Dense person using light meter

David Calson · April 11, 2009

I own an HMC-150 camcorder, I think this has about 8 stops of latitude rated at 500 iso.

So here's what I do,

I set the meter to 500 iso, 1/50 shutter speed.

I press the button and then............................????

The meter will give me an fstop?

The meter will give me a footcandle amount?

I'm really dense and I've read alot of stuff but I still get very confused, the one article that did help get things a little clearer is here, http://www.cineobscure.com/dynamic-range-a...hting-for-film/

His explanation using footcandles seems clearer to me, I like things being explained in footcandles...

Let say this, I have a key pointed at subject, I meter the light and it says I've got 400 candles at 5.6, okay I set the camera to 5.6. So 400 fc is my midpoint, my highest point without clipping is 6400 fc, my lowest point 25 fc?

I guess the part I'm confused most about is what happens when I press the meter button, will it give an f/stop a fc amount or both...

Adrian Sierkowski · April 12, 2009

I don't quite get your question... some meters will read off in FC others in F stop (which is related to footcandles vs the ISO of the film) or others, like mine, in both.

So if you're at 20 FC on something that is 500 speed then you'd be at a F2.8, 400 would certainly not be a 5.6 at 500ISO! 80 would. 400 FC on a 500 speed film would be... something like and F11 F16 split. (every time you double the FC you increase 1 stop, so you also, to properly expose, close down the iris 1 stop, e.g. 2.8 (20FC), 4 (40FC), 5.6 (80 FC), 8 (160FC), 11 (320 FC), 16 (640 FC) . . .)

Now on video you don't really need to use a meter as much (I use mine for rought evaluation of lighting) because you have zebras and histograms in most cameras. Now, myself, I set my zebras at 80% (80IRE) and I try to keep "white" things there abouts. Then I'd want a white face to be around 60 IRE (60%) or a black face around 45IRE (45%). I can tell this off of the histogram, which is a line-graph of exposure from 0-100 or white to black. So, lets say I set someone up whose white for an interview. I can zoom into the face and look at my histogram. Ok, it is to the right of it's middle.. her skin (if i'm zoomed into an "average" area of light) is too dark. So I open up my aperature, or add more light, to nudge it a bit to the left of it's mid-point (50IRE) to get the skin where I want it) then I can zoom out and look around my frame for anything that's buzzing (zebra-ing?) and deal with that by bringing it's level down, or upping the exposure on the face (adding more light, stopping down). Hell on some cameras you can set 2 zebras, to say 60 and 90 IRE and the just use the one for Caucasian skin and the other for white.

Contrast ratio is key+fill:fill alone. You can do this in stops or in FC. I like to work in FC but some will do this in their head (converting the stops to FCs I suppose).

Ok so our film is 500ASA

Our Key (K)=40FC or an F4

Our Fill (F)=20 FC or an F2.8

so Contrast ratio = K+F:F, so 40+20:20, or 60:20. Now some simplification, 3:1

According to Harry Box, in his "Set Lighting Technician's Handbook," : For most normal situations, the contrast ratio is kept somewhere between 2:1 and 4:1. A three stop difference, 9:1 ratio puts the fill side in near darkness just barely leaving detail in the shadow area (pg 138-139

So, normally we'll be dealing with a difference of a few stops on either side (key v fill).

The meter is simply going to quantify the amount of light as either a stop or a FC amount. Stops are based on film speeds, but FC is just how much light there is. Then from this you can extrapolate your stops. Hope this somehow helps;

Saul Rodgar · April 12, 2009

I guess the part I'm confused most about is what happens when I press the meter button, will it give an f/stop a fc amount or both...

It depends what meter you are using. Some old analog meters will give you first foot candles and then you need to set the shutter speed and ASA dials right to get your f-stop. If it is a digital one, it should display f-stop or fc or lux or something on the screen next to the number.

Edited April 12, 2009 by Saul Rodgar

David Calson · April 12, 2009

Hey thanks for the reply guys, I'm pretty ADD so I will try and compute all that was said. Yeah with video you don't really need a meter, but I like knowing how to light without rechecking the monitor or wfm.

Adrian Sierkowski · April 12, 2009

Light by eye, not by meter.

Takes time to get there, but you get there.

I feel on video you need to light to the monitor a bit more than you do with film...afterall, mostly you'll be showing your video work on a monitor, not a film print.

David Calson · April 14, 2009

The meter is simply going to quantify the amount of light as either a stop or a FC amount. Stops are based on film speeds, but FC is just how much light there is. Then from this you can extrapolate your stops. Hope this somehow helps;

I see, so if the meter tells you an fstop and you know your film speed, you can also know the fc amount based on this or vise versa, it tells you a fc amount, you'll know what fstop you're at.

So is there like a formula or equation to go with this so that you can say, oh I have 300 fc at 500iso, that's an f/????

Adrian Sierkowski · April 14, 2009

If there is a formula, I don't know it off of hand.. essentially as FC double it is an increase of 1 F stop. So...

20FC is a 2.8 (form Kodak's site on 500 speed film), 40 is a 4, 80 is a 5.6, 160 is a 8, 320 is an 11, so 300FC would be just a little under F11...

This just comes from memory. Also, because film speeds double the same way, 80 FC on 500 is a 5.6, on 250 is a 4, on 125 is a 2.8 on 64 is about a 1.4

These are just numbers you'll get used to, kind of like shutter speeds and F stops in still photography, ya know?

David Calson · April 14, 2009

Alright now that I've learned so much from this thread, time to put the knowledge to the test...

I'm shooting on a 500iso camera, 8 stops of latitude, pull out the meter

*80FC*

Okay, I set the lens to 5.6

Here's my range of visiblity right?

5fc

10fc

20fc

40fc

*80fc*

160fc

320fc

640fc

1280fc

Adrian Sierkowski · April 14, 2009

Yes and no. That may be what your camera can capture; however what is "visible" will depend on the range upon which it can be shown.

Think of it this way. If I shot an image with 20 stops of latitude, but I display it on a 2 color black and white display.... what'll happen?

Also, different mediums will record differently. Film, I find, records more in the highlights (so maybe 4 stops over but 3 under for example) whereas video is the opposite, maybe 2 stops over but 4 stops under. It'll depend on camera and many variables, but you're getting the basic concept very well

Tom Jensen · April 14, 2009

I'm shooting on a 500iso camera, 8 stops of latitude, pull out the meter

1280fc

This is a common misuse of the term "latitude." Film has about a one stop latitude. This is the amount of over exposure and underexposure that allows you to get an acceptable PRINT. It might be greater now since I have not shot any film in a while. The 8 stops that you are referencing is the "Brightness Range." Many people think that film has more latitude than it does because many people shoot film and transfer it to video tape. The transfer is much more forgiving than the print.

David Calson · April 14, 2009

Also, different mediums will record differently. Film, I find, records more in the highlights (so maybe 4 stops over but 3 under for example) whereas video is the opposite, maybe 2 stops over but 4 stops under. It'll depend on camera and many variables, but you're getting the basic concept very well

Very true, well I'm glad to know I'm finally getting it now, thanks for the tutoring, one more question, when people say the key/fill ratio, by fill do they mean just the less brighter light hitting the main subject or would they mean any light in the scene that's not the key light (with exceptions of a kicker or anything brighter than the key). Thanks again really!!

Adrian Sierkowski · April 14, 2009

They mean just the fill light hitting the subject. Of course you will also want to meter and know where things in the BG will read, but for the key:fill ratio you're pretty much so just concerned with your subject.

David Calson · April 18, 2009

Alright, one more clarification, you have two 250w lights, two subjects at different distances from the camera. Both lights are lighting the subjects at the same footcandle amount, though subject A is 5 feet from the camera and subject B is 20 feet from the camera. Because the light reflecting on subject B has farther to reach the camera than subject A does that mean subject B will appear dimmer?

Tom Jensen · April 18, 2009

Alright, one more clarification, you have two 250w lights, two subjects at different distances from the camera. Both lights are lighting the subjects at the same footcandle amount, though subject A is 5 feet from the camera and subject B is 20 feet from the camera. Because the light reflecting on subject B has farther to reach the camera than subject A does that mean subject B will appear dimmer?

much

David Calson · April 18, 2009

much

I guess this is where inverse square law and a spot meter become your friend

David Mullen ASC · April 18, 2009

much

No, that's not correct -- if a foreground subject and a far background subject have the same number of footcandles hitting them each, they will appear as being lit to the same level. Objects don't get darker as they get farther from the camera, just farther from the light.

Now if the two 250w lights are next to each other, the one hitting the further subject would have to be spotted down to achieve the same footcandle level as the subject closer to the other 250w light.

Tom Jensen · April 18, 2009

No, that's not correct -- if a foreground subject and a far background subject have the same number of footcandles hitting them each, they will appear as being lit to the same level. Objects don't get darker as they get farther from the camera, just farther from the light.

Right, I misread the question. He did say "foreground subject and a far background subject have the same number of footcandles hitting them." They would appear smaller, I know that much.

Edited April 18, 2009 by Tom Jensen

David Calson · April 18, 2009

Thanks for the clarification David, I love this site, getting tutored from the best

Tom Jensen · April 18, 2009

Thanks for the clarification David, I love this site, getting tutored from the best

Not by me. :blink: David is one of the smarter, more talented DP's I know. He has the unique ability to speak clearly and in easy to understand terms.

Jim Hyslop · April 18, 2009

Not by me. :blink: David is one of the smarter, more talented DP's I know. He has the unique ability to speak clearly and in easy to understand terms.

Which is probably why he co-wrote a book on the subject :-D