Basic Light Meter Question

[Matt W.]

So I finally got a light meter and...I can't figure it out.

I'd learned to use an incident meter to expose for skin tones (which are apparently around 18% gray for caucasians)...and that's worked okay for me. This is my first "dualmeter," though and my readings are confusing.

When I use incident mode it tells me to expose about a stop brighter versus the reading I get on my skin when using the spot meter (metering the same part and using the hemisphere in the correct direction, facing the light). I repeatedly get this result, and the spot meter seems to offer the better reading (a stop under the incident meter).

Is this because my meter is mis-calibrated? I have relatively pale skin but not like unusually pale. I don't have an 18% gray card, but I'll buy one because I assume everyone will just tell me to.

Edit: And is it normal that I have to push kind of hard to turn the wheel from incident to spot? It's a sekonic.

 

[David Rasberry]

The readings should match on an 18% gray card. With the spot meter you measure the reflected light value which will vary with the reflectance of the surface you are measuring. Also the flat incident disk should get the closest match to an 18% gray spot reading when held parallel the surface of the gray card facing toward the light.

 

[Matt W.]

Thanks, I'll buy a gray card tomorrow and try that out.

 

[Dan Hudgins]

90% to 18%

90% to 18%

The reflected reading for the 90% side should be 2.5 stops higher than the 18% side of the Kodak Gray card, Kodak has a new "Gray Card Plus" also. Spot meters can make you push the exposure way off, using dome pointed at the camera can give more consistent results, and help check the kicker to fill ratio by turning the meter around and pointing the dome at the lights.


These links may help people that cannot match their light meter to the RED ONE exposure,

http://www.bythom.com/graycards.htm

http://www.richardhess.com/photo/18no.htm

Here is a link from kodak about how to use the gray card,

http://motion.kodak.com/US/en/motion/Products/Lab_And_Post_Production/Gray_Card/cinematographer.htm

And about the Gray card plus,

http://motion.kodak.com/US/en/motion/Products/Lab_And_Post_Production/Gray_Card/index.htm

when you grade your images the gray card should read 117/255 for 8 bit displays, or about 0.458 signal for other bit depths in gamma 2.2 images.

the sensors in some meters are red bias and will read skin lighter than they should, more so under tungsten lights because the cell in the meter may read IR as well, so its best to use the dome, or point it a the 90% or 18% gray card. The 90% side of the card shoud read about 33% signal on the linear light histogram.

 

[David Rasberry]

I use an incident meter only along with the TTL metering in camera. I typically take at least three readings with the dome. One towards the primary key light, one towards camera, and one faced away and shaded from key to get the background ambient. If there are practicals in the scene I will read them from a foot or so away. The range of these readings establish the dynamic contrast range of your scene illumination. I then choose exposure settings by eye from experience based on Ansel Adams Zone methods. This has worked well for me with both film and video cameras, but you have to know the DR characteristics and practical ISO rating of your chosen medium well.

 

[David Mullen ASC]

It's basic: an incident meter reads the amount of light falling onto the object, a reflective (spot) meter reads the amount of light reflecting off of the object.

Just two different things. The incident meter doesn't care what the object is, dark or bright-toned, it just tells you the amount of light falling. A spot meter assumes that the object is 18% grey in reflectance (more or less) so you have to creatively decide what tonal value you want to give your subject relative to 18% grey. For example it is not uncommon to decide that caucasian skin tone should be one-stop lighter than 18% grey in full exposure. But creatively, you may decide differently.

When you are lighting a set, usually you use an incident meter to set levels -- for example, if you want a series of keys or spots throughout the room to read at f/2.8, regardless of what objects pass through those areas. Or you can use a spot meter but you'd need a grey card to read off of.

Now with an incident meter, there is also creative decisions to be made when you want things to be brighter or darker.

So there is no right or wrong meter to use, it's partly a way of thinking, a way of working that works for you. I tend to use incident meters for spaces contain multiple objects of varying tones, and spot meters to check for individual elements and how bright they are.

 

[Matt W.]

Cool, this makes tons more sense now. I know the difference between an incident meter and spot meter in terms of function; I've just never been sure how to use them together for the best results and I (for some reason) assumed caucasian skin was closer to 18% gray than it is. So far my gray card seems to match the incident meter, which is a relief. Of course like the incident meter is the most useful for like motion picture work (and when I shot 16mm a few times it's all I used), but I really dig the spot meter so far for landscapes and ratios. Knowing that bark, brick, and blue sky are all around 18% gray (in theory) provides a decent basis for exposing without having to bring a gray card everywhere (but usually I just shoot based on the incident reading).

I think I'm just going to shoot a lot of film and see how it responds. Is it possible to buy motion picture stock for still cameras, btw?

 

[David Rasberry]

Cool, this makes tons more sense now. I know the difference between an incident meter and spot meter in terms of function; I've just never been sure how to use them together for the best results and I (for some reason) assumed caucasian skin was closer to 18% gray than it is. So far my gray card seems to match the incident meter, which is a relief. Of course like the incident meter is the most useful for like motion picture work (and when I shot 16mm a few times it's all I used), but I really dig the spot meter so far for landscapes and ratios. Knowing that bark, brick, and blue sky are all around 18% gray (in theory) provides a decent basis for exposing without having to bring a gray card everywhere (but usually I just shoot based on the incident reading).

I think I'm just going to shoot a lot of film and see how it responds. Is it possible to buy motion picture stock for still cameras, btw?

Some years ago there was a lab that loaded Kodak movie stocks into 35mm canisters and sold them with processing included in the price. Haven't seen any magazine ads for this service in a while though. Might find an ad in a copy of American Cinematographer if you can find a recent one. Bookstores no longer carry it in my area unfortunately.