US1551291A - Method and means eor making photographic negatives - Google Patents

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www@ .SR1 Q METHOD AND MEANS .FOR MAKING EHOTOGRAPHIC NEGATIVES V Filedmayee. 1925 2 sheets-sheet l y V l 1 V A. r

INVENTOR j Jfrwm ATTORNEY Aug. 25., 1925. 1,551,291

J. G. ,PMEVANS x METHOD AND MEANS FORMAK-NG PHOTOGRAPHIC NEGATIVES Filed' ze, 1925 2 sheets-shew 2 INVENTOR fg/@frans Patented Aug. 25, 1925:.

narran stares JEWETT G. Pfl- EVANS, F FORT WORTH, '.T.EXAS.`, l

mn'rnon `nani mms non mme rnoroenarnrc nnearrvns.

Application l'ed May 23, 1925. -Serlal No. 32,867.

' To all 'whom t may cof/wem:

'Be it known that I, Jnwn'rr G; P. EVANS, citizen ofthe United States of America, re-

. siding at Fort Worth, in the county of Tarrant and State of Texas, have invented certain new and useful Improvements in Meth-V ods andMeans for Making Photographic Negatives; of which the following is a speciticationlv I A This invention relates to new and useful improvements in method and means for making photographic negatives.

In the making of photographic plates for the production of half tonecuts the sensitized late is exposed through a screen so that t e plate when developed will depict the subject photographed by means of small squares called dots It has been found `vEthat some parts ofa subject photograph fastvariably the objects -appearing on the plate have more or less latness and particularly where a coarse screen, say of mesh, is used.

It is of course understood that light ra s as reflected? through a. lens range from t e highest white light, so called, to the lowest or darkest light or shadow. The range of tones intermediate vand including these extremes are known as gradations. `.These gradations each have a proportionate value one to the other and it will be readily-seen that the recording on a sensitized plate of one with a greater or less density than an other, woul produce over or under exposure, flatness and lack of detail or technique. In explaining my invention it is pointed out that it has particularly to do with the making of half tone negatives for photo engraving purposes in which the sensitized plate is exposed through a line screen. The relation of this screen to the sensitized plate has a controlling influence on the size ofA aperture used and it becomes necessar to -adjust the bellows and vary the size o the opening ofthe diaphragm for different subjects.

It has been found-by actual experience that the high or whitest lights which cause the largest dot on the negative, willA photoygraph to` perfection in size and opacity and while the lesser or darker tones causing the -smaller dots will photograph to the correct size, they will lack opacity which is necessary n order to produce a correct image of the subject photographed, and unless the small dots have the required opacity the plate when yprinted for etching purposesvwill permit too much light to pass through the -smaller dots, thuscausing flatness, lack of.

detail and a deviation from the original subl ject.

It is evident that Va dot lacking suiiicientopacity to make a print truly representative'of the value the dot is supposed to rep` resent, is defective. Therefore the object of my'invention is to produce dots on a sensi# ti zed late each having the required opacity and size to truly represent the tone value which it depicts.

The reason for the lackof opacity is that the whitest or highest lights or parts' of the subject, record or photograph in a given period, to a greater degree of opacity than the lower lights or darker parts of Athe subject, consequently if the time of. exposure 1s long enough to photograph the lesser lights or dark parts of the subject to secure the required opacity, then the high light dots `w1ll be exaggerated thereby giving an overexposed negative in the high lights., in

order to secure a correct exposure inf-"the" i lesser lights. K

It is evident that a large opening in the diaphragm will Vadmit a greater volume of light and also permit a greater spreading. of the light rays passing through the half tone screen, on account of greater angulation. It is also apparent 'that by reducing the volume of the reflected li ht rays which pass through the-lens, bv reducing the size' of the aperture in the diaphragm, the angulation or s reading of the dots on the plate is modu ated, whereby the high lights are retarded and the lower tones are intensified. From the foregoing it is evident that volume of light alone cannot spread the dots to their proper tone relations, but must be mechanically controlled to balance volume and angulation; the volume decreasing as the angulation increases and vice versa. The term angulation as used herein has reference to the angle of the light rays passing through the meshes of the half tone screen as controlled by the size of the diaphragm aperture and the extension of the camera bellows. Since angulation for the spreading-of th dots i's necessary and a greater period of exposure is required to form an opaque small dot from dark copy, as compared with a white copy; and also for the reason that the whitest or high li hts are reflected through the entire lens, an the lower or darker rays are reflected through the cntral ortion of the lens, means which will mo ulate the volume by admitting a greater volume of light through thecenter of the lens than through its margin, relatively during a given period, will permit the small dark dots to spread and photograph to the required opacity, without exaggerating the high light Vor large dots.

It has been' found that a diaphragm mounted to revolve and having an aperture shaped to admit light rays through its center during a major portion of the revolution and gradually diminishing in size toward the margin will give the results hereinbefore set fort A particular-object of the invention is tocarry out the photographing at a single exposure, which makes for a saving of time and expense and requires less skilled labor.-

A frequent fault in half tone cuts is the blurring or ragged-edges dots and it has been found in tests of my method using the same mesh of screen, that the dots are more pronounced and clean out and therefore a much higher grade of coarse mesh negatives, such as are used in newspaper work may be produced by my metho by an unskilled operator.

Means for carrying out the invention will be hereinafter set forth and shown in the accompan ing drawings, wherein:

Fig. 1 1s a longitudinal sectional .view of a compound lens constructed for' carrying out my improved method,

Fig. 2 is a diagram depicting the relative -transmission of light rays through the stop used with the lens, and

Fig. 3 isa diagrammatical view of the stop disk and its supports.

In the drawings the numeral 10 desig-y nates a lens housing having a flange 11 at its rear end by which it ma be fastened to, the front of the camera. T e housing has a vertical slot l2. In the housing are suitabl mounted the component members A, B, and D of compound lens, the members A .and B being in front of the slot and its members C and D in the rear thereof. The

center of the slot is co-incident with the' Vl have found by experiments, gives most satisfactory results when having the heart .shape shown, but I wish it expressly understood that the invention is notvt'o be limited to such a shape. The theory of the stop rom the top and opening shown is, that when the disk is per minute, the least restraint will be offered to the transmission of reflected light rays at the center of the disk which is axially alined with the longitudinal axis of the lens, and that the transmission will be proportionally retarded or restrained outwardly from said center in the ratio of the intensity of the light rays or tones.

A stop opening which extends on yboth sides of the center of the diaphragm and is bounded by a parabolic curve, has been found to give highly satisfactory results.

By referring to the diagram of Fig. 2 it will be seen that sixteen concentric. circles are shown intersecting the opening or aperture 16, said circlesfbeing equally spaced from the center. The segment formed in the smallest or central circle by the uncut portion 17 of the opening will obscure or interrupt less transmission of light than the segment in the next circle and so on out to the outer end of the opening, when said disk is revolved. Viewed converselythe inner circle will permit the greatest transmission of lightrays; while the outer circle will allow the least transmission of light rays. Therefore the disk in revolving will through its stop opening 16 restrain or retard the transmission of light rays proportionally to their intensity, thus distributing the-transmission radia 1y of the stop opening and affording a greater opportunity for the passage of the low li hts at the center than is "afforded the high ights at the outer end vof said opening, the intermediate tones `*being restrained in proportion to their relative value. The amplitude of the light rays controls their intensity and by varying the amplitude through restraint of transmission, the intensity 1s governed.

In operating thecamera the proper size of stop opening is determined in the usual manner well known in this art; the motor.

is started and the disk 13 having the proper size of stop opening 16 is drop ed into the slot 12 upon the rollers 14. rlhe late is placed and the exposure is made w ile the 'revolved at about one hundred revolutions diskv is revolving. A single exposure is all that is required and such an exposure does not require nearly as much time asthe three ing a continuously rotated apertured diaexposures which are usually made in photo.-

`en gravin plants.

What claim,l is:l i 1. A device for lcontrolling the transmission of light rays through a. lens comprisphragm in Constant operative relation for interrupting the passage of said rays according to their reiiected intensity, whereby the rays of varying intensity are recorded .z which theyd pass.

in their proportional values.

2. A device for' controlling the transmission of light rays through a lens comprising a continuously rotated apertured diaphragm for admitting a maximum passage of light rays through the center of thelens and diminishing radially of the lens the proportionate passage of light rays therethrough.

3. The methodof controlling the'passage 'of reflected light rays from a subject .through a lens which consists in making a single exposure through ardiaphragm continuously rotated during exposure and having an aperture for controlling the period of transition ofthe reflected rays of light from the respective parts of the subject according to the portion`of the 'lens through 4. exposure diaphragm for a camera having an aperture extending on both sides of the center thereof and diminishing in area toward its outer- 'end and means for continuously rotating said diaphragmdurmg exposure.

5. The combination with a photographic lens of a diaphragm contnuouslyrotated during exposure and having an eccentric aperture having 1ts greatest area at the center of the diaphragm. l f

6. A device for controlling the transmis- Sarplisliilay' threughlensgiomprising a diaphragm having an aperturfatwthe focnaceter ot the lens having its W'alls ex- Y tending upon a lparabolic curve to each side .of said focal center and means for con- :sol

8. A device forcontrolling the transmission of light rays through a lens comprising a disk continuously rotated during exposure and having an aperture with walls extending radially and eccentrically to the'A ocalcenter of said lens.

9. A device for controllingthe transmission-of light rays through a. lens comprising a disk continuously rotated during exposure and having fa' substantially' heartshaped aperture disposed with its base at the focal center of the lens. 4

sion of light rays'througha lens comprisi ing a disk continuously rotated during ex- -posure and having a substantially heartshaped-aperture disposed with its base at the focal center of the lens, al casing comprising opposite lens carrying members spaced apart, a-rdriving member between said members upon which the disk is' supported,l and- 'meansfor rotating said member.

ture..

JEWETT G. P. EVANS.

In ytestimony whereof I'afx my signa- 70 10. A device for controlling the transmisf

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