Why do my light meters both give different readings to my cameras?

Question

I have two light meters - one is Boots and the other is Western III, for 200 ASA and 250th they both advise f4, but my two SLR cameras both advise f8 - I trust my cameras because they both give excellent photos, and it also makes sense in my estimation of light levels, so why the big difference? There are no batteries in the light meters.

Admittedly it was indoors looking at a sunny window, so they may have been confused. Just tried them now in a different situation and they're much closer to the camera meter.

Answer 1

Since your two handheld meters give the same result they seem to be working fine. The fact your two in-camera meters give the same results also means they are working fine. How can they both be correct? You were pointing the cameras at something two stops brighter (like a white wall, or sunny window like you mention) and taking a "reflective" measurement, while the handhelds were measuring the "ambient" light (I guess they have a kind of diffuse dome on them).

To understand why, you need to know that light meters are calibrated against "middle grey" - a particular shade of 18% grey - thought to be average (neither too dark, nor too bright). White objects reflect more light, dark objects reflect less. The meter in your camera doesn't know anything about colours so it just assumes everything is middle grey. If you point it at a white wall, it will assume it's really a grey wall that happens to be illuminated by more ambient light. Point it at a black wall, and it's that same grey wall in a dark room!

So if you want to check your camera's meter you need to point it at a middle grey object, like a grey card. If you don't have a grey card, the palm of your hand, or green trees are said to be decent substitutes. Just remember to fill the frame with your grey card (hand, etc.) and you should get more-or-less the same reading from your handheld and in-camera meters.

See my answer to this question for more details:
http://answers.yahoo.com/question/?qid=20060920172713AAvkSMw

Just remember that photography is an art; so there really isn't any "correct" exposure. If you want to take a spooky Halloween photo, you may want to "underexpose" so everything looks dark and gloomy. Once you understand how your meter works you'll be able to have fun controlling exposure to get the creative effect you want!

Answer 2

The cameras are reading from a designated area of your scene. It will be a tightly defined central spot, larger center-weighted, or programed average reading ("Matrix," etc.). You choose from these meter patterns based on the lighting and the subject. A spot meter can read a very tightly restricted area and ignore the rest of the field. A matrix reading will average the overall scene, but some upscale cameras have a number of pre-programmed "scenes" in memory to compare your situation to and they adjust the light according to the closest program. It usually works.

The meters are measuring the light wherever you point them. You may have noticed a clip-on diffuser or a rotatable diffuser dome with your hand-held meters. If you take an "incident light" reading, you use the diffuser and you just aim the light meter in the approximate direction of the light source. If your subject is some distance away from you, you just point the meter over your shoulder and see what it says. (Okay, you are allowed to turn around and face the light instead of pointing the meter over your shoulder...) If you take a "reflected light" reading, you do not use the diffuser. You would need to be able to get closer to your subject to do this. Place the meter very close to the key element in the scene and see what it says. If your scene is fairly evenly lit, you are likely to find that both incident and reflected readings are very similar, if not identical. Not all of the light the strikes your subject will be reflected. This is why you need to use the diffuser if you are not taking a reflected light reading. The diffuser will cut a stop or two from the suggested reading.

You read above about 18% gray cards, so I won't repeat that.

In any event, I think this may be more a matter of proper technique and interpretation than disagreement. If you use the light meters as they are really designed to be used, I'll bet your meter readings come much closer to your camera readings.

Answer 3

May be the light meters are reading light for an angle wider than that your two SLRs are measuring. The light measurement in cameras is for a portion of the frame. Usually center weighted unless you set it for point metering. So depending on the light coming from the source and the angle f the shot, I am nt surprised that you have different readings.

Check out what was the zoom/focal distance of the lens (thereby get the angle of view and note that the angle where the light metering s done s less than that).

Answer 4

light meters in a camera measure through the lens while the hand held one doesn't.
Lenses are coated and if you have a UV, skylight filter attached than those numbers get messed up... I would trust the cameras meter most of the time but when dealing with a back light you take the reading from the subject not the average total

Answer 5

Light Meters respond differently to Different Lights and Light Sources!
I take an Average then add +1 Stop(For general Photography)

For Exact measurement step to the subject with Both Light Meters and see what they say!(Normally Subtract 1 Stop!)
It's all about experimentation with Light and Photography!
Play with it!

Answer 6

Your camera is reading through the lens and will be reading from the area in the viewfinder, it may even be set on 'spot' and therefore only measure a certain area. I would go with the camera, assuming that it is in fact accurate, you can always bracket exposures and judge the results.

Answer 7

If you are really concerned, just take two extra shots one stop either side.
It took me a while to change over to digital but life is so much easier now.
I do miss my SLRs though and the quality is still much better.