 Bernard |
Metering Off the Sky: Why? Why meter off the sky, then re-compose on a ground-based subject? Thank you.
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Bob Cammarata |
Metering off a deep blue sky (with the sun at your back) will have an exposure value similar to that off a gray card. In-camera meters measure reflected light so even if the foreground subjects are in "perfect light", the exposure values may be different (... like if a black dog and a gray cat were frolicking in a patch of white flowers). Metering the sky in this case will expose the scene correctly ... as long as you keep the sun behind you. Bob
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Alan N. Marcus |
Hi Bernard, For most of the history of photography, exposure determination was trial and error. In the 1930’s, the electric light meter was just being marketed. At about the same time, Kodak research labs in Rochester (Messrs. Jones and Condit) concluded that the majority of scenes integrated to middle gray. Stated another way; if you examined a typical scene by optically scrambling the light, the tones and shades commingle to battleship gray. This was found to be about equal to a surface that reflected 18% of the ambient light. Kodak products were marketed in yellow boxes. One Kodak recommendation, as an aid to exposure determination, was to measure a Kodak yellow box placed in the scene with an electric meter. Setting a camera as indicated by the meter most often resulted in a near perfect exposure. This was OK for black & white work. The yellow box technique evolved to a gray card or placard advocated in 1941 by the famous nature photographer Ansel Adams and his cohort Fred Archer. Soon serious photographers were carrying gray cards and new fangled electronic light meters. Carrying a gray card can be a pain. Photographers are always looking for gray card substitutes to be found in nature. One can use blue sky or tree bark or parking meters and the like. Most agree, an actual gray card is best.
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Bernard |
Alan and Bob' I understand perfectly what you are saying, your answers have created another question, please bare with me. With the advancements achived in the chip and circuitry of the internal light meter of the D80, is it necessary to purchase an external light meter and gray card? again please bare with me. thank you.
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Bob Cammarata |
I've never felt the need for an external light meter for outdoor work except when I'm using flash (...with which I'm not real comfortable). I do carry a small gray card in my pack for tricky lighting situations with slide films since the margin for error is so narrow. More often than not though, you'll be OK seeking out mid-tones in the same light and metering there. Green grass, fall foliage and bright red objects are a few more to add to Alan's list that meter accurately. Bob
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Alan N. Marcus |
Hi again Barnard, First I am a firm believer that every serious photographer should have a quality light meter in the gadget bag. To me, the exposure meter is about the equivalent of a compass on a deep water sailing ship. The ideal meter would read both reflected light and incident light. The ideal meter would allow spot reading. The ideal meter would also serve to read light emanating from electronic flash. This gadget bag should also contain a gray card. That being said: I would suggest that currently the vast majority of outdoor shots are exposed via the logic of the in-camera meter and its associated chip logic. I feel strongly that this method is likely all that is needed especially true when one can promptly see results on the digital camera’s LCD screen. The light meter evolved around film technology. It stated as a light thermometer that loosely tied temperature to exposure. Next, actual film or paper was exposed to sunlight. The materials naturally blackened with exposure, no chemicals needed. Timing the blackening action allowed calculating exposure settings. Tables describing lighting conditions vs. camera setting deserve mention. The first meters were solar sells, no batteries needed. Next solid state and chip logic, we know no limits. Much of my career revolved around design of light meters used in color printing and more sophisticated instruments known as densitometers used to measure the blackening of films and papers, employed as quality control tools used to control film making and developing and printing. Now retired age 70. Alan Marcus (dispensed questionable techno babble)
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Bernard |
Alan, Bob thanks, my next purchase will be a Nikon flash, a light meter, and gray card, my Dad knows nothing about photography, and the only way I got him to agree to dish out the funds for this equipment is for him to read these answers.
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Rom A.G. |
I am a bit confused by the replies. I guess the point of metering off the blue sky is to make sure it stayes blue in the photo, not grey or washed out. Thus, you have to set EV+1 as shutter speed will be 1/1000th on a bright day, point camera at sky, then re-compose on subject. I tried this trick on Bow bridge in central park. With the sun behind me, the bridge is too bright;however, metering off it makes the boats too dark. Problem solves using EV+1.
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Bernard |
Rom , I'll add to that logic, be advised my addition is probably questionable tecno babble. seeing that the camara tries to render everything a neutral gray, if metered off the blue sky, woundn't the camara try to render the blue sky as neutral gray.
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Alan N. Marcus |
Hi Rom, Exposure in this instance is the allotment of light energy delivered to the film or digital chip. Gross over or under exposure results in a spoiled picture. Somewhere in-between is a span that will yield an acceptable picture. This span dictates how tones will reproduce. As an example human skin can be reproduced too dark or to light. A skilled photographer can measure scene brightness with a light meter and adjust the camera setting to obtain a suitable skin tone. Such adjustments and setting are not limited solely to a skin tone. A skilled photographer can apply exposure control and exercise control over the rendering of memory colors (tones) such as snow, or sand, or water, or sky, or the like. Logic would tell you that the center tone we call middle gray should be replicated by a surface with a 50% reflection. However, the human eye brain tends see in tone steps that are not equal. As a result an object with an 18% reflectance appears to us as middle gray. See the works of Albert H. Munsell. As to exposure theory: If a scene in nature is exposed so that an 18% is rendered correctly, all other tones will be rendered correctly by law (law of reciprocity (Hurter & Driffield). This is true if the tones do not exceed the range of the film or chip (dynamic range). Now the Colored objects like oranges or sky or lemons, are identified first by hue (red, yellow, green, purple-blue and red-purple). Then by value or scale of reflectance i.e. dark, medium, light etc. Now in this instance we are trying to render the sky correct as well as most all other tones. We know that if we had a gray card and a correctly calibrated meter we could measure the gray card, set our camera as indicated and voila a correct exposure results. In lieu of a gray card we hunt for a substitute. We can choose blue sky, not because it is blue but because its value (intensity) is about at the middle of the scale thus it can serve as a suitable substitute. Alan Marcus (often dispenses questionable techno-babble)
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Bob Cammarata |
A deep blue sky WILL stay blue and whites will stay white...not blown out. "...seeing that the camera tries to render everything a neutral gray, if metered off the blue sky, woundn't the camera try to render the blue sky as neutral gray?" Yes,...and it will with black and white film. Bob
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