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Light Meter Technique

light meter measuring light lambert cosine sekonic

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#1 Ruben Arce

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Posted 29 October 2016 - 03:22 PM

Hello everyone,

 

I've been using my light meter for years (Sekonic 558c) and I've been researching as well for a long time and it's been really difficult to find information on how to properly use a light meter. I have tried books, tutorials, skein videos, workshops and even film school but nobody can tell me how they do it.

 

I know light meter gives you certain information and you decide what to do with that. I know light meters and cameras can very a lot and I know how to compensate or calibrate the meter for a certain camera or gamma. I understand 18% gray, and the zone system, incident and reflected meters. But I know that aiming the meter towards the lens is not going to give me the precision that I'm looking for.

 

Here is my example:

 

I'm using a incident meter, I have a person sitting in front of the camera, facing the lens. I have a light source 90 degrees on the right side, easy right? If I aim the meter towards the lens it is going to compensate for the lack of light on the left side, average both sides and it will give me totally not accurate reading. If I point the light meter towards the light source (I guess is the best way to do it) It will give me a reading that is not taking into consideration the shadow on the left side, and it will be "properly exposed".

 

I have done this for some time and I feel like even when my light meter is properly calibrated for the camera it feels a little underexposed. Is Lambert's Cosine rule affecting that light? Because if the light were aligned with the camera angle then I would have a "on the spot" reading. But in reality (the example) I have the light 90· on the side and I'm measuring towards the light. Is the light reflected from the subject affected by Lambert's Cosine rule? Do I have to compensate? I learned from photography class that when they use "Sunny 16" If the sun (light source) is behind you, you don't compensate. If the sun is on your side then you compensate bu half a stop and if the sun is against you the you open up one stop. I have been using this same compensation values with my readings and it had helped me get even better exposures. Why is this important? Well I want to be able to trust my LM and my judgment when lighting a scene, I want to be able to determine "proper exposure" and get consistent results every time so I can take it from there for more artistic interpretations.

 

What do you think? Can you share your experience or even better your technique?

 

Thanks in advance


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#2 David Mullen ASC

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Posted 29 October 2016 - 07:32 PM

Assuming your meter is accurate, then imagine pointing it at the light from the subject and getting an incident reading.  

 

Now imagine the camera doing a 360 degree dolly move circling around the subject's face.  As you move into a side-lit position, you might feel that the face looks a little darker than the front-lit position, which is what people sometimes like the results of having the incident dome half-lit when metering a half-lit face, because the meter will average the key and fill side.  Personally I'd rather read the key separately by pointing the dome at it, but then this requires you to then decide how much to open up for the exposure to feel "full".  It depends on the mood and the setting -- inside a living room at night, you may not want the face to get to key brightness unless it is very near a lampshade, but inside the room in the daytime, you may want a brighter face.

 

So for a half-lit face, I might open up a 1/2-stop to create something closer to a "normal" brightness.

 

It would be a simple test -- light a face from the side, meter it, and take stills from the front, side, and backlit angle at the same exposure, and then try one where you open-up, let's say, a 1/2-stop for the side and a full-stop for the back position.

 

Experience and testing tells you how much to stray from your meter reading.


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#3 Ruben Arce

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Posted 30 October 2016 - 04:12 AM

David,

 

Thank you so much for your response. I wanted you to answer my question and you did, I appreciate that. You helped me realize something that I didn't wanted to accept, and that's nothing replaces experience and testing. I wanted to hear about a formula, but I guess that's the why cinematography is called a craft.

 

I like your example, that's exactly what I had in mind and I agree that it comes to interpretation and serving the story more than getting "proper exposure"

 

Using a hand held meter had helped me to take advantage of dynamic range on different cameras and that's the way I like working, so any advice on light meter techniques or tips are welcome from David or other users.

 

Thanks


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