Re: Light Meter - Exposed vs Retracted Dome

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ectobuilder

Veteran
Re: Light Meter - Exposed vs Retracted Dome

Could someone please tell me why I would need to do the following when metering light:

SCENARIO 1: Pointing the lightmeter AT the camera FROM the subject with dome retracted or exposed
SCENARIO 2: Pointing the lightmeter AT the key light FROM the subject with the dome retracted or exposed
SCENARIO 3: Pointing the lightmeter AT the subject FROM the subject with the dome retracted or exposed
SCENARIO 4: Pointing the lightmeter AT the subject FROM the camera's position with the dome retracted or exposed

I'm confused as to WHY I should do any of these EIGHT scenarios (i.e. retracted or exposed dome x Scenario 1, 2, 3, 4)

Thanks!
 
Scenario 1 with the dome exposed is meant to give an overall exposure value. Doing so with the dome retracted is usually not done because if for example, you have a side key, the light won't hit the dome as much.

Scenario 2 with the dome retracted lets you meter individual lights so that you can determine your key to fill ratio. Doing so with the dome exposed is usually not done because you're trying to measure only one unit at a time, this can allow other units to interfere with the reading more easily.

Never heard of scenario 3.

Scenario 4 usually doesn't even involve using the dome, but instead the spot meter. This gives you a more precise reading since it takes into account what the subject (or whatever you point it at) is reflecting back towards the camera, not the light that's hitting it. Also a useful tool for measuring practicals or windows to make sure they don't blow out.
 
Wouldn't SCENARIO 3 be for checking things like green screen to see how uniform the light is falling onto it?

Also, to get an overall exposure value FROM the camera's perspective (meaning what to set in the camera) wouldn't you place the light meter at the camera TOWARDS the subject with the dome exposed?

I guess I am confused between the concepts of light FALLING onto the subject and FALLING onto the camera's sensor and how that affects metering (i.e. where to point the meter to/from and when to expose/retract the dome)
 
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ectobuilder said:
Could someone please tell me why I would need to do the following when metering light:

SCENARIO 1: Pointing the lightmeter AT the camera FROM the subject with dome retracted or exposed
SCENARIO 2: Pointing the lightmeter AT the key light FROM the subject with the dome retracted or exposed
SCENARIO 3: Pointing the lightmeter AT the subject FROM the subject with the dome retracted or exposed
SCENARIO 4: Pointing the lightmeter AT the subject FROM the camera's position with the dome retracted or exposed

I'm confused as to WHY I should do any of these EIGHT scenarios (i.e. retracted or exposed dome x Scenario 1, 2, 3, 4)

Thanks!
Click to expand...

You are mixing up types of meters in these listed methods.

An 'Incident' meter would be used to 'point at the lights' directly. That is measuring the light 'incident' on the subject.

The Dome or NotDome choice is how much of the 'light incident' on the subject you want to measure... for the 'dome' setting, you would be measuring all light coming from approximately the 'half sphere' in the direction of the meter's orientation.

So in that scenario if there are 3 lights, the meter reading will be an 'average' of all the 3 lights.

The NonDome setting will change how much of the half sphere will be measured. This will allow you to find 'contrast ratios' of the incident light, and depending on how separated the 3 lights are, you will read each one nearly 'individually'...

When you point a meter 'at the subject' you must use a reflective meter (or switch to reflective mode...) and are measuring the light that is reflected from the subject, or surfaces. You place the meter in the approximate direction of the camera, since the light reflected in that direction is what will be captured by the film or sensor.

Again placement and orientation of the reflective meter will 'average' more or less of the scene into the 'meter reading'.

Since I have two types of meters I use the following:

I use an incident meter to find the basic amount of light falling on the subject, and these days I'm thinking more in terms of footcandles, and trying to achieve a specific footcandle value of the light, say 100 footcandles. For contrast ratios, I will check the light incident from the several lights available, which may require turning lights on or off depending to get accurate individual readings.

I will use a spot meter for my 'reflective meter' and usually take that from where the camera is placed, so that I know the reflective surfaces that are in the scene, have sufficient light for my camera to register an adequate image.

If I am the director and not the 'camera person' and the 'camera person' doesn't do that sort of 'work'... I supply the meters and 'assist' in determining these things...
 
ectobuilder said:
So when the dome is retracted does it become a spot meter?
Click to expand...

No. A 'spot meter' has an angle of measure of about 1 degree. One looks through the spotmeter which has a lens and set the 'circle', similar to a 35mm metering indicator, on the surface that is to be measured.

The 'dome' vs 'non-dome' for an incident meter changes the 'angle' between approx. 180 degrees, and perhaps 30 degrees. Same for the reflective meter.

There are some meters that have a number of options, and some have 'accessories' that allow it to change from incident, to reflective, to spot. The Sekonic L-758 (DR or Cine) is one such meter.
 
I read somewhere that reflective meters use grey scale to resolve the exposure. Is this true and why is this so?

If true, then in order to make an incident light meter to become reflective, does it have to have a setting that restricts it to seeing grey scale color only?
 
An incident meter is intended to measure the light falling on the scene itself, not subject reflectance values. A spot meter measures reflected scene values and practical light sources within the camera's view.
Scenario 1 is usually with the dome exposed to give an average reading of all lights illuminating the subject within a 180 degree angle. If you read the reflectance value of an 18% reference gray card with a spot meter it should give about the same reading.
Dome retracted restricts acceptance angle to about 90 degrees. Normally this is used to directly read and separate key, fill, ambient shadow and back light values to establish scene lighting contrast ratios. The meter readings still give what would be a correct exposure for 18% gray reference value for each source. Deciding what exposure to shoot with, i.e. where to expose for 18% reflectance value, is ultimately a creative choice.

Some incident meters provide a separate cover that fits over the retracted dome to recalibrate the meter for average scene reflectance within usually a 40 degree averaged cone of acceptance. Some also, like Sekonic's new L478, have a separate accessory attachment that turns it into a spot meter with a viewfinder for aiming.

I love incident meters. I like to know what the light itself is doing. With fore knowledge of key and shadow values and overall contrast ratios, accurately placing exposure for maximum DR capture becomes much easier. The best way to learn how to do this is by learning the basics of Ansel Adams zone system photography. With a little practice it becomes second nature to look at a scene and visually judge where to set exposure for the creative results you want. A couple of links below may help.

http://photo.tutsplus.com/articles/theory/understanding-using-ansel-adams-zone-system/

http://www.russellcottrell.com/photo/BTDZS/index.asp

http://f164.com/the-zone-system-for-digital/10/2011/
 
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ectobuilder said:
I read somewhere that reflective meters use grey scale to resolve the exposure. Is this true and why is this so?

If true, then in order to make an incident light meter to become reflective, does it have to have a setting that restricts it to seeing grey scale color only?
Click to expand...

A reflectance meter is calibrated to give a reading based on the exposure of a '18% grey card'. There are some different formulas and correction factors but that's the essential 'intent'.

An incidence meter is calibrated to give a reading based on incident light striking an '18% grey card'.

The actual sensor has a spectral sensitivity, but in a 'broad' sense it measures light visible to the eye...

A colorometer would measure 'intensity' in the various 'color bands(RGB)', and a color temperature meter, more useful to practical photography would measure the dominant 'color' cast of the incident light.
 
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