US1404440A

US1404440A - Focusing device

Info

Publication number: US1404440A
Application number: US410664A
Authority: US
Inventors: August F Jobke
Original assignee: Individual
Current assignee: Individual
Priority date: 1920-09-16
Filing date: 1920-09-16
Publication date: 1922-01-24
Anticipated expiration: 1939-01-24

Description

A. F. JOBKE.

FOCUSING DEVICE.

APPLICATlON FILED SEPT. 16, 1920.

1,404,440. Patented Jan. 24-, 1922.

B "G 5/ r ,7 i s G D A INVENTOPI UNITED STATES PATENT OFFICE.

AUGUST 1. JOB, 0F PI'JI'IJSBURGH PENNSYLVANIA.

rocusme DEVICE.

Application filed Sptember 16, 1920. Serial No. 410,664.

To all whom it may concern:

Be it known that I, AUGUST F. J claim, a citizen of the United States, residing at Pittsbur h, in'the county of Allegheny and State of%ennsylvania,have invented a new and useful Focusin' Device, ofwhich the following is a speci cation.

My invention relates'to a focusing device, the object of which is to automatically keep a photographic lens, a plane surface corresponding to an object to be projected and a plane surface corresponding to a screen-or projecting surface in such posltlons relative to one another, that the image produced through the lens" is sharp at any ratio of magnification as well'as reduction.

Another object of this invention is, to

make it adjustable to such an extent as to render it applicable not only to the use of a single lens of a certain focal length, but to the focal length of any other lens chosen, thus giving it a usefulness highly desirable in all kinds of reproduction, and facilitating its manufacture, since a single model may lengths.

In the common way of reproduction it is very diflicult to get a perfectly sharp image and practically impossible, if a weak light source is used, the reproduction is nearly to the same size, or if the negative happens to be dense. 'In subh cases one "can improve results 'by stopping the lens down, which has the disadvantage of requiring a longer exposure. This device is to overcome these disadvantages, allowing the use of a full lens opening, thus permitting much faster work. i

' Being of a very simple construction, based on a simple geometric configuration, this invention permits an exact adjustment of its several elements, and therefore perfectly accurate results can be obtained through its application. attain these objects by applying a mechanism, the principal part of which is a straight lever, and I use the'angular posisition of this lever relative to the optical axis of the combination to establish both conjugate focal distances.

fully disclosed and made understood in the cover along range'of different focal following description, Where reference is had to the drawing, in which:

Figure 1. is a configuration intended to explain geometrically the relations existing Between the different parts of my inven- Figure 2 is a diagrammatic view of the focusing device applied to the elements of an optical" combination. i Since this invention permits a broad application. and will find varied uses in the field of optical projection, I'shall not descrlbe it in connection with specific apparatus, but refer only to those elements which are necessary to project an image through a lens.

In explaining the working of this focusmg device I refer to Figure 1, in which A E 1s a rectangular triangle and GDC a right angle, the arms of which are arallel to the catheti of the triangle. The ypothenuse AE may be movable angularly about D as its fulcrum. It can be shown, that AGzGDzDGzGE, or' A,G:GD=DG:GE,. Ife we select GDzDCzthe focal length of a lens, the two dimensions AG and CE or A G and CE are'reciprocals to each other as factors of the focal length; in other SpecificationofLefterslafent- Patented Jan. 24, 1922. v

words, they are equivalents of extrafocal the hy'pothenuse determines the ratioof the corres onding projection. If the angle at A or is 45, then the rojection is of the ratio=1, and assuming t at A be the position of the projecting surface andE that of the object to be projected, an angle at 'A smallerthan 45 corresponds to enlargin while an angle larger than 45 correspon s to reduction; Generallyspeaking, the tangent of the angle at E is the factor of projection for E as the object.

Figure 2 shows an optical combination as usedby photo-engravers to obtain a reversed negative with a sensitive plat'e'in the normal position, or a right-faced negative may be obtained in placing'the sensitive plate in a reversed position. This combination consists of a plane surface at A, re'presenting an object to be projected, a lens B, equipped with a prism or reflector R, and

in the ratio of 1 2 and the leverin the posia plane surface H representing an easel or sensitive medium. The reflector R turns the optical axis AB through 90. Since the central point of reflection is at R, instead of the optical center B, the conju ate focal distance is BH plus RB (or R and the bracket W is to provide .the second member to have BEzthe conjugate focal distance.

A straight lever AE, adapted to be mov able angularly about its fulcrum D, which isv located one focal length from a line AB, garallel to the optical axis, and from a line E, normal thereto, slides in pivoted bearings A and E, which are movable on the lines mentioned. -Any angular motion of this lever will produce conjugate focal lengths AB and BE, or A B and BE respectively.

In order to vary the arrangement for a different focal length, the fulcrum D is mounted upon a nut, sliding in a slot placed at 45 to the lines AB and BE and adjusted by means of the screw L, which for convenient, handling hasthe thumbhead M. The equal focal distance ofany point D from AB and BE is therefore always maintained. If the projection from A to H is tion of the fulcrum at D is kept parallel to AE, it can easily be seen, that the ratio of projection must be the same since the triangle, A BE is similar to ABE. The plane I-I-will be removed'to the position H since EH is equal to the corresponding major focal distance.

The application of a movable fulcrum as shown is olf greatest commercial importance, since the exact focal length of a lens may not be given, or only assumed to be of a certain magnitude. t would be commercially impossible to manufacture a focusing device for every focal length used in prac tice, since every style of lens has a different focal length, eventually varying little from a similar competing one. In varying the position of the fulcrum of the lever, it can be adjusted to a great range of lenses and a sha a image always be secured.

ile AE is the position of the lever fol a projection of 1:2, which in this case is magnification, the opposite, i. e., reduction of 2:1 will be secured with the osition A,E The position of the plane in H, will result then in the conjugate focal distance BA,=2BE,.

In the description of this arrangement it must be understood, that the locations of the difierent parts given are ideal ones,

ivin'g the simplest formof combination.

ny changes of positions relative to the center lines of the lens must be made up by additional members or a change in dimensions of those used, and since the arrangement shown is only one o'f those. possible to use, I declare such variations as being within the scope of my invention.

What I claim and desire to secure by Letters Patent, is:

1. In a focusing device a lens and a reflector adapted to reflect a ray of light through the optical axis at 90, a plane representin an object to be projected and a plane adapted to receive an image therefrom located at conjugate focal distances from the optical center of the lens, a straight lever movable-about a fulcrum located one focal length of the said lens from two lines parallel to the two branches of the optical axis and adapted to out both lines at conjugate focal distances from the point of their intersection, and means to move the said two planes simultaneously with the points of intersection of the lever and the said" lines.

2. In a focusing device a lens and a refiector adapted to reflect a ray of light through the optical axis at 90, a plane representing an object to be projected and a plane adapted to receive an image therefrom located at conjugate focal distances from the optical center of the lens, a straight lever movable abouta fulcrum located one focal length of the said lens from two lines parallel to thetwo branches of the optical axis, two pivoted bearings sliding on the arms of the said lever and along the said two lines, their centers establishing conj'ugate lfocal distances on the two lines from the point of their intersection, and means to move the said two planes simultaneously with the said pivoted bearings.

3. In a focusing device a lens and a reflector adapted to reflect a ray of light through the optical axis at 90, a plane representing an object to be projected and a plane adapted to receive an image therefrom located at conjugate focal distances from the optical center of the lens, a straight lever movable about a fulcrum located one focal length .of the said lens from two lines parallel .to the two branches of the optical axis, the fulcrum being adjustable along a line of 45 between the said lines and from the point of their intersection, two pivoted bearings sliding on the arms of the said lever and along the said lines, their centers establishing conjugate focal distances on the said lines from the point of their intersection, and means to move the said two planes simultaneously with the said two pivoted bearings.

4. In a focusing device a lens and a reflector adapted to reflect a ray of light through the optical axis at 90, a. plane representing an object to be projected and a plane adapted to recewe an image therefrom located at conjugate focal distances from the optical center of the lens, a straight lever movable about a fulcrum located one 189 {focal length of the said lens from two lines parallel to the two'branches of the optical axis, the fulcrum being adjustable along a line at 45 between the said lines and from the point of their intersection, two pivoted bearings sliding onthe arms of the said lever and along thesaid lines, their centers establishing conjugate focal distances on the said lines from the point of their intei'section, means to move the said two planes 10 l simultaneously with the said two pivoted bearings, and means to change the position of the fulcrum to suit lenses of different focal lengths.

In testimony whereof I afiix my signature. 15

AUGUST F. J OBKE.