WO1997013180A1

WO1997013180A1 - Projector slit lens assembly adjustment device

Info

Publication number: WO1997013180A1
Application number: PCT/US1996/015768
Authority: WO
Inventors: Daniel Leimeter
Original assignee: The Todd-Ao Corporation
Priority date: 1995-10-04
Filing date: 1996-09-30
Publication date: 1997-04-10
Also published as: AU7384196A

Abstract

A device and method are described for use with a motion picture projector which has a slit lens assembly (14) that focuses a bright slit of light (60) onto the soundtrack of film, which enables precise positioning of the slit lens assembly while discouraging repositioning by projector operating personnel. The device includes a holder clamp (102) that is clamped onto a portion (24) of the projector frame, a slit lens assembly clamp (106) that is clamped onto the slit lens assembly, and a lead screw (110) that connects the clamps of the device. When a projector frame clamp arrangement (40) is loosened to allow movement of the slit lens assembly, the lead screw is turned to precisely advance the slit lens assembly toward or away from the film plane until a maximum high frequency test response is obtained. The slit lens assembly clamp includes an inner part threadably connected to a screw (114) that clamps to the slit lens assembly, and an outer part that supports the inner part in rotation about the slit lens assembly axis while itself being coupled to the lead screw.

Description

PROJECTOR SLIT LENS ASSEMBLY ADJUSTMENT DEVICE

BACKGROUND OF THE INVENTION

Motion picture projectors include a soundtrack region where a thin slit of light is focused onto the soundtrack, light passing through the soundtrack is detected by a photocell to generate an electrical signal, and the signal is amplified and used to drive a theater loudspeaker system.

In the past, film frames of a motion picture film were spaced by four perforations (0.748 inch, or 19mm), so with the frames being advanced at 24 frames per second, the film moved at about 18 inches (457mm) per second past the sound head region. It is generally accepted that sound up to about 12.5kHz or 13 kHz must be reproduced with a "flat" response in a commercial motion picture theater to obtain acceptable theater sound quality. With film moving at 18 ips (inches per second, or 457mm per second), current theater projectors have generally been able to produce such a flat response. The slit of light at the soundtrack is produced by directing light through a slit lens assembly that forms a thin slit image, with the slit image generally having a nominal height of 0.5 mil (1 mil equals one- thousandth inch, or 0.127mm). With film moving at 18 ips (457mm per second), a tone of 12.5 kHz has a wavelength of 1.4 mils (0.036mm), and a half wavelength of 0.72 mil (0.18mm). Thus, even if the slit was somewhat out of focus so its effective height was up to 150% of its nominal height (i.e. 0.75 mil instead of 0.5 mil, or 0.019mm instead of 0.0127mm), the height of the slit image was still substantially no more than one-half wavelength of the highest frequency sound of interest (12.5 kHz) Reproducibility of sound begins to decrease as the slit height increases above one-half wavelength of the highest frequency to be reproduced.

A new motion picture format, described in U S patent 5,534,954, spaces the film frames by 2.5 perforations or about 0.467 inch (1 1 ,9mm), which is 5/8ths of the previous frame spacing. With the film moved at 24 or 30 frames per second, the film speed is only 62.5% or 78% of current film speed. As a result, sound of 12.5 kHz has a half wavelength of 0.45 or 0.56 mil (0.0114mm or 0.0142mm). Accordingly, it is important that the slit of light be very sharply focused on the soundtrack for minimal nonflatness of the generated sound signal

Most current motion picture theater projectors include a slit lens assembly with a cylindrical tubular housing, which is held by the projector frame The projector frame has a portion with a substantially cylindrical passageway, and forms a frame clamp arrangement or clamper along the passageway that can be deflected sidewardly against the slit lens housing to clamp it in place To adjust the slit lens assembly the clamper is loosened, a technician monitors sound produced by a test film, and the technician grasps the slit lens housing with his hand and moves it slightly forward or rearward along its axis while turning it slightly When the test instrument indicates a maximum high frequency output, the technician turns the bolt to clamp the slit lens assembly in place.

In practice, a technician cannot hand position the slit lens assembly with sufficient accuracy to produce a sharp slit lens image on the soundtrack After shifting the slit lens assembly back and forth for 15 minutes, the technician may decide that the response is "good enough ' The slit image may be left somewhat out of focus, and turned by several degrees from its ideal horizontal orientation which also degrades the output. An apparatus and method for adjusting slit lens position along the axis and/or in rotational position about the axis, which enabled precise adjustment of the slit lens assemblies of currently-m-use projectors, and which discouraged readjustment by unqualified personnel, would be of value.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, an apparatus and method are provided for positioning slit lens assemblies that are located in the sound head regions of current motion picture theater projectors, which enables precision positioning of the assemblies by skilled technicians while discouraging adjustment attempts by less skilled theater operators The adjustment apparatus includes a holder clamp that clamps to the projector frame, a slit lens assembly clamp that clamps to the slit lens assembly, and a lead screw that is connected between the clamps and that can be turned to precisely adjust the position of the lens assembly along its axis Both clamps of the device are only temporarily attached, and are removed after precision positioning, to discourage attempts at adjustment by less skilled personnel The slit lens assembly clamp includes an inner part that is clamped to the slit lens assembly and that can rotate within an outer part that is coupled to the lead screw Accordingly, after the slit lens assembly is precisely positioned at its optimum axial position, the inner part can be turned to position the assembly at its optimum rotational position The

assembly is then clamped in place, with the adjustment apparatus preventing more than minimal movement during clamping in place. The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a sectional simplified isometric view of a slit lens assembly of the prior art, showing how it is used to receive light from a lamp and form it into a thin slit image at a film plane

Fig. 2 is a partial isometric view of a portion of a prior art projector, showing how the slit lens assembly of Fig 1 is held in a projector frame, while the slit of light is projected onto a film soundtrack and the output of a photocell is analyzed.

Fig. 3 is an isometric view showing the portion of the projector of Fig 2 and showing an adjustment device of the present invention Fig. 4 is a view taken on line 4-4 of Fig. 3.

Fig 5 is a view of a portion of the soundtrack of the film of Fig. 2, showing a slit of light in a proper orientation thereon, and also showing a slit of light angled from its proper orientation

Fig 6 is a front isometric view of the adjustment device of Fig 3, with a portion of a slit lens assembly shown in phantom lines

Fig 7 is a front elevation view of only the adjustment device of Fig 6

Fig 8 is a view taken on line 8-8 of Fig 7 Fig. 9 is a partial isometric view of the slit lens assembly clamp, showing the left side thereof

Fig. 10 is a left side elevation view of the clamp of Fig. 9, showing in phantom lines, how it is installed and removed DESCRIPTION OF THE PREFERRED EMBODIMENT

Fig 2 illustrates the sound head region 10 of a commercial 35mm theater motion picture projector 12 of the type that is currently in very wide use. The projector includes a slit lens assembly 14 which receives light from a lamp 16, and which directs an intense but very thin light beam at the soundtrack 20 of a motion picture film 22. The slit lens assembly 14 is clamped in place by a frame part 24 of the projector frame 26 of the projector. The frame part 24 includes a holder portion 104 that forms a largely cylindrical passageway 30 with two passages 32, 34 spaced along the axis 36 of the slit lens assembly 14 for holding the assembly. The projector frame portion 24 also forms a frame clamp apparatus or clamper 40 that can clamp the slit lens assembly 14 in position. The frame clamper 40 includes a semi-cylindrical strap portion 42 that is separated from the walls 32W, 34W of the passages by a pair of slits 44, the strap ending in a tab 46. A bolt 48 can be screwed in tightly to the rest of the frame portion to cause the strap portion 42 to push sidewardly against the slit lens assembly, to clamp it against opposite sides of the passages 32, 34.

Fig. 1 shows that the slit lens assembly 14 includes a largely cylindrical tubular housing 50 with a cylindrical main portion 49 and with a tapered front portion 51 that converges forward a slit image 60. The assembly also includes a slit member 52 lying within the housing and forming a slit 53 of small height, and various lenses such as 54, 56. The lenses direct light from the lamp 16 at the slit 53, and form an image of the slit at 60, onto the position of the soundtrack at the film plane 62 shown in Fig. 2. The slit image 60 has a very small thickness or height A, which is commonly a nominal height of 0.5 mil (1 mil equals one- thousandth inch or 0.127mm), and which is perhaps one-twentieth the height of the slit 53. Actually, the nominal slit image height A is 0.47 mil (0.119mm) in present commercial theater projectors (attained only if the slit image is precisely in focus).

It is important that the slit lens assembly be precisely positioned along its axis 36 so that the slit image 60 is in sharp focus at the film plane where the soundtrack lies. It is also important that the slit lens assembly be in a proper rotational position, indicated by arrows P, Q, about the axis 36, so the slit image 60 extends precisely perpendicular to the direction of movement M of the film by the projector film transport 63. Fig. 2 shows one method used to indicate the degree to which the slit lens assembly 14 is properly positioned along its axis 36 and in rotational orientation about its axis. A test film 22 is used, which contains high frequency sounds, such as at the desired maximum frequency of 12.5 kHz. A photocell 70 of the projector is already in place to detect light that has passed through the soundtrack. The output of the photocell

70 is amplified by an amplifier 72 (which may include an equalizer) and delivered to a test instrument 74 such as an oscilloscope and/or a frequency analyzer.

In previous methods for adjusting the slit lens assembly, the bolt 48 was loosened so the slit lens assembly 14 could be shifted in position.

With a skilled technician viewing the test instrument 74, the test film 22 was run through the projector, while the technician used his hand to grasp the housing of the slit lens assembly 14. The technician moved the assembly 14 slightly forward and rearward, until the high frequency output was of maximum amplitude. The technician then tightened the bolt 48 to clamp the slit lens assembly in position.

In practice, the technician found it very difficult to properly position the slit lens assembly. Since the height of the image 60 must be very small such as 0.5 mil (0.0127mm), the slit lens assembly had to be positioned along its axis 36 with high precision, with movements of thousandths of an inch (hundredths of a millimeter) having an important effect on the sharpness of the slit image. A rotation of the slit 53 of Fig. 1 , and consequently of the slit image 60 from a horizontal orientation that is precisely perpendicular to the direction of film movement M, affects the amplitude of the high frequency signals that can be obtained. Typically, a technician would rotate the slit lens assembly 14 slightly clockwise and counter-clockwise (Q and P) as well as shift it axially, as he attempted to obtain a maximum amplitude of the high frequency signals. A technician often would spend perhaps 15 minutes moving the slit lens assembly slightly back and forth and turning it until, in frustration, he settled on a position that was fairly close to optimum, or "good enough". Even then, when the technician tightened the bolt 48 to clamp the slit lens assembly in the selected position, the assembly shifted slightly during clamping, which could further affect the image 60.

When the prior format was used (film frames spaced by 4 perforations and a film speed of 18 inches per second, or 46cm per second), the fact that the slit image 60 was moderately out of focus and slightly angled from the horizontal, only moderately affected the high frequency response (up to 12.5 kHz). However, when a new format is used that results in a much lower film speed, a moderately out of focus slit image or a slit image angled moderately from the horizontal, can have a larger effect on high frequency response. Fig. 5 shows a section of a soundtrack 20 representing a high frequency tone of about 12.5 kHz.

Where the height B of the slit image 60 is 0.5 mil (0.0127mm), the slit image has a height that is about one-half wavelength of the high frequency tone (for a film speed of 62.5% to 78% of the current speed of 18 inches per second, or 46cm per second) The high frequency output of the photocell decreases rapidly as the height of the image 60 increases much past one-half wavelength of the recorded sound.

Fig. 5 also shows a slit image at 60A which is oriented at an angle C of 5° from the ideal orientation 60. In the particular example shown, the

12 5kHz tone is modulating a low frequency sound of low amplitude, so the opposite sides 80, 82 of the soundtrack are spaced about 6 mils (0.15mm) The angle C of 5° results in the opposite sides 80, 82 of the soundtrack canceling out each other so there is zero high frequency output. An angular deviation C of less than one degree is desirable to avoid significant cancellation under adverse conditions (high amplitude lower frequency, modulated by high frequency) Such low angular deviation has seldom been achieved in practice, and is especially important when the film speed is slow. In accordance with the present invention, applicant provides an adjustment device shown in Fig. 3 at 100 The adjustment device includes a holder clamp 102 which clamps to the holder portion 104 of the frame part 24, and a slit lens assembly clamp 106 which clamps to a cylindrical portion of the housing 50 of the slit lens assembly 14 The adjustment device also includes a lead screw 1 10 that connects the holder clamp 102 to the slit lens assembly clamp 106 The holder clamp 102 is clamped to the holder portion 104 by turning a holder clamp screw 112 on a clamp anvil 113. The slit lens assembly clamp 106 is clamped to the slit lens assembly 14 (at its projecting cylindrical front or rear 107, 109) by turning a rotation adjust and clamp screw 1 14 With the two clamps 102, 106 clamped in place, the lead screw 110 is tumed to advance the slit lens assembly 14 in forward and rearward directions F, R along the optical axis 36 of the slit lens assembly The technician does this until the optimum axial position is reached, which can be noted by the test instrument 74 of Fig. 2 indicating a maximum high frequency output.

After the optimum axial position is reached for the slit lens assembly, the technician moves the clamp screw 114 to turn the slit lens assembly 14 about its axis 36, in the directions P, Q. Such rotation of the slit lens assembly about the axis 36 is made until the test instrument 74 of Fig. 2 indicates that a (possibly higher) maximum high frequency response is again obtained. The clamp screw 114 is made with a long shank 115 (Fig. 7) so the screw handle 117 extends radially by a distance

N that is at least twice the diameter D of the slit lens assembly to enable finer adjustment in rotation. After the slit lens assembly is precisely positioned, the technician tightens the clamper bolt 48 (Fig. 3) to cause the strap portion 42 of the projector frame part, to tightly clamp the slit lens assembly in place, in both axial and rotational position. The adjustment device prevents large movement of the slit lens assembly, especially in the axial direction of axis 36, during clamping by turning the bolt 48.

As shown in Figs. 6 and 7, the slit lens assembly clamp 106 includes inner and outer parts 120, 122 that can rotate relative to each other about the axis 36, but that cannot move axially relative to each other. The inner part 120 has an aperture 123 (Fig. 9) of a size (0.75 inch or 19mm) for closely receiving the slit lens assembly, and has a threaded radially-extending hole 124 (Fig. 7). The rotation adjust and clamp screw 1 14 is threadably engaged with the hole 124, with an inner end 126 of the screw extending within the ring-shaped inner part to directly clamp to the cylindrical portion of the slit lens assembly housing 50. The screw extends through a slot 130 in the outer part 122. Thus, when the screw 1 14 is screwed in, it clamps to the slit lens assembly. Thereafter, the screw 1 14 can be moved in the directions P, Q to turn the slit lens assembly about its axis 36. The outer part 122 includes a collar 132 that is rotatably coupled to the shank 128 of the lead screw 110. As shown in Fig. 8, the lead screw is threadably engaged with threads of a hole 137 in the holder clamp 102, and has a portion lying in a hole 142 in the collar 132 but is not threadably engaged with the collar. Thus, when a handle 136 at the end of the lead screw is turned, the screw advances along the threaded hole 137 in the holder clamp, and thereby causes the slit lens assembly clamp 106 to be moved forward or rearward. The lead screw is formed with flanges 141 , 143 that prevent any axial movement of the lead screw with respect to the slit lens assembly clamp 106. A compression spring 140 extends between the slit lens assembly clamp 106 and an adjacent side of the holder clamp anvil 1 13 to take up any backlash in axial travel.

Fig. 7 shows that the slot 138 in the collar 132, through which the screw shank 128 extends, is about as wide as the shank of the lead screw, but is elongated in a direction radial to the axis 36. This allows the slit lens assembly clamp 106 to move radially (with respect to axis 36) but to not rotate about the lead screw, to fit different models of projector sound heads and to facilitate initial installation of the adjustment device 100.

Fig. 7 shows that the inner and outer parts 120, 122 are largely ring-shaped. However, the outer part 122 is formed with a gap 92. The gap 92 enables slight expansion of the outer part to assure that the inner part 120 can rotate relative to the outer part while being closely held against axial movement. Also, the gap 92 minimizes the width of the slit lens assembly clamp 106 in a horizontal direction, so that the left side of the clamp 106 can clear the adjacent part of the projector frame. The maximum largely horizontal distance M' of the left side of the clamp from the axis 36 of the slit lens assembly, is preferably no more than 150% of the radius D/2 of the slit lens assembly. It is possible to design the slit lens assembly clamp so the inner and outer parts are largely axially spaced instead of one lying completely within the other.

After the adjustment device 100 has been used to adjust the axial and angular positions of the slit lens assembly and the slit lens assembly has been clamped in place on the projector frame, the technician removes the adjustment device 100 from the projector. Thereafter, the adjustment device is carried away by the skilled technician, and preferably not left in the vicinity of the projector.

There is an advantage in having the adjustment device 100 provided as an apparatus that is temporarily mounted on the projector during adjustment of the position of the slit lens assembly, and thereafter removed. If an adjustment device were built into the projector, then a person operating the projector in a theater, might be tempted to adjust the position of the slit lens assembly himself, without the aid of the test equipment, which could lead to very poor sound. In addition, current projectors are expensive, and the ability to precisely adjust the position of the slit lens assembly without significant modification of the projector itself, or of the presently installed slit lens assembly, minimizes the cost for projector adjustment.

Figs. 9 and 10 show the construction of the left side of the slit lens assembly clamp 106, which facilitates its installation and removal. The sound head region 10 of the projector includes a sound drum with a rear surface 150 that supports the film and that lies substantially at the film plane 62. The sound drum surface 150 is spaced only a small distance of about one centimeter from the front end 152 of the tapered portion 51 of the slit lens assembly.

To facilitate removal of the clamp 106, both the inner and outer clamp parts 120, 122 are formed with cutouts 160, 162 that are tapered about 70° as seen in the side view of Fig 10. When the clamp 106 is moved forward to position 106A for removal, the tapered cutouts such as 160 are positioned at 160A to pass the tapered front end 51 of the slit lens assembly by sideward (rightward) movement of the clamp. This allows the clamp 106 to be installed and removed without scratching or interference from the close sound drum surface 150, or even with film in the projector The cutouts 160, 162 do not have to be tapered, although this minimizes the amount of material removed and stiffens the outer part 122 which has a gap. The sideward or lateral direction is indicated in Fig. 3 by arrow L. It is noted that applicant tried using an inner part 120 with a complete gap in it where the portion 170 lies However, it was found that when the rotation adjust and clamp screw 1 14 was tightened, the gapped inner part 120 expanded and locked to the outer part 122.

Applicant notes that he found that after the slit lens assembly was precisely positioned (axially and angularly) and continued to be held by the adjustment device, and the bolt 48 (Fig 3) of the clamper 42 was then tightened, that the slit lens assembly was turned by about 1 ° (but not moved axially) Applicant avoided an error by, after the optimum orientation was achieved, turning the slit lens assembly opposite to the direction that it would be turned by the clamper As a result, the slit lens assembly ended up in the proper orientation

Thus, the invention provides an apparatus and method for use with a current motion picture projector, which enables precision adjustment of the position of the slit lens assembly. The apparatus is an adjustment device that includes a holder clamp for clamping to the projector frame, a slit lens assembly clamp for clamping to the slit lens assembly, and a lead screw that extends between the clamps and that can be turned to precisely adjust the axial position of the slit lens assembly. The slit lens assembly clamp includes an outer or first clamp part that is directly connected to the lead screw, and an inner or second clamp part that is fixed to the slit lens assembly and that is rotatably mounted on the first clamp part. This allows the second clamp part to be turned about the axis of the slit assembly with respect to the first part, to change the angular orientation of the slit lens assembly. The apparatus is installed on a currently-used projector, with the projector clamp loosened, the position (axially and rotationally) of the slit lens assembly adjusted, the projector clamp tightened to fix the position of the slit lens assembly, and the adjustment device then removed from the projector.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.

Claims

WHAT IS CLAIMED IS

1. Apparatus for use with a motion picture projector that includes a projector frame (26) and a sound head region (10) with a sound head film plane (62), said projector having a film transport (63) for moving film through said sound head film plane, a light source (16) lying in said sound head region, and a slit lens assembly (14) lying in said sound head region and positioned to concentrate light from said lamp onto a sound track (20) location (60) on said film plane, wherein said projector frame includes a frame clamper (40) that can be loosened to enable movement of said slit lens assembly and which can be tightened to fix the position and orientation of said slit lens assembly, comprising a holder clamp (102) that is constructed to clamp to said projector frame; a slit lens assembly clamp (106) that is constructed to clamp to said slit lens assembly; a lead screw (110) that extends between said clamps, said lead screw being rotatably coupled to a first of said clamps so screw rotation does not advance said first clamp, and said lead screw being threadably coupled to a second of said clamps so screw rotation advances said second clamp with respect to said first clamp, whereby to avoid requiring direct hand adjustment of the slit lens assembly

2. The apparatus described in claim 1 wherein: said slit lens assembly has an axis (36) that passes through said sound track location on said film plane; said slit lens assembly clamp includes a first clamp part (122) that is directly connected to said lead screw in a connection that prevents relative axial movement of said first clamp part to said lead screw, and a second clamp part (120) that can be clamped to said slit lens assembly, said second clamp part being pivotable about said axis relevant to said first part but being resistant to movement along said axis or movement perpendicular to said axis relevant to said first clamp part, to enable only rotation of said slit lens assembly about said axis when said lead screw is not tumed.

3. The apparatus described in claim 2 wherein: said second clamp part lies within said first clamp part, said second clamp part includes a threaded hole (124) and a rotation adjust and clamp screw (114) that is threadably engaged with said threaded hole and that can be turned to advance it toward said slit lens assembly to clamp said second clamp part to the slit lens assembly.

4. The apparatus described in claim 1 wherein: said slit lens assembly clamp includes a largely ring-shaped inner part (120) that is substantially centered on said axis and that has a radially extending threaded hole (124), and a largely ring-shaped outer part (122) that lies around said inner part, with said inner part being rotatable about said axis on said outer part but restrained from axial movement relative to said outer part, said outer part having a slot (130) for receiving an assembly-engaging screw (114); said slit lens assembly clamp also includes an assembly-engaging screw (114) that projects through said slot in said outer part and that is threadably engaged with said threaded hole in said inner part, whereby the assembly-engaging screw can be tightened to fix said inner part to said slit lens assembly and said screw can be moved about said axis to turn said slit lens assembly about said axis.

5. The apparatus described in claim 1 wherein: said lead screw is threadably connected to only said holder clamp; said slit lens assembly clamp includes a collar (132) with a slot (138) that closely receives said lead screw and with flanges (136, 141) that prevent relative axial movement of said slit lens assembly to said lead screw; said slot being elongated in a direction that is substantial radial to

6. The apparatus described in claim 1 wherein said sound head film plane lies closely in front of the slit lens assembly and said slit lens assembly has a housing with a substantially cylindrical portion (49) and with a forward tapered front portion (51 ) that lies closest to said film plane, and wherein. said slit lens assembly clamp has a largely ring-shaped part (120) with a rear portion that has a cutout (160) lying on one side of said axis, with said cutout extending to the extreme rear end of the part, with said cutout being of a shape to allow said part to be moved laterally (L) off said slit lens assembly after said slit lens assembly clamp has been moved to a position (106A) forward but still surrounding the front end

(152) of said tapered front portion

7. The apparatus described in claim 1 wherein: said sound head film plane (62) extends primarily vertically and has a limited film plane region that is normally occupied by film, said light source (16) lies rearward of said film plane region, and said slit lens assembly (14) lies between said film plane region and said light source; said slit lens assembly clamp (106) lies forward of said holder clamp (102); said slit lens assembly has a largely cylindrical housing of predetermined radius (D/2); said slit lens assembly clamp has a first side that lies on a first horizontal side of said axis and that extends from said axis by a distance

(M') of no more than 150% of the radius (D/2) of said slit lens assembly.

8. Apparatus for use with a motion picture projector (12) than includes a projector frame (26) and a sound head region (10) with a sound head film plane (62), said projector having a transport (63) for moving film through said sound head film plane, a light source (16) lying in said sound head region, and a slit lens assembly (14) lying in said sound head region for concentrating light from said light source onto a slit-shaped area (60) on said film plane, with said slit lens assembly having an axis (36), wherein said projector frame includes a frame clamper (40) that can be loosened to enable movement of said slit lens assembly and which can be tightened to fix the position and orientation of said slit lens assembly, comprising: a slit lens assembly clamp (106) having first and second clamp parts (120, 122) wherein said second clamp part is constructed to clamp to said slit lens assembly and is rotatable about said axis on said first part; clamp means (102) for clamping to said projector frame and for attachment to said first clamp part to prevent rotation of said first clamp part about said axis and to limit movement of said first clamp part along said axis.

9. The apparatus described in claim 8 wherein: said first clamp part is in the form of a ring-shaped inner element (120) with an aperture of a size to closely surround said slit lens assembly and said clamp part has a screw (1 14) threadably engaged with said inner

element, with said screw having a handle radially spaced from said axis by at least the radius of said aperture.

10 A method for adjusting the position of a slit lens assembly (14) of a motion picture projector (12) along the axis (36) of the slit lens assembly, where the projector has a projector frame (26) with a frame clamper (40) that can be loosened to permit adjustment of the position of the slit lens assembly and that can be tightened to fix the position of the slit lens assembly, comprising: temporarily attaching aπ adjustment device (100) that includes first and second clamps (102, 106) and a lead screw (1 10) extending between them, where said screw is threadably connected to one of said clamps and only rotatably coupled but axially fixed with respect to the other of said clamps, including clamping said first clamp to said projector frame and clamping said second clamp to said slit lens assembly; directing light forwardly through said slit lens assembly and through a soundtrack plane (62) onto a photocell (70) while moving a film (22) with a soundtrack (20) containing a high frequency sound component of a plurality of kilohertz, so the soundtrack of the film continually moves past said soundtrack plane; analyzing the output of said photocell while turning said screw, when said frame clamper is loose, until a maximum high frequency response is obtained from said photocell; tightening said frame clamper, unclamping said first clamp from said projector frame, unclamping said second clamp from said slit lens assembly, and removing said adjustment device from said projector.

1 1. The method described in claim 10 including: after performing said step of turning said screw (110) until a first maximum high frequency response is obtained, performing the step of turning said second clamp (106) about said axis while continuing to move said film and analyze the output of said photocell until a second maximum high frequency response is obtained from said photocell which is at least equal to said first maximum high frequency response, all prior to tightening said frame clamper.

12. The method described in claim 1 1 including: after said second maximum high frequency response is obtained, slightly turning said second clamp (106) in an amount approximately equal but opposite to the amount that said slit lens assembly is tumed during tightening of said frame clamper.