Transactions of the Society of Motion Picture Engineers (1916)

Record Details:

Something wrong or inaccurate about this page? Let us Know!

Thanks for helping us continually improve the quality of the Lantern search engine for all of our users! We have millions of scanned pages, so user reports are incredibly helpful for us to identify places where we can improve and update the metadata.

Please describe the issue below, and click "Submit" to send your comments to our team! If you'd prefer, you can also send us an email to mhdl@commarts.wisc.edu with your comments.




We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.

Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.

the axis by corresponding chief-rays on the object side and the image side of the objective, and N is the reduction factor. The "tangent condition," as it is generally known, is precisely fulfilled in the case of symmetrical objectives^ for one pair of conjugate positions of the object and image, i. e.^ in the case of unit magnification, and freedom from distortion may be realized for certain other positions of the object by also correcting a symmetrical objective spherically with respect to the position of the diaphragm and its images— the entrance and exit-pupils {Bow-Sutton condition.) Orthoscopy is not completely realized for any distance of the object by unsymmetrical objectives, however, and with respect to correction for distortion most of the modern anastigmatic objectives show about the same amount of positive distortion as the Petzval type projection objective. This is not a matter of such moment in every-day motion picture projection as it is in photographic reproduction work, for in less than one theatre out of every hundred is the center of the screen co-axial with the projector optical system, or the entire screen perfectly perpendicular to the axis of projection. Inasmuch as operators, theatre managers and architects have failed in the majority of cases to provide for an orthoscopic representation on the projection screen, it can be claimed that the distortion errors due to conditions prevailing in the majority of theatres far transcend the amount of distortion to be found in the images produced by any of the modern types of objectives, when they are used for projecting upon a screen placed truly perpendicular to the axis of projection. (Note — For convenience I have created the expression ''axis of projection' which is defined as the prolongation of the axis of the projector optical system {assumed to be in perfect alignment) as a straight line to the projection screen. I suggest that this definition be adopted by the Society and included in the Society's list of Motion Picture nomenclature). As all of the modern anastigmatic objectives having a large aperture are of unsymmetrical construction, they exhibit about the same amount of distortion as to Petzval objective at angles up to io° from the axis, but there is one notable exception to this statement — the objective in question being the I C Zeiss Tessar of/ 3.5 aperture ratio. In this objective, which has previously been recommended as eminently suitable for projecting purposes, distortion has been reduced to an almost negligible quantity at 10° away from the axis, which is quite remarkable considering the large aperture. I have not been able to examine one of the recent Cooke anastigmatic projection objectives which are said to work at/ 2. and I cannot therefore report upon it with respect to distortion, but the Cooke objectives of smaller effective aperture are very well freed from distortion, thus indicating the possibilities of securing a good correction in this respect for the Cooke objectives of larger aperture. A final advantage which can be claimed for the modern types of photographic objectives, when used in motion picture projection, is their compact construction, which permits a very efficient utilization of the available light source.