 BetterPhoto Member |
Light Meter Readings When using a light meter, I find I get a different reading when taking a reflective reading than when taking a incident reading. Most of the time the incident reading requires 1 stop more exposure. Is this normal for comparing these two readings?
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
Different readings, yep. How many f/stops difference depends on the color/reflectivity.
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Bob Cammarata |
If your hand-held meter reading requires a stop more exposure than the reflected light meter recommends (in the same light), it's because the (reflected) metered object is a stop brighter than neutral gray. As Greg pointed out, the metered object reflects more light back into your lens and onto the film (or sensor), and can give you a false reading. (This is similar to metering white snow, which can be TWO stops off.) In this scenario, your incident reading will be the most accurate. You will find that a gray card placed at the same location, and in the same light, will yield similar exposure recommendations.
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David King |
The issue actually goes deeper than most texts indicate. The age old adage that all exposure meters are based on the 18% gray card is true ONLY for incident meters. ANSI standards for reflective meters allows a range of from 10% to 14% with the average being around 12%. This yields about a 1/3 to 1/2 stop difference in readings from an incident reading and a reflective reading from a gray card all other things being equal. The solution is to calibrate your reflective meter and/or to calibrate you system including meter and camera to yield an exposure based on where the actual exposure threshold is for your film. To do it precisely requires a densitometer and some mind numbingly boring exercises but is the only way to be truly accurate. Digital, by the way, did not escape this issue and digital cameras need to be calibrated just as film cameras do for accurate exposures. Once the camera/meter/system is calibrated then the issue remains mentioned above about what you have a reflective meter pointed at or how you are handling the incident meter. If real exposure precision is your goal then the best way is to follow the approach of film and video DPs and use a spot meter to set the lighting ratios (or to check them for compatibility with your medium) and then use an incident meter to determine an exposure. For B&W shooters, zone System reading where a spot reading from a shadow or dark tone you wish to place in a given zone is taken and the exposure adjusted accordingly. For digital or transparency film you are better basing the exposure adjustments on a reading of a highlight tone. All of this pre-supposes you really want precise and accurate exposures in order to give you the maximum image data for your final prints. If that is not critical, then there are any number of "rules of thumb" for basing exposures on the readings of various objects and then making adjustments. Those are guesses. They may be consistently close, but 'close' only counts in napalm, horseshoes, and non-critical shooting. From the fact that you have two meters I'd assume you want your readings to be consistently perfect, not consistently close. among my beginning students, right after soft images from hand-held camera movement, the biggest quality issue is imprecise exposures yielding negatives or files that simply cannot be made to yield a perfect print. David
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Norbert Maile |
I am not sure what type of meter you are using. The one that I use is very old, but it has a filter which you atatch to the front for incident readings. I have tested this many times, and it gives an exact same reading as a reflective gray card reading. Norbert
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Larry T. Miller |
I agree with Norbert. My meter does the same thing. I'm using a Calculite XP.
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