1. Reminder: Please use our affiliate links for holiday shopping!

"Ubderstanding Exposure" book question.

Discussion in 'Open Discussion' started by Phil66, Mar 17, 2012.

  1. Phil66

    Phil66 Mu-43 Regular

    130
    Dec 27, 2011
    Ello all,
    I am reading (again) the book Understanding Exposure by Bryon Peterson. In the section called "The Sky Brothers" he show a picture of a schoolhouse in a snow filled landscape. He says that when he pointed at the schoolhouse and took the shot the snow turned out grey! Then he goes on to say "This would happen whether you're in manual or automatic exposure mode. Amd why not? The light meter is doing exactly what it should do when shooting a white subject--making it grey......"
    Why is this so? Why should a light meter make white things grey???
    Cheers

    Phil:confused:
     
  2. ~tc~

    ~tc~ Mu-43 Hall of Famer

    Oct 22, 2010
    Houston, TX
    Because it's calibrated that way so that blues, greens, reds, etc come out right. If there is a lot of white in your scene (snow, sand, clouds) you need to dial in some +EV exposure compensation, which seems counter-intuitive because these scenes are usually bright.
     
    • Like Like x 1
  3. ill_dawg

    ill_dawg Mu-43 Veteran

    201
    Aug 26, 2010
    The light meter takes all the light coming into your sensor and tries to make it a neutral grey. If you want it to do something different, you need to meter off of something other than the whole scene.

    Sent from my HTC Vision using Tapatalk
     
  4. Kees

    Kees Mu-43 Regular

    56
    Jun 30, 2011
    The Netherlands
    Kees Dignum
    Anselm Adams once calculated that the average "lightness" of an average scene is 18% grey. This value is used to calibrate cameras. The camera will always (if not in manual mode of course) calculate the settings to get a picture that is 18% grey. It will also do that if the actual scene is a snowy landscape for instance (much lighter than 18% grey) and thus make the snow look grey and the picture much darker than the actual scene.
     
  5. WJW59

    WJW59 Mu-43 Veteran

    235
    Feb 20, 2011
    Light meters are calibrated somewhere around a middle gray (think gray card) so it assumes that whatever it is pointed at reflect about that much light. Since a "normal" scene, with mixed colors and varying amounts of reflectivity, is supposed to be close to the gray card this is not a problem. When you get a scene that has large areas that are brighter (Snow, beaches, etc.) the meter assumes it is normal reflectivity and sets exposure accordingly. Modern cameras with multi-zone evaluative metering systems are less likely to be fooled by bright (or dark) scenes but are still not perfect.

    Back up and re-read the "18% Reflectance" section.
     
  6. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    SoCal
    That is how a light meter works. A light meter will see everything as 18% gray (some meter may differ slightly in their %, some see 12%). In manual, you read off a white sheet, center the needle, perform no manipulation in processing and that white sheet is now an 18% gray sheet. Point the meter at a black sheet, center the needle, no manipulation in processing and that black sheet is now 18% gray.

    A meter is a guide and not a law. To obtain consistant and proper exposure results in different lighting situations, one needs to understand how a meter works and what adjustment are necessary to attain a proper exposure.

    For example green grass is roughly 2/3rd of a stop to one stop darker than 18% gray. So one must compensate for the difference between the actual gray density of the grass and what the meter is telling you. The compensation is to close down (darken the final image by 2/3rd to 1 stop). In other words fill the viewfinder with grass, center the needle, then close the aperture by 2/3rd of a stop or increase the shutter speed by 2/3rd of a stop ... Viola! a proper exposure.

    Another example is to take a reading off the palm of your hand. Your hand is approximately one stop lighter than 18% gray. Same as above, fill the viewfinder with your hand, center the needle, then open up the aperture by one stop or lower the shutter speed by one stop.

    In either case you need to be in manual mode and your hand or the grass needs to accurately reflect the light as it is reflected off your subject. (If your subject is in shadows then the grass or your hand also needs to be in shadows, et cetera.)

    If you use the meter as a your guide and apply an appropriate compensation to what your meter is seeing, then your white sheet will end up white without any processing manipulations and your black sheet will end up black without any post manipulations.

    I have only scratched the surface of metering, but metering accuracy will significantly affect the IQ of your final image.

    Gary
     
    • Like Like x 3
  7. ~tc~

    ~tc~ Mu-43 Hall of Famer

    Oct 22, 2010
    Houston, TX
    Only one point, you don't need to be in manual mode. It is generally simpler to accomplish the same thing with the exposure compensation setting in P, A, or S modes (generally the advice given by Bryan in the book)
     
  8. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    SoCal
    While, yes that is true, it is one step away from easily having full control of your camera. EV Compensation is sorta like an automatic transmission, much easier than a manual transmission, you get where you want to go, but you really don't know how you got there and there is a lack of control when compared to a manual transmission. With a manual transmission you really have to concentrate on the road conditions, the clutch, the gas, the gears ... the whole shebang. For many this control makes them a better driver and for others the driving experience more enjoyable. (Granted, under certain conditions a manual transmission is a pain, just like Manual in a camera.)

    EV Compensation only works well with uniform lighting. Once the lighting changes or your subjects changes lighting positions or you change your position or you change your subject then you need to start the entire process again. So to with Manual, but in Manual you can see your meter change and apply a thought process of "What does that really mean?" to the meter shift. In EV Compensation the camera will change the settings automatically, whether that change is good or bad will only determined by review. In Manual, I think it is easier for you to determine before releasing the shutter if the setting are what you truly desire (previsualization).

    One can also use ISO to compensate for 18% gray, but, like EV Compensation, it is a bit more complicated/nebulous than aperture and shutter speed, so I didn't speak to that methodology as well.

    The beauty of shooting in Manual is you learn how aperture, shutter speed, ISO and your light meter all work together. That understanding will help many become a better photographer.

    Gary
     
    • Like Like x 1
  9. ~tc~

    ~tc~ Mu-43 Hall of Famer

    Oct 22, 2010
    Houston, TX
    The decision of whether to use manual mode or one of the others is totally up to each individual photographer. IMHO, the "teaching" effect of manual mode is arguable, and comes at great risk of totally blown exposures.

    The exception to this, is of course, if you have consistent lighting and can take advantage of the "sunny 16" rule(s), but I rarely have that opportunity, and when I do, it's usually an "easy" exposure situation, like an airshow or something.

    As most of my photography is travel, and very often from a moving car or other similar "hurry up" situations in constantly changing light, I can not afford the risk of the blown exposure. Yes, the meter may get it off slightly, but usually will get it "close enough" in the majority of situations. Exposure compensation can easily convert the "close enough" into "really really good".
     
  10. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    SoCal
    When I was a news photog, my job depended on not blowing the exposure ... one only has to look at a daily newspaper to see how varied the lighting conditions and assignments are for a photojournalist ... I and my peers shot in manual.

    Gary
     
  11. supermaxv

    supermaxv Mu-43 Veteran

    273
    Sep 20, 2011
    I do think taking the time to learn how to control your camera effectively in Manual (a la Peterson) is extremely useful if you have any interest at all with using a flashgun, even if you're using TTL. It's really amazing how easily you can control things like subtle ambient light exposure in a dark room when shooting with an electronic flash and being in complete control of your exposure on the camera.
     
  12. ~tc~

    ~tc~ Mu-43 Hall of Famer

    Oct 22, 2010
    Houston, TX
    Understood, and appreciated, Gary. But admittedly, those were back on the days of unreliable metering, not today's advanced evaluative programs.
     
  13. MajorMagee

    MajorMagee Mu-43 All-Pro

    Feb 24, 2011
    Dayton, OH
    Just a quick example of how the sky brothers, as explained in "Understanding Exposure", works. These were done by spot metering in and around the sun and cloud to get different light meter readings that completely change the look of the cloud.

    [​IMG]
    f6.3 at 1/1000 sec

    [​IMG]
    f8 at 1/1600 sec

    [​IMG]
    f9 at 1/2000 sec

    [​IMG]
    f11 at 1/2000 sec

    E-PL1 with PL 20mm f1.7
     
  14. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    SoCal
    Not at all ... On-board Center-Weight Metering for Nikon, plus I used a handheld Pentax Spotmeter and a Sekonic incident meter. There is a difference between unreliable and accurate.

    The older meters used in the film only days were very reliable, plus film has greater latitude/margin of error than digital.

    Today's digital camera meters are far more accurate than the film camera meters of ol' ... but they have to be. When I first acquired a dSLR (20D), my next purchase was a handheld incident meter. I metered and shot as I had with film. My stuff came out terrible. I soon realized that digital metering required greater care and accuracy than film.

    Recently, I shot basketball and soccer using 'A', because of the uniform lighting, w/ EV compensation applied. I also just shot a stage performance, the lighting was so wild and changing that I shot it in manual.

    Gary

    2CBL2402.

    IMG0373-L.

    [​IMG]
    Mamadou Ndiaye, at 7'-5", is reportedly the tallest basketball players in America (pro, college and high school). Ndiaye is still a junior at Christian Brethren High School in Huntington Beach, CA.

    501183668_y8ftz-XL.