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Understanding How To Expose Properly: Part Iii.

Discussion in 'General Technical Discussion' started by camerapapi, Sep 23, 2008.

  1. In part 1, I discussed exposure meters and in part II how shutter speeds and apertures combined to form the exposure. If you are using your exposure meter in Auto or Program and you are happy, no reason to read this. You will get very good exposures 90% of the time; that good modern exposure meters are. If the camera is set to Auto or Program, you the photographer will loose control over aperture, shutter speeds and exposure. If you use Vari-program you gain back, to a certain extent, control over aperture or shutter speeds but still you will have no control on your exposures. I want to repeat again that matrix gets as confused under extreme lighting conditions as the other modes. As long as you have to meter from medium tonalities you will have no problems following your meter because as I said previously, all exposure meters, regardless of how much you paid for them, are not perfect and they were all designed to average all the light they "see" to a medium tonality or 18% gray.
    Today it is very uncommon for an exposure meter to come out of calibration from the factory. I still keep the habit of calibrating the meter prior to a major assignment and if I am going to use more than one camera, I make sure both cameras give me the same readings.
    If you have a gray card you can place it in the sun, in my part of the country at 8 AM (EST) is just fine. Then set the camera in manual mode to ISO 200 or 100 if you have that setting. Set the lens to infinity and the aperture to f16. Make sure the card is not shining or you will get an erroneous reading. Meter the card and only the card and do not throw a shadow on it and if the analog indicator points to the dead center you are done. If it does not, move your apertures till it does. Now, when you shoot at the ISO you set before the test, under sunny conditions, for medium tonality subjects, using those settings, you will be guaranteed a good exposure. If you need to close the lens more or to open it more, just use equivalent exposures as I indicated in part II and you are also done. Just remember that your meter should be set to center weighted or spot, never matrix. Matrix metering compensates the exposure on its own and each shot is different since it has to compare the exposure with that of 30k files in memory. How much matrix compensates? I do not really know.
    Now that the meter is calibrated I know exactly what I have to do to take a picture of a medium tonality but if my subject is not medium tonality what should I do?
    Let's assume the subject is bright, like when we are photographing in bright white sand or the snow or even a bright wall. We already know the meter will make the subject medium tone or gray due to underexposure. Bright, reflective subjects require to open 2 stops from meter reading to bring back the brightness. I usually take two exposures, one opening one stop and another opening two. If my subject is dark or black the meter will make the opposite, will also expose for a medium tone making the subject gray or overexposed. If we close the lens one or two stops from the meter reading our subject will be dark or black again. Simple, isn't it? You are in command, not your meter.
    For digital we should always meter from an IMPORTANT HIGHLIGHT. It is not that difficult to recover details from a shadow area, usually at the expense of some increase in noise but when it comes to lost highlights the news are not very good to recover details in those areas.
    In the past, photographers used to carry a gray card with them to meter from it for accurate exposures. You have a "gray card" in the palm of your hand but its reflectivity is usually 36% so open one stop to bring it back to 18%.
    You open your hand to take the reading and you open the lens to compensate. Easy?
    In general, when we take a meter reading from an area of the subject and take the exposure, all other areas of the subject will be properly exposed considering the light illuminating them. I said in part 1 that a spot meter is very accurate in skillful hands because it can take a reading from a very small part of the subject, and this is critical in many situations where there are extremes of light. I like to use spot metering for sunrises or sunsets. I meter from a bright area above the sun and open 1 stop from the reading to bring back the brightness or meter from a medium tonality off the sky and follow the meter. If I meter the fog, like I do here in South Florida in winter, I open 1 stop to get a correct exposure.
    Another useful technique is called "sunny 16." Anywhere in the world, on a sunny day we can get a good exposure setting the camera to f16-1/ISO. Do not expect that bright light to change much till early evening or early morning when metering is necessary. I have done thousands of exposures this way. Even if I use a polarizer I go "sunny 16" (or equivalent exposure) and open two stops to compensate for my polarizer.
    Some specific subjects will not be easy to read and even if a meter reading is obtained it could be way off. An example is night photography. I usually set my camera to ISO 200 and f8. My original exposure is 4 seconds but if not satisfied with that exposure I bracket one stop above or below as needed. WB could be a problem so proceed accordingly. Most subjects do well with WB at night when set to daylight or tungsten.
    A meter reading with an incident light exposure meter is very accurate because they do not meter reflected light but the light falling on the subject. I used it primarily when I have doubts about what to meter or when doing portraits. Be ready to compensate with very bright or very dark subjects but this time you open for dark and close the lens for bright subjects. Remember that a reading from the incident meter is accurate for a medium tonality or when there are no extremes of bright or dark subjects. They need to be placed in the same light illuminating the subject for a correct reading.
    Today, if you have any questions you can always check the histogram, a very useful tool but do not make from chimpping a habit.
    Before closing I want to repeat once again that modern meters are excellent and they will give you a large proportion of properly exposed files. Just remember that they are not perfect and you will have to take over when confronted with difficult lighting conditions or you will never record in your digital sensor or film your subject like you envisioned it.
    I hope this helps to understand exposure a little better.
    William Rodriguez
    Miami, Florida.
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