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DPChallenge Forums >> Photography Discussion >> What do light meters tell you?
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 02/18/2006 04:49:28 PM · #1
Do they tell what settings to use or do they tell you how lit up the area is around the subject or somthing? Like how much candle power or somthing?
 02/18/2006 04:53:38 PM · #2
there are two types, reflective and incident, yes measure how much light is falling on the subject or how bright the area is.
 02/18/2006 05:03:20 PM · #3
some tell you settings
some tell you raw data
some tell you spot readings
some tell you the general level ..

depends on the meter ...
 02/18/2006 05:06:02 PM · #4
Originally posted by BowerR64:
Do they tell what settings to use or do they tell you how lit up the area is around the subject or somthing? Like how much candle power or somthing?


Yes- they tell you which settings to use for proper exposure. However, proper exposure of the scene is not always guaranteed with a light meter.

You know when you push your shutter button halfway down on your 350d and it gives you what shutterspeed and aperture it will take the photo at? That is your camera's light meter working.

I use mine for my studio strobes because it is the easiest way to get proper exposure for such a short burst of light.
 02/18/2006 05:19:51 PM · #5
Hi,

I'll add a bit more information here. A reflective light meter is used by pointing it at the scene you want to photograph. It measures the light being reflected by the scene. The number you get is not candle power, but it doesn't really matter what it is. On older meters, you set the ISO rating of the film on a dial and then turn the dial to the meter reading you got. Then the dial shows all the f/stop and shutter speed combinations you can use for a correct exposure. New electronic meters skip the mechanical dials and show you the exposures directly.

An incident meter is similar but it measures the light shining on the subject rather than the reflected light. You go into the scene and point the light meter at the light source to take the reading.

There are also spot meters that have a small telescope in them. These measure the light from a small area rather than from the whole scene.

Finally, there are light meters designed to measure the light from strobes.

There is not much point in bothering with a light meter when you are using a digital camera.

--Dan
 02/18/2006 05:20:04 PM · #6
Do they use spot point for the lighting? If they tell the lighting how do they display it? in candel power or do you set that? I dont have a 350D

Do light meters measure like the V1? Hologram
 02/18/2006 07:06:00 PM · #7
Light meters in cameras are calibrated to "zone V" (zone 5). They measure the light being reflected off the portion of thr scene that is being metered and assume that this portion of the scene should be rendered as a Zone V, and give you the "correct" exposure to do that. Zone V is the middlemost gray of the following strip:



If you fill your frame up with a white card and give the indicated exposure, then replace the white card with a black card and give the indicated exposure, the two frames will, in theory, reproduce as identical, Zone V gray frames. In other words, an in-camera meter will underexpose a white card and overexpose a black card.

Hand-held light meters may be "reflectrive light meters" (like the one in the camera), measuring the light that is reflected from the subject, or incident light meters, which measure the light falling on the scene. The incident light meter will, in theory, correctly reproduce all tonalities in the scene because it measures the actual light falling on the scene, whereas the reflective light meter measures the light being reflected back at the meter and has no way of knowing if it's a little bit of light reflecting off a bright surface or a lot of light reflected off a dark surface.

Using in-camera light meters, it is important to understand the concept of "exposure compensation"; if the scene you are metering is predominately light in tone you will need to use exposure compensation to add exposure to correctly render the scene. If the scene is predominately composed of dark objects, you will need to subtract exposure to render the scene correctly. This is the purpose of the exposure compensation dial on your camera.

It is also to important to know which exposure mode your camera is set in, and which areas of the scene it is metering. Cameras may have a "spot meter" mode, where the metering is done on a limited, central portion of the image, or an "average mode", which reads the entire scene and averages its value, or a "center weighted mode", which reads the whole scene but weights its average heavily towards the central portion of the scene.

You need to read your camera manual, learn when to use which of your possible modes, and when to make adjustments to the base exposure to compensate for lighter- or darker-than-normal scenes.

Robt.

Message edited by author 2006-04-07 11:31:17.
 02/18/2006 10:11:37 PM · #8
If its a point meter can i point it to a dark spot on the picture then hold it and then take a shot with it framed properly?

Manuals are very vague when it comes to stuff like this. It tells me spot, center and evaluate.
 02/18/2006 11:13:40 PM · #9
Originally posted by BowerR64:
If its a point meter can i point it to a dark spot on the picture then hold it and then take a shot with it framed properly?


Yes. Let me give a concrete example. You are shooting a picture of a young girl holding an umbrella in a garden. You want her to be on the right side of the image, not in the center. In a normal shot, she would be under exposed because there is not as much light under the umbrella. Solution: set your camera to spot mode, point it at the girl's face, and then press the shutter half way. The camera will focus on the girl and set the exposure so that her face is correctly exposed. Then move the camera to compose the picture the way you want it to be and press the shutter button the rest of the way to take the picture.

The danger in this is that the garden will be over exposed and the highlights will be blown out. I think that the best strategy in difficult lighting situations is to bracket your exposures. Take three pictures, one at what your camera says is the correct exposure for the girl and two more with exposures one f stop above and below this exposure. Many digital cameras can be set to do automatic bracketing.

--Dan
 04/07/2006 07:45:58 AM · #10
WIch would be better for taking pictures of shinny subjects? like cars or guitars? spot metering?

You know there will be reflections so would i want to point the spot on the shiny part then move it to compose the shot?
 04/07/2006 11:35:20 AM · #11
Originally posted by BowerR64:
WIch would be better for taking pictures of shinny subjects? like cars or guitars? spot metering?

You know there will be reflections so would i want to point the spot on the shiny part then move it to compose the shot?


If you read what I posted earlier, you know that your meter is giving you the exposure that will render the tone metered as a zone 5 gray. If you meter the bright reflections and use the indicated exposure, the image will be underexposed. In almost any case, if you meter specular reflections (hot spots) the image will be seriously underexposed. See the landscape learning thread and scroll down a bit to see another discussion of this and some examples of how a meter works.

Basically if you are spot-metering the bright areas of a scene you want to set exposure compensation at plus 2 to get the correct exposure.

Robt.
 04/07/2006 11:49:55 AM · #12
Originally posted by wheeledd:

There is not much point in bothering with a light meter when you are using a digital camera.


The on-board reflective light meter will do the job in many cases, particularly if you think about the reflectivity of the subject your metering and adjust accordingly, but there are many situations when a stand alone light meter, particularly an incident light meter will do a much better job. The onboard light meter (a) isn't an incident meter and knows nothing about the type of object you're metering and (b) isn't perfect. Think about what a stand alone light meter looks like. It's got that little white dome that helps it measure all the light coming from a 180 degree field of view, whereas your cameras light meter is stuck somewhere within the camera's architecture...who knows how much of the light it's actually measuring and how well it compensates for what it's missing.
 04/07/2006 11:59:00 AM · #13
Originally posted by Bear_Music:
Basically if you are spot-metering the bright areas of a scene you want to set exposure compensation at plus 2 to get the correct exposure.


A more formal alternative to this (where the exposure compensation mentioned above is an "educated guess") is to use your light meter to take two readings: 1) take a reading on the highlights, and 2) take a reading on the shadows and then 3) determine and exposure that is between the two of them. Some light meters even automate this task for you and let you average multiple readings to come up with the best exposure.

04/07/2006 12:08:57 PM · #14
Originally posted by dwterry:
Originally posted by Bear_Music:
Basically if you are spot-metering the bright areas of a scene you want to set exposure compensation at plus 2 to get the correct exposure.


A more formal alternative to this (where the exposure compensation mentioned above is an "educated guess") is to use your light meter to take two readings: 1) take a reading on the highlights, and 2) take a reading on the shadows and then 3) determine and exposure that is between the two of them. Some light meters even automate this task for you and let you average multiple readings to come up with the best exposure.


Actually, if you have a camera that DOES do spot metering, it's not an educated "guess", it's precisely what you need. If the camera does "center weighted" metering, it becomes a matter of educated guesswork.

The problem with "letting the camera average multiple readings" is that this will often NOT provide you with the "correct" exposure, because in digital the correct exposure is always highlight-based. If the range between shadow and bright is extreme, an averaged exposure will blow the bright areas (you see it all the time in sunset shots) and there's no way to recover detail from blown highlights.

Robt.
 04/07/2006 12:12:16 PM · #15
I always post a link to this site when these sorts of questions come up - I gained a lot of understanding reading it - I learned how to live without a light meter if I need to and to use the one on my camera much better.

The Ultimate Exposure Computer

Message edited by author 2006-04-07 12:12:32.
 04/07/2006 12:46:20 PM · #16
The only reason I called it an "educated guess" is that, if you only take one reading (off the highlights) then how do you "know" that that one reading is "two stops under" what the proper exposure would be? Experience would be a good answer. But it could also be wrong. What if the highlights are less important than the shadow detail and two stops leaves the highlights intact at the expense of drowning the shadow detail in darkness?

That's all I'm saying. I wasn't being rude by calling your experience "educated", I was only saying that it may be incomplete and that a pair of meter readings would give you "two points to consider" instead of just one.
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