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Light Meters, whats the major difference between a reflective meter and an incident meter?


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#1 Jaden Scholes

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Posted 24 June 2014 - 04:15 PM

Hey, Just wondering if someone could clear up the difference between the two kinds of light meters and what kind of film maker would use one or the other. Also if anyone know some cool light to shadow ratios they would like to share that would be much appreciated.

 

Cheers

J


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#2 Michael LaVoie

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Posted 24 June 2014 - 06:01 PM

I've only ever used a light meter with both options.   Generally most light meters will have options for both incident readings and reflective.  Spot meters etc.   A Sekonic L758 will do it all.  A little pricey but you usually only buy this sorta thing once and hope you never lose it.

 

I rarely take reflective readings on people since that's often easy to see with your eye and usually measure more with the incident dome and see what units are sending how much light etc.  But whatever works for you.  These days there's usually a waveform around on some monitor and I often cross check readings with that as well.


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#3 Michael LaVoie

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Posted 24 June 2014 - 06:14 PM

To answer your question more specifically, an advantage of a spot meter over an incident meter is to measure reflected light from a distance on subjects that are too far away for you to meter.  An actor across a street or in a car, etc.  

 

Typically though if an actor is within a reasonable distance, or in an interior I measure the light in the area they are going to be with an incident meter.  Both beginning and end marks so I know how much light is falling and where the light and shadow areas are.

 

Hope that helps.  Someone else will be more precise and scientific about it I'm sure. 


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#4 John E Clark

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Posted 25 June 2014 - 01:30 PM

An 'incident' meter measures the amount of light falling on the scene. A reflectance meter measures the amount of light being 'reflected' from a surface in the scene.

 

Meters are 'calibrated' to give an exposure indication which yield a certain 'density' in Film film. While the method of determining the ISO for a digital camera is different, the general goal is to have the esposure result in known levels.

 

One can determine one's own 'exposure index', by using a grey card, a calibrated step wedge or similar to find an 'personal' ISO value.

 

For reflectance meters:

 

In practice, one has to take in to account the approximate reflectiveness of objects in the scene. Black 'paper', 'dark' wood, etc, may be 5-10% reflective, or less depending... caucasian skin tone may be 30% reflective... a blank white sheet of paper 80-90%, etc.

 

So if one assumes that a meter is calibrated to an 18% grey card... then if one takes reflective readings of those items listed above, one would be off by one or two stops.

 

Hence one needs to 'adjust', usually mentally, for such surfaces.

 

Incident meters:

Since the incident meter reads only how much light is falling on the surface, the exposure the meter indicates, has to be interpreted in the sense of 'if there were an 18% grey card in the scene". However, one does not have to adjust based on the reflectivities of the objects...

 

Spotmeter:

A 'spot meter' is a form of reflectance meter which has a narrow area of sensing the light, and usually allows the photographer to obtain readings at a distance, and over a 'small' area, as most non-spot reflectance meters read a 30 degree angle, which can include other objects, which have different reflectivities. For example a black cardboard square sitting beside a white cardboard square. The wide angle of the ordinary reflectance meter would yield an average of 'black reflectance + white reflectants'... whereas a spot meter would yield two exposure readings for  each of the squares.

 

Sure you can move close to the subject, but if one is too close, then one's own shadow may figure into the reading and skew the results... or if one is taking reading on a person's face... one can not realistically get 'close enough', or at an angle that matches the camera's view... and so a spot-meter would allow one to take such a reading off a small area.


Edited by jeclark2006, 25 June 2014 - 01:30 PM.

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