DOCSLIB.ORG

Sources of Error in and Calibration of the F-Number of Photographic Lenses by Francis E

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Sources of Error in and Calibration of the F-Number of Photographic Lenses by Francis E U. S. Department of Commerce Research Paper RP1927 National Bureau of Standards Volume 41, October 1948 Part of the Journal of Research of the National Bureau of Standards Sources of Error in and Calibration of the f-Number of Photographic Lenses By Francis E. Washer In problems of photography, where the accuracy of lens marking is critical in determin­ ing the proper exposure, the various errors to which these markings are subject is of con­ sid erable in terest. The present report gives the magnitude of such errors that were found to exist in a representative group of 20 le nses having focal lengths that range from 0.5 to 47.5 i,l. In addition, the resul ts of calibration of these lenses by a photometri c method that permits compensation of light losses resulting from absorption, refl ection, and scattering are given. Value of lens transmi ttance for these lenses are shown . A mcthod of p lottin g results of nominal, true, and calibrated I -number is g iven tha t permits quick evaluation of t he magni tude of the over-a ll error in terms of fractions of a stop . I. Introduction McRae [9] and by Gardner [1, 2], who proposed With the advance of photographic technology, several possible methods for calibration of a len . a need has developed for more precise information In the present article, one of the methods described on the light-transmitting characteri tics of photo­ by Gardner is verifi ed experimentally. The ex­ graphic objective . In particular, a specific need perimental technique is de cribed, and the varia­ exists for a more accurate means of marking or tion in performance for 20 lenses, having fo cal calibrating the len es that employ a variable stop lengths that range from 0.5 to 47 .5 in., are shown. for adjusting the len speed. The usual method, Attention is given to som-ces of O1 r01' in the exi t­ at present, of calibrating a lens is to inscribe a ing marked j -n umber. Lastly, a process is de­ scale of j -numbers on the diaphragm control. scribed for determining the transmittance of a The ej-number are based upon certain geometric lens from data obtained in the course of calibration. properties of the len , and neglecting errors of marking, provide a satisfactory means of varying II. Apparatus a,nd Method of the speed of the particular lens by definite integral Measurement step.. Unfortunately this system of marking take no cognizance of differences in light-trans­ The apparatu consi ts essentially of a broad mitting properties that occur among different uniform souree of white light, a sensitive light­ types of lenses and, in addition, those differences mea uring device, and a holder that can be used that result between lenses of the same type when interchangeably for either mounting the len the surfaces of one have been treated to reduce under test or one of a series of standard diaphragms refl ection 10 ses. each of which has a centrally located circular This problem has been under vigorous attack opening of known diameter. The arrangements for the past 10 years and numerous methods of these clements is the same as that suggested by [1 to 12] 1 have been devised for the rating of lens Gardner [1 ,2] . The relative lens speed is deter­ speed with re pect to some standard. These mined by a comparison of the quantity of light methods differ in such matters as type of light flux transmitted by a lens with that transmitted source, comparison lens or standard aperture, and by a 'circular opening. By making an appropriate type of light-registering device. The theoretical series of measurements and by proper interpreta­ a pects of the problem have been discu ed by tion of their significance, the lens can be calibrated in terms of an "ideal" lens having 100-percent 1 Figures in brackets indicate the literature references at the end of tbis pa~er. transmi t tan ce. Calibration of I-Numbers 301 1. Procedure for a Lens minimize error, two sets of data are taken for both A lens in mounted in the holder, and its axis is the lens and the series of standard diaphragms, so alined with the center of the broad uniform source intermingled that random fluctuations in the and the center of the small circular opening in the brightness of the light source and in the sensitivity baffle covering the sensitive element of the light­ of the light meter can be neglected. measuring device. The front of the lens faces the Ideally, the diameters of the standard dia­ light source, and the distance separating the rear phragm openings should be so chosen that the nodal point of the lens and the baffle covering the same series of f -numbers are present in both light sensitive element is adjusted to equality, phases of the experiment. Too, the distance, D , with the equivalent focal length, F, of the lens. should equal the equivalent focal length, F; of the Thfl opening in the baffl':) does not usuallv exceed lens. In practice, however, it has proved to be 1 mm, except for some lenses of very l;ng focal more convenient to letD differ fromF and to place length, in which cases it is kept under O.OlF. more reliance upon the ratio, DIA, where A is the All parts of the equipment are shielded so that diameter of the circular opening in a standard only light from the source that passes through the diaphragm. When a wide ' variety of lenses are lens can reach the light-sensitive element. being calibrated, as is the case in this experiment, Readings of the light meter are taken at each of it is simpler to compute the f-number of the stand­ the marked stop openings. To mllllmlze error ard diaphragm from the ratio, DIA, and to deter­ arising from back lash, readings are taken both mine the performance of the conventional series for the condition of the setting at the marked off-numbers from the curve of light meter reading f-number being made with the diaphragm ring of versus f -number than to attempt to reproduce the the lens moving in the closing direction and with conventional set of f-numbers by appropriate the diaphragm ring moving in the opening direc­ selection of values of D and A. tion.2 The readings from these two sets of obser­ The f-number for a lens is defined by the equa­ vations are averaged, and this value is taken as the tion 1 accepted reading of the light meter at a given f - number= -2- ' - , (1) marked stop opening. SIn a 2. Procedure for the standard diaphragms where a is the angle between the axis and the ex­ treme ray of the circular conical bundle transmitted The lens is replaced by one of the series of by the lens. In the case of the standard dia­ standard diaphragms, which have centrally located phragm, the relation connecting the measured circular openings with known diameters. The quantities D and A is reading of the light meter is taken, and the dis­ tance D, from the diaphragm to the baffle covering 1 D (2) the light-sensitive element is measured. This A 2 tan a' operation is repeated for several of the standard diaphragms so selected that readings of the light Accordingly, the values of the f -numbers for the meter are obtained throughout the same range of standard diaphragms can readily be computed readings that were observed for the various from the known values of DIA. A sufficiently marked apertures of the lens. The brightness accurate determination of the f -number can be of the source and the sensitivity of the light meter made with the aid of a curve, such as is shown in are kept unchanged throughout both parts of the figure 1. To produce this curve, the values of experiment. To insure constancy of brightness of the quantity, f-number -DIA, are plotted as a the source, a constant voltage transformer is fupction of DIA. Hence, for a given value of used to maintain a constant voltage for the lamps DIA, the increment that must be added thereto tu that illuminate the broad uniform source. To yield the f-number can be easily read from the graph. For values of DIA greater than 15, the , Ten lenses (10, and 12 to 20, incl.) were calibrated in this manner. 'l' he remaining 10 lenses were calibrated witb the diaphragm ring moving in the values of DIA and f -number are equal for all closing direction only in accordance with the recommendation contained in practical purposes, since their difference is less than Report No.6 of the Snbcommittee on Lens Calibration of the Society of Mo­ tion Picture Engineers on Nov. 6, 1947. 0.1 percent. 302 Journal of Research .14 of Lbe ligh t meter and the j -numbers of an ideal len. Z I n a like manner, the valu es of the scale defl ec­ .I 0 tion of the li gh t meter are plotted against the j ­ ,C( o number of the acLual lens on the same curve I .0 8 \ sheet. The resulting curve, des ignated curve 2 tt: w CD in fi g ~ll' e 2, is a straigh t line parallel to curve 1, 6 \ ~ .0 Z, but displaced laterally therefrom. This displace­ LL .04 \ ment shows in a striking manner the effect of li ght losses in the actual lens.
Load more

Recommended publications
  • Reveni Labs Light Meter User Manual and Operating Instructions Revision: 4 Date: 2020-04-16
    Reveni Labs Light Meter User Manual and Operating Instructions Revision: 4 Date: 2020-04-16 Revision: 4 – 2020-04-16 Layout and Features Key Features • Ambient reflective metering • Single LR44 battery • Integrated flash/accessory • EV Display feature shoe mount • 45-degree cone sensor field • Bright and crisp OLED of view display • Left and right lanyard/strap • Simple controls and menu holes • Aperture or Shutter priority • Dimensions: 0.92(22.5) x mode 0.86(21.8) x 0.71(17.8) • Exposure compensation in inches(mm) 1/3 stops (-2 to +2 stop • Weight: 9g incl. battery range) Technical Data • Shutter speed range 1hr – 1/8000th sec in 1 stop • Aperture range increments • Film ISO range F0.7 – f1024 in 1 stop increments ISO 1 – ISO 12800, see “Setting Film ISO” for full list • EV Range: EV 2 – EV 19.5 in 0.1EV increments (@ISO 100) Page 2 of 14 Revision: 4 – 2020-04-16 Getting familiar with your meter The Reveni Labs Light Meter is intended for easy attachment to the top of a camera via the flash/accessory “hot/cold” shoe mount. This is a common feature on top of many cameras made in the past 100 years. The precise dimensions of the shoe vary from camera to camera so if initially if the fit of your meter is tight, it will “wear” slightly over the first several uses and become more free-moving. This is not a problem as there are integrated lever springs to ensure the meter does not fall out of the camera mount.
    [Show full text]
  • Ground-Based Photographic Monitoring
    United States Department of Agriculture Ground-Based Forest Service Pacific Northwest Research Station Photographic General Technical Report PNW-GTR-503 Monitoring May 2001 Frederick C. Hall Author Frederick C. Hall is senior plant ecologist, U.S. Department of Agriculture, Forest Service, Pacific Northwest Region, Natural Resources, P.O. Box 3623, Portland, Oregon 97208-3623. Paper prepared in cooperation with the Pacific Northwest Region. Abstract Hall, Frederick C. 2001 Ground-based photographic monitoring. Gen. Tech. Rep. PNW-GTR-503. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 340 p. Land management professionals (foresters, wildlife biologists, range managers, and land managers such as ranchers and forest land owners) often have need to evaluate their management activities. Photographic monitoring is a fast, simple, and effective way to determine if changes made to an area have been successful. Ground-based photo monitoring means using photographs taken at a specific site to monitor conditions or change. It may be divided into two systems: (1) comparison photos, whereby a photograph is used to compare a known condition with field conditions to estimate some parameter of the field condition; and (2) repeat photo- graphs, whereby several pictures are taken of the same tract of ground over time to detect change. Comparison systems deal with fuel loading, herbage utilization, and public reaction to scenery. Repeat photography is discussed in relation to land- scape, remote, and site-specific systems. Critical attributes of repeat photography are (1) maps to find the sampling location and of the photo monitoring layout; (2) documentation of the monitoring system to include purpose, camera and film, w e a t h e r, season, sampling technique, and equipment; and (3) precise replication of photographs.
    [Show full text]
  • Tip Sheet – Lumen Meter
    TIP SHEET – LUMEN METER What is a lumen meter? A light meter or lumen meter is a device used to measure the amount of light in a certain area. Lumen meters have many uses such as photography and cinematography, however for our purpose we want to help reduce the amount of wasted light which equals wasted electricity. If conducting an outdoor lighting audit the purpose of a lumen meter would be to reduce the amount of light pollution. Light output is typically measured in luxes or lumens. Sometimes you will hear the word footcandles. This is another standard unit of measure that is used interchangeablely with the term lumen. Ehow.com defines a lux as a uniform standard by which the amount of visible light present in a given space can be described where as a lumen is a measure of just how much visible light is produced by an object such as, for example, a light bulb. 1 footcandle/lumens = 10.76 luxes and 1 lux =.093 footcandles or lumens Where can I purchase a lumen meter? Eco-Schools USA recommends the light meter from Mastech found on Amazon.com. http://www.amazon.com/Mastech-Light-LX1010BS-display- Luxmeter/dp/B004KP8RE2/ref=sr_1_5?s=electronics&ie=UTF8&qid=1342571104&sr=1-5 Mastech Light Meter LX1010BS with LCD display, 100,000 Lux Luxmeter - $20.17 Operating directions Mastech Light Meter LX1010BS with LCD display, 100,000 Lux Luxmeter operating instructions are found on the next page. The unit of measure displays in luxes. This will be a great opportunity for your student to work on conversions.
    [Show full text]
  • Exposure Metering and Zone System Calibration
    Exposure Metering Relating Subject Lighting to Film Exposure By Jeff Conrad A photographic exposure meter measures subject lighting and indicates camera settings that nominally result in the best exposure of the film. The meter calibration establishes the relationship between subject lighting and those camera settings; the photographer’s skill and metering technique determine whether the camera settings ultimately produce a satisfactory image. Historically, the “best” exposure was determined subjectively by examining many photographs of different types of scenes with different lighting levels. Common practice was to use wide-angle averaging reflected-light meters, and it was found that setting the calibration to render the average of scene luminance as a medium tone resulted in the “best” exposure for many situations. Current calibration standards continue that practice, although wide-angle average metering largely has given way to other metering tech- niques. In most cases, an incident-light meter will cause a medium tone to be rendered as a medium tone, and a reflected-light meter will cause whatever is metered to be rendered as a medium tone. What constitutes a “medium tone” depends on many factors, including film processing, image postprocessing, and, when appropriate, the printing process. More often than not, a “medium tone” will not exactly match the original medium tone in the subject. In many cases, an exact match isn’t necessary—unless the original subject is available for direct comparison, the viewer of the image will be none the wiser. It’s often stated that meters are “calibrated to an 18% reflectance,” usually without much thought given to what the statement means.
    [Show full text]
  • Camera Basics, Principles and Techniques –MCD 401 VU
    Camera Basics, Principles and techniques –MCD 401 VU Topic no. 49 Film Exposure Exposure in film photography is defined as the quantity of light that is allowed through the camera lens and onto the photo film controlled by the intensity of light (through the aperture) and length of time (determined by the shutter speed). For correct exposure in a film camera, whether 35mm, medium format, or large format, it is essential that you correctly set both the shutter speed and aperture. Film speed will also play a role in determining the correct exposure. Obtaining the Correct Film Exposure Technically speaking, the correct film exposure does not exist as different photographers will have a different idea of what is properly exposed and what is not. See the example below for three different exposures of the same site. Depending on whether you want to see all the detail or darken it for night will determine the right exposure for you. However, the way in which you get any exposure remains the same. Light Metering Most modern 35mm single-lens reflex (SLR) film cameras have through-the-lens (TTL) meters that intake the amount of light available to help you determine the best exposure. These types of light meters are called Reflective Meters as they measure the light bouncing off your subject and into the camera lens. For beginners using a camera without a light meter, it is highly suggested that you purchase a handheld meter to use. Handheld meters can be Reflective or take 1 Camera Basics, Principles and techniques –MCD 401 VU Incident Light Readings.
    [Show full text]
  • L-308X L-308X-U Operating Manual
    Light Meter L-308X L-308X-U Operating Manual Thank you for purchasing our product. Please read this operating manual so that you will fully understand the features and operation of this product. Then keep the operating manual in a safe place for future use. Please see the Startup Guide for information about the basic operations. ■ Safety Precautions Before using this product, please read this "Safety Precautions" for proper operation. The WARNING symbol indicates the possibility of death or serious WARNING injury if the product is not used properly. The CAUTION symbol indicates the possibility of minor to moderate personal injury or product damage if the product is not CAUTION used properly. The NOTICE symbol indicates cautions or restrictions when using NOTICE the product. Please read all notes to avoid errors in operation. The NOTE symbol indicates the reference information and related NOTE functions. We recommend that you read these notes. The arrow indicates reference pages. WARNING ● Infants or toddlers may accidentally wrap the strap around their neck, so please place it in a location out of their reach. There is a danger of suffocation. ● Keep the Lumidisc and synchro terminal cap out of reach of Infants or toddlers, as swallowing such objects can cause suffocation. ● Do not place batteries in open flames, attempt to short, disassemble or apply heat to them, use unspecified batteries, or recharge them. They may burst and cause fires, serious injury, or damage to the environment. Polyvinyl Chloride (PVC) cable and cord notice ● Handling the cord on this product or cords associated with accessories sold with this product will expose you to lead, a chemical known to the State of California to cause cancer, and birth defects or other reproductive harm.
    [Show full text]
  • Average Scene Reflectance in Photographic Exposure Metering Douglas A
    Average Scene Reflectance in Photographic Exposure Metering Douglas A. Kerr, P.E. Issue 1 January 30, 2005 ABSTRACT The quantity “assumed average scene reflectance” is widely mentioned in connection with the calibration of “reflected light” photographic meters. Understanding of its significance is elusive. In this paper, we examine the actual significance of this quantity and how it plays a role in deciding upon a calibration constant for a reflected-light exposure meter. We also examine the significance of various oft-mentioned values of assumed average scene reflectance, such as 18% and 12-13%, and finally discuss the use of a gray card of known reflectance to perform “incident light” metering using a reflected light meter. SUMMARY The quantity “assumed average scene reflectance” is widely mentioned in connection with the calibration of “reflected light” photographic meters. Often questions are raised as to exactly what that means, and as to what numerical value has likely been used in establishing a calibration for a particular exposure meter or in-camera metering system. Also of interest is the matter of using a “gray card” target to perform incident light metering with a reflected light meter. The question is often raised as to what reflectance is most appropriate for direct use of such a card. We conclude that: • The matter of the significance of the average scene reflectance assumed in the calibration of a reflected light meter is not a simple one. • The value of assumed average reflectance of a “typical” scene upon which the calibration of reflected light meters is predicated is commonly 18%.
    [Show full text]
  • Operating Instructions Q Operating Instructions
    EXPOSURE METER Operating Instructions q Operating instructions SAFETY PRECAUTIONS This manual uses the following safety labels for AWARNING and ACAUTION that you must follow. /b WARNING Indicates hazards or unsafe practices that can result in severe personal injurry or death. ACAUTION Indicates hazards or unsafe practices that can rresult in personal injury or damage to your L-308Bll exposure meter. (CAUTIONI Indicates an operation note or limitation you must use. Please read the notes to avoi d an incorrect L-308BII operation. NOTE(S) Provides the reference information and related functions that are useful for your L-308Bll operations. /bA WARNING &ZAUTlON CONTENTS SAFETY PRECAUTIONS .......................................................................................... i CONTENTS .................................................................................................................... ii 1. Parts Designations ...................................................................................... 2. Display ................................................................................................................... 2 2.1 LCD panel .................................................................................................................................. 2 3. Mode Selection ................................................................................................ 3 3.1 Switching between incident light metering and reflected light metering ........... 3 3.2 How to fit the Lumidisc ........................................................................................................................
    [Show full text]
  • EV - LV - ISO Relationships
    EV - LV - ISO Relationships By Dick Sullivan EV Exposure Value Table f 1.4 f 2.0 f 2.8 f 4.0 f 5.6 f 8.0 f 11 f 16 f 22 f 32 1 s 1 2 3 4 5 6 7 8 9 10 1/2 s 2 3 4 5 6 7 8 9 10 11 1/4 s 3 4 5 6 7 8 9 10 11 12 1/8 s 4 5 6 7 8 9 10 11 12 13 1/15 s 5 6 7 8 9 10 11 12 13 14 1/30 s 6 7 8 9 10 11 12 13 14 15 1/60 s 7 8 9 10 11 12 13 14 15 16 1/125 s 8 9 10 11 12 13 14 15 16 17 1/250 s 9 10 11 12 13 14 15 16 17 18 1/500 s 10 11 12 13 14 15 16 17 18 19 1/1000 s 11 12 13 14 15 16 17 18 19 20 Exposure Values: The Table above shows the range of EV (1-20) that an SRT is capable of being set to, in Whole Stops, f 1.4 to f 32 and 1 second to 1/1000 second. The table does not show Intermediate or Half Stops such as f 1.2, f 1.7, f 3.5, f 4.5, etc. They of course, would be between the Whole Stops, and produce fractional EV numbers. Each EV number represents one stop in exposure.
    [Show full text]
  • PLSB S11 Acc-Light Meters
    Section11 Accessories - Light Meters Introduction . 720-721 Gossen . 722-725 Spectra Cine . 725 Minolta . .726-728 Pentax . 729 SourceBook Polaris . 730 Sekonic . .731-734 Novatron . .735 Lighting SP Studio Systems . .735 Wein . .735 The rofessional Photo, Video, Cine & Theatrical Photo, Video, P for LIGHT METERS INTRODUCTION TO LIGHT METERS the same exposure for each Advantages of Incident object, to render a consistent Measurement Incident Measurement exposure. Light meters are Incident meters measure accu- calibrated to assume that all rately and consistently and are subjects are of average 18% not affected by variances in reflectance, or neutral gray. reflectance of the subject or The use of the 18% neutral scene. Because of this, incident gray standard allows a reflect- meters give the most accurate ed light meter to render cor- exposure for the majority of rect readings for “average” situations and subjects. subjects in “average” lighting situations. (The value of 18% Reflected Metering neutral gray is also referred to Reflected metering reads the as Zone V in the Zone System, intensity of light reflecting off an advanced black and white the subject and may vary exposure method.) according to variances in Reflected tonality, color, contrast, back- Incident Metering ground, surface, or shape. The incident meter is aimed Measurement Meters are designed to regard at the light source and meas- all subjects as 18° neutral gray ures the light source falling reflectance. Reflected measure- directly on a scene and is not ment of any single toned area influenced by the reflectance will result in a neutral gray of the subject being pho- rendition.
    [Show full text]
  • Sverdlovsk 4 Manual
    Photoelectric exposure meter Sverdlovsk-4 instructions (English translation) This manual has been translated and edited from the Russian original Contents 1. Description and features ............................................................................................................................................................ 3 2. Kit contents ................................................................................................................................................................................. 3 3. Technical specifications ............................................................................................................................................................. 4 4. How to use the meter ................................................................................................................................................................. 6 Measuring the exposure ........................................................................................................................................................ 6 Checking the battery level ....................................................................................................................................................10 Replacing the battery ...........................................................................................................................................................10 Methods for measuring exposure .........................................................................................................................................12
    [Show full text]
  • Light Meters for Photo/Video/Cinematography
    w 200mm Photo Meters CINE Meters Illuminometers light meters for photo/video/cinematography w ７０mm L-758 SERIES DIGITALMASTER | L-478 SERIES LITEMASTER PRO | L-308DC DIGICINEMATE L-308S FLASHMATE | L-389A STUDIO DELUXE III | L-208 TWINMATE | i-346 ILLUMINOMETER www.sekonic.com ................................................................................................................ For over 60 years, Sekonic Corporation has designed and manufactured the most innovative and sophisticated light measuring instruments in the photographic and Cine/Video industry. Our commitment to meet and exceed the demands of the professional and their expectations continues with a vigorous passion. From our humble beginnings, it all started on June 16th, 1951, when Mr. Ryuichi Mitani, a young man at the time, established “Seiko Electronic Co. Ltd” an engineering, manufacturing and design company for exposure meters and selenium purification systems. That same year the company released their first exposure meter, the L-1 under the brand name of Sekonic. By 1960 the Sekonic brand meters became so popular that the company changed the name from Seiko Electronic Co. Ltd to Sekonic Corporation, a true testament that Sekonic meters were destined for success. The company grew over the years and in 1963 it was listed on the Tokyo Stock Exchange. Sekonic’s detail to precision engineering and business expertise in the electronics business landed them many notable OEM clients such as Copal and Konica. In 1974 Sekonic received the “Good Design” award from the Ministry of International Trade and Industry in Japan for the L-428 System Meter. Sekonic would later be honored with this prestigious award again in 1994 for the L-308B Flashmate.
    [Show full text]