Automated apparatus to obtain images in incremental focal-distance steps using either focus ring rotation or linear translation methods

Abstract

Because of modern computers and digital cameras, it is now possible to take a series of photographs at incremental focus distances and then combine all of these into a single composite photograph. There are three ways to acquire the stepwise images, either manually or automatically. This invention allows all three methods to be executed using a single automated apparatus by using different means of positioning/moving the camera or lens. This includes external rotation of the focus ring (1), or linearly moving the camera and lens together (2), or moving just the camera (3a), or moving just the lens (3b) in highly controlled steps, thus allowing rapid collection of many images, each at incremental focus depths into the subject. These stacks can then be processed using any of several commercial software packages to combine all the images into a single high-resolution composite image.

Claims

1) An apparatus and method to automatically obtain images in incremental focal-distance steps using any of three possible methods, all involving use of a stepper motor to drive a lead screw and platform in controlled steps while taking a photograph at each step, or while continuously recording a video.

2) method of claim 1 wherever a controller provides the means to energize the stepper motor manually, or is able to program the motor functions and trigger the camera sequentially, and which allows setting the following parameters; motor speed, number of steps, angular change per step, and delay time between steps,or instead allows continuous video filming during the sequential focus changes.

3) The method of claim 1 in which the focus change is achieved by controlled rotation of the focus ring using a lead screw rotated by the stepper motor.

4) The method of claim 3 using a Z-shaped support structure wherein the camera/lens are mounted on the top of platform and the motor/leadscrew/rail mechanism on its base, by which the motor driven screw causes horizontal movement of a plate mounted on a moving platform confined to a rail which in turn, through magnetic coupling, moves a rigid tab extending down from the focus ring, thereby rotating the ring.

5) The method of claim 3 in which the camera/lens is mounted above and on the end of a commercial stepper motor/linear rail/lead-screw device in such a way that by extending the lead screw out beyond the end, a pulley gear can be attached to it and by then adding a gear band to the focus ring, a pulley-gear-band can couple the drive gear below to the focus ring above, allowing the stepper motor to control rotation of the focus ring.

6) method of claim 1 whereby the focal distance is changed simply by moving the camera/lens together, such that the images are sequentially taken in focal steps from the very front to the very back of the subject.

7) method of claim 6 whereby the camera/lens is mounted on a moving platform, being caused to move horizontally on a linear rail by means of a stepper motor/lead screw coupled directly to the platform by means of a nut threaded onto the screw but restricted from rotation by being attached to the moving platform, which is itself confined to a rail.

8) The method of claim 1 in which the camera and the lens are connected via a bellows and the two elements are connected independently to the apparatus structure.

9) The method of claim 8 whereby the lens is attached to the rigid support structure and the camera is mounted on a platform which in turn, is mounted on a linear rail and caused to move horizontally by means of the stepper motor/lead screw through a threaded nut on the lead screw but which is restrained from rotation by being attached to the platform thereby allowing images to be sequentially taken in focal steps from the very front to the very back of the subject.

10) method of claim 8, whereby the camera is attached to the rigid support structure and the lens is mounted on a platform which in turn, is mounted on a linear rail and caused to move horizontally by means of the stepper motor/lead screw through a threaded nut on the lead screw but which is restrained from rotation by being attached to the platform thereby allowing images to be sequentially taken in focal steps from the very front to the very back of the subject.

11) method in claim 1 whereby the images are obtained by video recording while the focal distance is simultaneously changed stepwise, using controller settings in terms of speed and step size optimized to match the video frame rate of capture, such as for claim 3, Method 1covering 20 degree rotation in 20 seconds, thereby capturing 140 frames with a 7 frame per second video camera speed and adjusting the delay time between steps to deliver optimum clarity in individual frames.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0042] The drawings describing the invention in its's various forms and related information are as follows:

[0043] 1. The Magnification factor (1:x) is plotted for various focal length lenses and manufacturers as a function of distance to the subject showing larger changes the smaller the focal distance of the lens

[0044] 2. The focus ring angle for 60 mm, 105 mm and 200 mm lens is plotted as a function of distance to the subject, showing strong non-linearity for all lenses, with the highest distance/angle ratio being at short distances, <1 m.

[0045] 3. This figure shows how a commercial motor-driven, linear rail can be adapted to execute focus ring rotation (Method 1) by extending the leadscrew and using a pulley gear-band to connect the pulley gear at the end of the leadscrew to the focus ring barrel above.

[0046] 4. This figure shows a Z-channel mounted motor/lead screw/moving plate (magnet) method to rotate the focus ring (Method 1) by means of a rigid arm extending down from the focus ring.

[0047] 5. This figure shows a block diagram for creating linear translation of the camera and lens together (Method 2)

[0048] 6. This figure shows a Z-channel mounted motor/lead screw/moving platform/magnet confined to a rail in order to move just the camera, with the lens fixed in place (Method 3)

[0049] 7. This figure shows a Z-channel mounted motor/lead screw/moving platform/magnet confined to a rail in order to move just the lens, with the camera fixed in place (Method 3)

[0050] 8. This figure shows a Block Diagram for the electronic system.

DETAILED DESCRIPTION OF THE INVENTION

[0051] Before discussing the figures in detail, the three methods are first described in general, especially to explain resolution characteristics which vary by a factor of 3 or more, but which are all better than required for most applications.

[0052] Method 1 Focus Ring Rotation

[0053] In one configuration (A), a commercial motor/lead screw/linear rail system is adapted by extending the lead screw out from the system end plate, adding a drive gear to the end of the screw and also mounting the camera/lens on top of the end plate in such a way that a gear band on the focus ring aligns with the drive gear below and thereby, through use of a pulley gear band allows motor axle rotation to rotate the focus ring. Note in this use, that the lead screw pitch as no role in performance but is just an extension of the motor axle. (See FIG. 3). Using a second configuration (B), the camera and lens are placed at 90 degrees to the direction of the motorized lead screw. The camera is paced on top of a Z channel support structure while the motor and lead screw are mounted below, such that a moving nut/vertical plate passes below.

[0054] Using magnetic coupling to a rigid arm extending down from the focus ring, it can be caused to rotate. The advantage of this method over configuration (A) is that the sensitivity/resolution in terms of angular rotation is about three time better for (B) because of the different geometry involved and because the pitch of the lead screw is now an important factor. (See FIG. 4).

[0055] The means of attachment of the camera and lens to execute Method 2 or Method 3 is the same whether using configuration (A) or (B), hence the step size resolution is the same.

[0056] Method 2Linear Translation of the Camera and Lens

[0057] In this method, the camera and lens are mounted directly on the moving platform driven by the stepper motor/leadscrew/rail mechanism as already provided by commercial systems (Cognisys, Wemacro).

[0058] Method 3Linear Translation of Just the Lens, or Just the Camera.

[0059] In this method, instead of attaching the camera and lens together to the moving platform, the lens and camera are instead separated by a bellows which allows the two components to move independently. Either the camera or the lens can be mounted on the moving platform, the other being held fixed by the structure/base.

[0060] Regarding sensitivity, of the three methods, barrel rotation (Method 1) provides smaller step size capability and reduced magnification effects compared to both Method 2 and Method 3, but all methods provide more than adequate performance. Using Helicon software for the image stacking process, we do observe improved clarity/resolution in final images using Method 1, compared to Method 2 and we also expect Method 3 to be better than Method 2 when the lens is held fixed and the camera is moved to change the focal distance. Which of the methods is best may ultimately be determined by changes in the focus stacking software to accommodate one image collection method better than the others. Note that the appropriate step size in terms of focal distance change is mainly determined by the depth of field (DOF) at the desired working distance. If imaging through microscopic lens, the DOF is often well less than 0.1 mm. For other lens with large apertures used to obtain the sharpest focus, the DOF can be 1 mm or so. Since it is desirable to overlap in-focus regions in the stack, it is common practice to use DOF as a criteria for selecting step size. Having said that, and disregarding the special situation of microscope lens, it is clear the depth resolution of 0.01 mm will be adequate for most work and in our experience, 0.1 mm step size is often enough. All three methods and the various embodiments of this invention achieve smaller step sizes than needed. The minimum for Methods 2 and 3 is 0.01 mm. Method 1, using configuration (B) offers the smallest step size by virtue of the leadscrew mechanical advantage, coupled to the 3 effect of using a rigid arm extension from the focus ring to affect its rotation, being about 0.003 mm in terms of focal distance change. If needed, smaller step sizes can be obtained by using a finer leadscrew pitch. The sizes given here refer to a screw with 1 mm pitch.

[0061] The relevant figures for each method are now described as follows. Each figure has details labeled by text labels or numerically and will be referred to as 1.1, 1.2, . . . 2.1, 2.2 . . . Etc.

[0062] FIG. 1 shows the magnification changes as a function of distance for several lens demonstrating the strong dependence for short focal distance lens, being a factor of 10 for the 40 mm lens from 0.2 m (shortest distance possible) to just 0.4 m (0.2 m total). The progression is very regular going from 40 mm to 200 mm. At 200 mm the magnification change is only about 3 while going from 1 m to 0.5 m (0.5 m total) The straight lines come from the simple expression derived through optical physics and shown earlier. Magnification is directly proportional to the lens focal length (f) and inversely proportional to the distance to the subject (p).

[0063] FIG. 2 shows the relation for Method 1 of the focal ring angle to distance from the subject for three examples; Sigma-105 mm, Nikon-200 mm and Canon-60 mm lens. We show these in part to demonstrate that different lens and manufacturers do have somewhat different characteristics, but have a common feature in having a much larger focus ring change at short distances (<1 m), a knee at around 1 m and have a relatively smaller angular change at distance >1 m. Both regions are thus covered by angular changes of about 100-150 degrees each. In our experience, at short distance to the subject we often need 10 to 50-degree rotation for macro photography but smaller changes are needed at longer distances used for example in product imaging and smaller yet for landscape photography.

[0064] FIG. 3 Commercial motor-driven, linear rail adapted to execute focus ring rotation This figure provides a block diagram showing how a commercial motor driven linear rail can be adapted to execute Method 1 (Structure A) by positioning the camera/lens in such a way that an extension of the lead screw, through a pulley-gear is able to rotate the focus ring. In this figure, the commercial rail system is shown as a side view and is confined by a base and two end plates (3.1, 3.4). The moving platform (3.13) normally used to move mounted objects horizontally can be either ignored or removed as it is not used in this adaptation. Normally, the lead screw (3.3) does not extend beyond the end plate (3.4), but by using a longer lead screw, it can be modified such that the lead screw does extend out beyond the frame end. A small diameter pulley gear (3.5) can be attached directly to the lead screw end as shown. This drive gear (3.5) interfaces with a pulley gear band (3.8) which in turn interfaces to a gear band (3.10) that is attached to the focus ring (3.9). Though not shown here, a freewheeling pulley gear can also be added to the end plate (3.4) in such a way as to provide a tensioning mechanism to the pulley gear band (3.8). As shown, the camera (3.12) and lens (3.11) are mounted on a quick release plate (3.7). The plate is held by the clamp (3.6) which is attached directly to the end plate (3.4). The camera and lens can be easily moved to position the focus ring gear band (3.10) directly above the drive gear (4.5) below. Note that the pitch of the lead screw has no impact on the sensitivity as it is merely an extension of the motor drive axle in this use.

[0065] FIG. 4 is a drawing of the all-in-one apparatus capable of executing all three Methods (1,2,3) and in this embodiment configured to execute Method 1 in which the focus ring is rotated to vary the focal distance, while the camera and lens remain in place. In this case, the camera/lens (4.9) is mounted to the top surface via a quick connect clamp (4.8). A clamp on the focus ring (4.10) secures an L-shaped tab (4.11) extending down to near the lower horizonal surface (4.6). The stepper motor (4.1) and linear rail (4.7) are attached to the lower surface (4.6). A moving platform (4.3) rides on the rail, confined by ball bearings to grooves on each side of the rail (4.7). The stepper motor (4.1) turns a lead screw (4.2). A nut on the lead screw is attached to the moving platform via a U-shaped structure (4.12), thus restraining it from rotation and forcing horizontal movement of the platform and attached bar magnet (4.5). The bar magnet connects by magnetic force to the roller bearing (4.4) attached to the lower leg of the rigid arm (4.11). As the magnet moves horizontally, the focus ring rotates in either clockwise or counterclockwise direction depending on the direction of the moving platform.

[0066] Note that by removing the bar magnet and its backing plate required for Method 1, the top surface of the U-shaped structure (4.12) riding on the linear rail platform (4.3) becomes available to execute either Method 2 or Method 3.

[0067] FIG. 5 shows a block diagram for Method 2, where the camera and lens are moved together on a horizonal plate (5-10). In this case the camera (5.9) and lens (5.8) are connected to a plate (5.10), held by a quick-release clamp (5.11), which is itself connected to a rigid, inverted L-shaped arm/platform (5.7). In the previous FIG. 4), the U-shaped platform/arm (4.12) serves the identical function depicted here as element (5.7). This arm is mounted on a moving platform (5.4). The platform keeps the nut from rotating, thus forcing linear movement in the horizonal direction. The platform contains small bearings that are confined to grooves on either side of the steel rail (5.5). The nut (5.3) is moved by rotation of a 1 mm pitch lead screw (5.6), which is driven by a Nema 17, 2A stepper motor (5.1). The motor (5.1) and rail (5.5) are mounted to the bottom surface of the Z-shaped channel (5.2).

[0068] FIG. 6 is a detailed drawing for configuring Method 3, wherein the lens is fixed in place and the camera is attached to the moving platform. The lens (6.10 is attached to a quick release clamp (6.11) which in turn is connected to the top horizontal portion of the support structure (6.7). The support structure is mounted on a tripod (6.4) at the bottom horizontal portion of the structure (6.1). The lens (6.10) is attached to the camera (6.8) with a flexible bellows (6.9) such that the lens remains fixed, but the camera can move horizontally. To achieve this, the camera is mounted to a quick release clamp (6.5) which is itself attached to a moving platform (6.3). The platform is moved horizontally by means of a stepper motor (6.12) that turns a lead screw (6.6) and which in turn causes a nut to move horizontally because the nut is restrained from rotating by attachment to the moving platform (6.3). The moving platform is restrained to a rail (6.2) via ball-bearings attached to the platform and which are also confined to grooves on each side of the rail. The motor (6.12) and rail (6.2) are mounted to the lower portion of the support structure (6.1).

[0069] If instead of attaching the lens to the solid structure as shown here, the bellows (6.9) can be removed and the lens (6.10) can be attached directly to the camera. This then is the configuration needed to execute Method 2, where the camera and lens are moved together to change the focal distance.

[0070] FIG. 7 is a detailed drawing for Method 3 wherein the camera is fixed in place and the lens is attached to the moving platform. The camera (7.1) is attached to a quick release clamp (7.5) which in turn is connected to the top horizontal portion of the support structure (7.13). The support structure is mounted on a tripod at the bottom horizontal portion of the structure (7.11). The lens (7.2) is attached to the camera (7.1) with a flexible bellows (7.4) such that the camera remains fixed, but the lens can move horizontally. To achieve this, the lens is mounted to a quick release clamp (7.7) which is itself attached to a moving platform (7.8, 7.9). The platform is moved horizontally by means of a stepper motor (7.6) that turns a lead screw (7.14) and which in turn causes a nut to move horizontally because the nut is restrained from rotating by attachment to a U-shaped support (7.8) which in turn is connected to the moving platform (7.9). The moving platform is restrained to a rail (7.10) via ball-bearings attached to the platform and which are also confined to grooves on each side of the rail. The motor (7.6) and rail (7.10) are mounted to the lower portion of the support structure (7.11). Note the focus ring (7.3) is not rotated in this method but the focal distance is changed by moving the entire lens (7.2) relative to the camera (7.1).

[0071] FIG. 8. shows a block diagram for the electronic control system. More details concerning it are provided in another patent submission titled Method and hardware to automatically obtain images in incremental focal-distance steps using any camera/lens having a rotatable focus ring. The control system can manage all three methods of operation described in this invention and the block diagram provides key elements of its functions.

[0072] As shown in the labels in this figure, the controller includes an embedded microcontroller board and is connected to a stepper motor control integrated circuit (IC), a liquid crystal display (LCD) board with keypad switches, and relays for camera shutter activation. One of many possible microcontrollers that could be used is the Microchip Atmega328P with integrated RAM, Flash and EEPROM memories.

[0073] The motor control IC (Allegro A4988) accepts digital input signals (digital outputs from the microcontroller) for:

TABLE-US-00003 Enable (supply power to stepper motor coils) Step (move motor one increment) Motor Direction (forward or reverse) Step Resolution (amount of each motor movement increment, set using MS1, MS2, MS3 ([Micro Step] digital inputs)

[0074] The A4988 IC is designed to operate standard bipolar stepper motors in full, half, quarter, eighth, and sixteenth-step modes.

[0075] Two camera control relays connect two contacts to a common third contact to command a connected digital camera to take a photograph. The microcontroller activates each relay using digital output pins connected to the relay coils.

[0076] The display/keypad board is connected to one of the microcontroller's serial communication peripherals (inter-integrated circuit port). The microcontroller sends commands for display of characters on the LCD and to read the state of the keypad switches. The LCD provides two rows of 16 characters for displaying/modifying system settings, activating motor movements and camera control sequences, and displaying the progress of an active shooting sequence.