the like. In one example, the memory1404includes a cache or random access memory for the processor1402. In alternative examples, the memory1404is separate from the processor1402, such as a cache memory of a processor, the system memory, or other memory. The memory1404may be an external storage device or database for storing data. The memory1404is operable to store instructions executable by the processor1402. The functions, acts or tasks illustrated in the figures or described may be performed by the programmed processor1402executing the instructions stored in the memory1404. The functions, acts or tasks are independent of the particular type of instructions set, storage media, processor or processing strategy and may be performed by software, hardware, integrated circuits, firm-ware, micro-code and the like, operating alone or in combination. Likewise, processing strategies may include multiprocessing, multitasking, parallel processing and the like.

As illustrated, the computer system1400may or may not further include a touch-sensitive display unit1410, for outputting determined information as well as receiving a user's touch-gesture based inputs, such as drag and drop, single tap, multiple-taps, etc. The display1410may act as an interface for the user to see the functioning of the processor1402, or specifically as an interface with the software stored in the memory1404or in the drive unit1406.

Additionally, the computer system1400may include an input device1412configured to allow a user to interact with any of the components of system1400. The computer system1400may also include a disk or optical drive unit1406. The disk drive unit1406may include a computer-readable medium1418in which one or more sets of instructions1414, e.g. software, can be embedded. Further, the instructions1414may embody one or more of the methods or logic as described. In a particular example, the instructions1414may reside completely, or at least partially, within the memory1404or within the processor1402during execution by the computer system1400.

The present disclosure contemplates a computer-readable medium that includes instructions1414or receives and executes instructions1414responsive to a propagated signal so that a device connected to a network1426can communicate voice, video, audio, images or any other data over the network1426. Further, the instructions1414may be transmitted or received over the network1416via a communication port or interface1420or using a bus1408. The communication port or interface1420may be a part of the processor1402or may be a separate component. The communication port1420may be created in software or may be a physical connection in hardware. The communication port1420may be configured to connect with a network1416, external media, the display1410, or any other components in computing system1400, or combinations thereof. The connection with the network1416may be established wirelessly as discussed later. Likewise, the additional connections with other components of the system1400may be established wirelessly. The network1416may alternatively be directly connected to the bus1408.

The present subject matter enables optical-systems, such as microscope, to enable an automatic focusing upon the objects lying away from the focal plane with and ease of operation. More specifically, the present subject matter facilitates the optical systems to enable detection of a type of distance-variation required in terms of the object for focusing, irrespective of the quality of object-image as formed. Moreover, a range of the working distance over which the optical-apparatus may be used for autofocusing of the image is large.

The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein.

Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.