Moving Picture World (Nov-Dec 1924)

2S0 MOV IN i PICTURE WORLD Bargains in used Pipe Organs, Etc. At from one-fourth original price and up, taken in exchange on new Page Organs. 1 Style 75 Robert Morton Organ, both band and roll console 1 Style 50 Fotoplayer 1 “ 45 1 “ 41 1 “ 35 1 “ 30 1 M 20 One Marsh Organ and Piano One Votler Holcamp Organ One Style G Wurlitzer One Style R “ One Style O “ One Link Organ and Piano 5 Mills Violana Virtuoso’s Many Others The Page Organ Company Lima, Ohio SPECIAL ROLL TICKETS Your own special Ticket, any colors, accurately numbered : every roll guaranteed. Coupon Tickets for Prize Drawings: 5.000 for $7.00. Prompt shipments. Cash with the order. ’ Get the samples. Send diagram for Reserved S'eat Coupon Tickets, serial or dated. All tickets must conform to Government regulation and bear established of admission and tax paid. SPECIAL TICKET PRICES Five Thousand $3.50 Ten Thousand 6.00 Fifteen Thousand 7.00 Twenty-five Thousand 9.00 Fifty Thousand 12.50 One Hundred Thousand 18.00 National Ticket Co. Shamokin, pa. ROLL — Machine — Coupon TICKETS QUALITY — Second to nonel SERVICE Unexcelled — our LOWEST PRICES will be mailed to you on request. State your requirements by mail — Today I TRIMOUNT PRESS LARGEST AMUSEMENT TICKET PRINTERS IN NEW ENGLAND FOR 17 YEARS. 119 ALBANY ST., BOSTON, MASS. Motion Picture Cameras and the World’s largest market of second hand and new instruments, priced from $50.00 up. Send for big catalogue and bargain list. BASS CAMERA COMPANY 109 NORTH DEARBORN CHICAGO Some Suggestions Chauncey L. Greene, Minneapolis, writes at some length, but interestingly, as follows : The scheme I proposed for re-grinding the pitted surfaces of collector lenses was really the idea of my very good friend O. S. Keay, of this city. The price of one dollar for resurfacing, suggested by me, is what we pay here in Minneapolis for the work, which is done by a local spectacle firm. As I said, Mr. Keay is my friend, but if we ever met without an argument it is so long ago we have both forgotten it. Keay is a projectionist. His equipment consists of two Power projectors and a “Rexolux” single arc motor generator. Change-over is made by ‘stealing* the current, hence the collector lenses pit very rapidly. When he installed Cinephor the condition was made worse, due to the relatively short crater distance. He and I discussed the matter several times. I was strong for a glass baffle plate, such as Bausch and Lomb now propose (which, by the way, was suggested by John Griffith, in this department a long while ago. — Ed.), while he was for re-surfacing the lenses. That was last November. The collector lens surfaces have been reground twice since then, and seem good for two more surfacings. One of them has cracked. It started with a very tiny crack in the center of the lens — the collector and converging lenses are NOT in contact — and gradually increased until in two or three weeks the crack reached the edge on one side and nearly to the edge on the other. The Pin-Hole Idea In August 23rd issue there was further discussion of the “rear of the lamphouse pin hole’’ idea. Why not put a dark observation window in the rear wall of the lamphouse and look directly at the reflection of the crater face on the face of the collector lens? If the window be so placed that the line of sight passes as nearly as may be to the edge of the crater there will be no trouble from multiple images. Aspheric Mirrors? Perhaps it is not quite the thing for me to fail to mention a thing at the proper time and then, long after, cut in. However, the answer of Brother Bennewitz to question 83, August 30 issue, seems to me to be incorrect as to its third section, wherein he says the reflecting arc mirror is spherical. All the reflecting arc mirrors (American Reflecting Arc) I have examined have been aspherical mirrors of 2.25 in. focal length, which is the reason for the wonderful quality of light from the reflecting arc lamp. There is practically no spherical aberration, and there can be no chromatic aberration in such mirrors. The resultant beam very closely approaches the ideal, or theoretically perfect condition, and mathematical theory can be advantageously applied. I shall now describe the method I use for setting up the reflecting arc, in the hope that it may prove useful until such time as Griffith has a chart prepared for us. Setting Up Reflecting Arc First I chuck a block of wood in a lathe and tack a piece of sheet metal to it. I then drill a hole about 1/64" with a drill held in the tailstock chuck. If no tailstock is available, press the dead center against the metal while lathe is running, and then drill with a hand drill in the center thus made. Next put In back gears, and with a tool having a slender point commence scribing a circle In the metal the exact inside diameter of the projection lens mount. A good stunt is to get a junk lens mount and make the thing permanently. Advance the tool until the metal Is cut through. Place this sight plate in the projection lenfs mount and mount the lens in the projector in the usual way. (Evidently what he means is to either obtain a duplicate lens barrel, or to remove the lens cells from your regular projection lens barrel. — Ed.) Arrange two threads diagonally across the aperture (from corner to corner. — Ed.) Line up the jaws of the lamp with each other by clamping one perfectly straight carbon November 15. 1924 in both jaws. (A straight carbon may be selected by rolling carbons on a perfectly flat 1 surface. — Ed.) After lining the jaws, remove the carbon and mount the lamp in the lamphouse and so adjust it that when looking through the sight plate in the lens barrel the cross threads will center exactly in both posi | tive and negative carbon holders. After J clamping the lamp in place the negative car' j bon may be lowered the required amount to f cause the crater to burn correctly. When this is done remove threads and sight plate and replace the lens cells, or if . you use a dummy lens for the purpose, then replace the projection lens in its mount.” ' For Griffith Friend Green then continues with the following, which is respectfully passed along to Griffith and the other optical sharks. He says : Call distance from crater to mirror X, distance from mirror to crater image Y and focal length of mirror F. From the optical III theory — -I = — . Call the ratio of crater im ■' X Y F age diameter to crater diameter R. This is also the ratio of Y to X. That is to say y Y=RX. Crater image diameter equals the diameter of the rear factor of the projection lens, and Y equals distance from mirror to lens. The 1 idea is to just fill the rear factor of the pro j jection lens with the crater image, since that is smallest part (diameter) of the light beam, 1 and the larger it is the less will be the dis 1 tance from crater to mirror. Even in ex I treme conditions breakage of mirrors seems j to be negligible, or at least that has been 1 mv experience, even using 35 to 40 amperes. ] We then have: I I I X RX F R I I RX RX F R+I I RX F Multiply both sides of this equation by (R + I) F XF and it becomes = X, which Is the j R distance crater should be from the mirror. 1 RX is the distance mirror should be from the rear factor of the projection lens. Spot adjustments are made with the mir ‘ ror, NOT by moving the lamp. Crater diame ■ ter may be obtained beforehand by assum , ing a conservative utilization factor of 100 lumens per ampere and measuring craters at the need current value on the smallest carbon which will carry the current, taking an average of three or four trials on as many different carbons. Phew! That’s all “yourn” Griffith, and I wish you every joy with it. I’ve just returned from a month’s absence and a couple of bushel baskets of letters literally scream for attention, therefore I can’t stop to dig out the why and wherefore of all that X times Y business, which probably is allright and of genuine value. As to the plan for lining the optical system, it is effective, but I believe a more simple and just as effective way is to secure a perfectly straight round steel rod of sufficient length, testing its perfect straightness by rolling it on a surface you have tested for flatness with an ordinary carpenter’s square. Remove the lens cells from the projection lens, open the projector film gate. Pass the rod through the lens barrel and projector aperture and on into the lamphouse, clamping its end into BOTH carbon jaws, so aligning them that they fit the rod perfectly. Then so adjust the lamp that the rod is EXACTLY central in both projector aperture and projection lens barrel. But at that I'm not so certain but that Greene’s method is better and more accurate. Anyhow there (Continued on following page)