Light meters...once and for all

[Matt. K]

Let’s sort out some misconceptions about light meters….the in-camera type and the separate hand-held type. I’m gonna stick my neck out here and I know I’ll cop some flack from some of our more experienced photographers…..but here it is anyway. The hand-held (incident type) light meters are NOT more accurate than the light meter in your modern digital SLR. They simply require less thought. Here’s how they differ…the light meter in your camera measures reflected light and will give you a deadly accurate exposure providing it is pointed at something that represents an average daylight scene. So what is an average daylight scene? It is a scene that contains a mixture of blacks, whites and greys that if mixed together in a bucket will give you essentially the same tone as a Kodak 18% grey card. How often does that happen you might ask? Surprisingly, most of the time. The meter in your camera will always presume the camera is metering off a scene that reflects 18% of the light. The problems arise when your scene contains an excess of black or white, then the meter will indicate an inaccurate exposure. Picture a camera on a tripod set to Auto mode. A light shines from behind the camera and the subject is an 18% grey card. The cameras meter will give an accurate exposure value. Let’s pluck a value and say F8 at 1/60. Now replace the card with a black card and what does the camera assume? It assumes the same card is there but someone turned the light levels down. For a black card the meter will now give a reading of around F4 to compensate for what it thinks is a lower light level. Place a white card into the scene and the camera still thinks it looking at the grey card but now assumes that the light levels have been increased….so it now indicates around f16. Note…the correct exposure for the black and white card is the same as for the grey card…f8. Now, what does all this mean for the photographer?...simple, if your scene contains average tones then trust your meter, If your scene contains predominantly dark tones then CLOSE DOWN the iris 1 or 2 stops…if predominantly white tones then OPEN UP the iris 1 or 2 stops. (Note that these are not the instinctive actions one would presume to be correct). After a short while of evaluating tones in relation to the grey card you will become surprisingly skilled and your exposures will be exactly the same as if you used a hand-held meter.

Now, let’s look at the hand held meter. Go back to our camera on the tripod measuring the value of a grey card.. Instead of pointing the meter at the card, we point it at the light source. It will measure F8…same as the cameras meter. But, when we change the grey card for a black or white card the setting still reads F8 because we haven’t altered the brightness of the light. The incident light meter reads the light before it bounces off the subject so it’s not influenced by the tones or the reflectivity of the subject. However, it is still not a perfect light meter and has to be used with some discretion. Both types of meter can’t automatically adjust for back lighting and the photographer has to make an adjustment for that. Also, the incident type meter can be fooled by strong side lighting…so once again the photographer has to use his experience. Another handicap of the incident meter is that you need to use an extra hand to employ it and you need to make sure that the ISO is set to the ISO set on the camera. At around $700 for a decent meter it is also a big investment so is it worth it? Well, for a wedding photographer or someone who shoots a lot of products….probably yes. For a street or sports photographer….no. Regardless of what type of meter you use it still has to be used with intelligence and experience and some evaluation of the scene needs to be taken into account. Basically, if you understand your built-in meter then you have everything you need. Your built-in meter also has one advantage over most incident meters….it reads over a matrix….can sense colours, and has a huge at hand database to assist in fine tuning the exposure. Hope this helps clear things up a little.

[adam]

Thanks for explaining all that, informative and agrees with my thoughts.

However, I usually point the lumisphere of the incident meter towards the camera lens rather than at the lights. Is this a wrong technique? Thanks

[Matt. K]

adam
No. Your technique is correct. In fact I should have made that point in my post. Thanks for the wake up call. It doesn't usually make a great deal of difference unless the light is coming from an extreme direction.

[gstark]

However, I usually point the lumisphere of the incident meter towards the camera lens rather than at the lights. Is this a wrong technique? Thanks

That's the correct technique.

Consider the situation were you to use two- or three- light sources? Which of those would be the correct one to point the meter at?

Do, however, consider that, where multiple light sources exist, just as Matt has stated with backlighting, you may need to take extra readings and use your judgment/intelligence to determine where the best value lies.

I would often take three or four incident readings from various parts of my subject, to ascertain how evenly the light was falling over that subject.

[big pix]

I find that spot metering helps with tricky lighting..... meter off the area you want to have the correct exposure...... if using a zoom lens and you have time, zoom in do some spot metering, set camera and shoot....... or use your exposure compensation to adjust for the under or over exposure....... but if using a hand held meter see matt K post above

[adam]

Basically, if you understand your built-in meter then you have everything you need.

Actually I bought the lightmeter as a flashmeter to use with flash, because I don't think my camera's reflective metering works with the flash (have to trigger the flash when I meter)

[Matt. K]

adam
The flash meter function of most hand held meters is far more useful (to me) than the light metering capability. It is a good reason to buy one.

[Reschsmooth]

Thanks for summarising into one piece an assortment of bits and pieces I have read over time.

Makes great sense.

To put into a practical perspective, and from too much timing on ebay looking at black camera gear, photos of cameras and lenses that are automatically metered off the black surface will show the camera as a dull grey. Properly adjusted (slightly underexposed), the camera/lens will look black.

The same with a white subject - relying on the metering without adjustment will show the white subject as a grey.

Is that correct?

[ATJ]

Actually I bought the lightmeter as a flashmeter to use with flash, because I don't think my camera's reflective metering works with the flash (have to trigger the flash when I meter)

iTTL basically does that for you. It sends out a couple of preflashes, evaluates the result and sets the duration of the main flash based on what it "sees".

[sirhc55]

Then read this:

http://www.sekonic.com/classroom/classroom_2.asp

and wonder why ’professional’ studio photographers still use light meters and flash meters

[christiand]

Hi everyone,

a very interesting thread here.
The following thought crossed my mind:
based on what Matt. K was saying re camera metering being based on the 18% grey card assumption (please excuse my wording), would it make sense to manually meter with the camera once you understand (identify) the key area for measuring exposure for your tricky photos ?
I will investigate this theory and appreciate your thoughts on this.
Regards,
CD

[phillipb]

I would often take three or four incident readings from various parts of my subject, to ascertain how evenly the light was falling over that subject.

You know, last century, the likes of Olympus made cameras that could spot meter 5 or 6 individual places of your choice within the viewfinder and then average it out for you. Nowdays I don't see what all the fuss is about, just chimp and adjust exposure as needed on subsequent shots. Why spend $700 to get it spot on the first time when I can do the same thing for free in a couple of exposures.

[adam]

Actually I bought the lightmeter as a flashmeter to use with flash, because I don't think my camera's reflective metering works with the flash (have to trigger the flash when I meter)

iTTL basically does that for you. It sends out a couple of preflashes, evaluates the result and sets the duration of the main flash based on what it "sees".

I don't get TTL with the wireless radio triggers
and have that feeling of control when I don't use TTL

[Matt. K]

Patrick
You are correct. Metering and shooting off black or white will result in grey images. this is why you rarely see good quality imagery from the snow fields. Many beginners see the bright white snow and actually close down an extra stop or two thinking they are doing the right thing. They are simply making the problem worse. Grey, muddy snow.

[Reschsmooth]

They are simply making the problem worse. Grey, muddy snow.

Unless it's Thredbo

[sirhc55]

Patrick
You are correct. Metering and shooting off black or white will result in grey images. this is why you rarely see good quality imagery from the snow fields. Many beginners see the bright white snow and actually close down an extra stop or two thinking they are doing the right thing. They are simply making the problem worse. Grey, muddy snow.

Many beginners would know stuff all about closing down or opening up and would rely on the metering, which would be incorrect

[Matt. K]

Chris
I am refering to advance beginners.

[Oz_Beachside]

Mods, can we add this to Tips and Tricks, or even Tutorial, maybe on teh front page?

has a lot of value!!!

well done all contributors, and thanks

[gstark]

Bruce,

I'm in two minds on that: on the one hand, it is great advice, and I was thinking, before you made your suggestion, of making it a sticky.

But my reticence arises because we're discussing (primarily) hand held meters, which are not really the provenance of the majority of our members here. That's certainly not a final deciding factor for me, but it is a bit of a concern.

Maybe I need to convert it into a tutorial and hang it off the front page, except that it's not really a tutorial either.

See my dilemna?

[Oz_Beachside]

Bruce,

I'm in two minds on that: on the one hand, it is great advice, and I was thinking, before you made your suggestion, of making it a sticky.

But my reticence arises because we're discussing (primarily) hand held meters, which are not really the provenance of the majority of our members here. That's certainly not a final deciding factor for me, but it is a bit of a concern.

Maybe I need to convert it into a tutorial and hang it off the front page, except that it's not really a tutorial either.

See my dilemna?

since more members are starting getting studio lights, think there its lots of good in this content, perhaps a sticky in tips and tricks? might be a waste if this was lost in general discusison (oh, and can delete this post if moved, since off topic).

[Louie]

It would be good if this was somewhere easy to get to, esp. Matt's first post. I don't have any of this gear, light meter or otherwise, and have still found it helpful and interesting to read. My 2c