Incident meter, how does it work?

[Matthew W. Phillips]

 

Not saying it's impossible to communicate all the complexities and caveats in a (very long) post or two, just saying a forum such as this certainly can afford half-arsededness ;) where we can call BS on parts of someones argument, then in turn skirt over complexities of our own (aware or not).

Not sure what you are trying to say. However, I stand by thinking jecl ark is wrong in thinking that kodak neg can only handle 2 stops over exposure before falling apart. too many camera tests and charts have been shot to prove that as rubbish. V3 has quite a bit of latitude. Not unlimited but enough to where one would have to be mighty careless indeed to feel "Aww shucks, this footage is unusable!" Compared to most of the camera systems being used by people on these forums (digital) I would take my chances with V3 anyday.

[Chris Millar]

Not sure what you are trying to say.

 

Exactly B)

[David Mullen ASC]

Kodak color negative can handle more than 2 stops of overexposure and be pulled back -- that's only, what, about 12 printer light points? If your negative normally prints around the 30's and you had one shot that had to be printed at the mid 40's, that would work fine. I once got back a second unit shot where they accidentally used 500 ASA film when they thought they were using 50 ASA film and thus overexposed the image by a bit over 3 stops and it could be printed back down to normal, though I ended up in the high 40's with that shot. But even if you top out at 50, you could re-trim the printer if needed to print down a bit more.

[John E Clark]

Kodak color negative can handle more than 2 stops of overexposure and be pulled back -- that's only, what, about 12 printer light points? If your negative normally prints around the 30's and you had one shot that had to be printed at the mid 40's, that would work fine. I once got back a second unit shot where they accidentally used 500 ASA film when they thought they were using 50 ASA film and thus overexposed the image by a bit over 3 stops and it could be printed back down to normal, though I ended up in the high 40's with that shot. But even if you top out at 50, you could re-trim the printer if needed to print down a bit more.

 

Would that be the 5219 Vision 3 stock? And how is it for 'under exposure'?

Edited June 10, 2014 by jeclark2006

[Matthew B Clark]

To me it's really this simple: if I go out with a few rolls of color reversal, I will be sweating balls. If I go out with a few rolls of negative, I will not be sweating balls. I do not have a chart for this, but I do have several pairs of underwear that have logged the results.

[Matthew B Clark]

To me, that's latitude.

[Hongji Wu]

OMG, after 6 months this thread seems to become a battlefield... B)

Anyway, thank you all for the response!

[Hongji Wu]

 

Yes and no. There does not have to be a mid gray tone (commonly called the “key” tone) in the scene to expose for. This is a complicated subject. The key tone, or mid gray because it appears in the middle of a photographic gray scale, is the common reference point used by light meters, lab processors, and transfer colorists. A lab processor knows what density his processed emulsion should be to render mid gray and so he is able to adjust his processing accordingly. A transfer colorist, knows gain will reproduce the luminance of mid gray so he is able to set his gain. Simply put it is the reference point to which we peg all other values on the characteristic curve of the film or digital format we are using. Meters are likewise calibrated for mid gray. For example there are basically two types of meters: incident and spot. Incident meters read the light falling on your subject. Spot meters read the light reflecting back from your subject. An incident reading gives you an exposure that after normal processing would render an 18% gray card as 18% gray (a specific density of the film) had you held it in front of the camera in the same light. Incident meters enable you to peg the key tone (18% gray) in this fashion even though there may not be a mid-tone in your scene.

 

A spot meter is then typically used to take reflective readings to see how other objects will expose relative to the key tone that was pegged with the incident meter. The thing to remember about spot meters is that they want to expose everything as mid gray. For instance, if you expose a black piece of paper with the reading of a spot meter it will appear as mid gray after normal processing (not pushed or pulled) – likewise for a white piece of paper. But, if you place an incident meter down on the black piece of paper and expose for the incident reading the black paper will be black, and the white paper will be white, after normal processing because you exposed for the key tone by using the incident reading and thereby pegged the other values (white and black) relative to it. If you don’t have an incident meter, but want to peg the key tone under your subject's key light, an old trick is to take a spot meter reading of the palm of your hand under the key light and open up one full stop. This will give you a close approximation because the average Caucasian flesh tone is one stop more reflective than 18% gray.

 

 

(The “Characteristic Curve” of a high contrast B&W Reversal emulsion. The object of exposure is to place the contrast range of the scene on the straight line portion of the curve so that the different luminances of objects in the scene are reproduced accurately on the film. Mid gray being the common reference point.)

 

You use the reading from the spot meter to be sure that the object you are metering will be within the exposure range (characteristic curve) of the film stock you are using. If the stock has a nine stop range (five stops over before detail burns out, and four stops under before detail blocks up), and your reading of a dark object is six stops under your key tone, it will not be rendered on the film after it is processed normal (to reproduce mid gray as mid gray).

(The contrast range of this scene exceeds the film’s exposure range, so when the image is exposed for the light outside the arch (Left Image), detail is lost in the archway. Likewise, if the image is exposed to hold detail in the archway (Right Image), detail is lost outside the arch. Pegging the key tone centers the contrast range of the scene on the straight line portion of the curve such that some detail is lost outside and inside the arch way, but the luminance values of most of the scene are rendered accurately in the middle image.)

 

Since in this situation the contrast range of the scene is beyond the exposure range of the film you have two choices. 1) You can open up and expose for the shadows (over exposing the key tone and blowing out your highlights more in the process) and print down to make mid gray mid gray again. In the end you have the detail in the shadows you want, but in the process you have lost detail in the highlights. Why? Because the contrast range of the scene was beyond the exposure range of the film, and you exposed for shadow detail, you burned out the highlights (no detail) so it is not there when you print down to mid gray. You can't bring it back. Is that bad - not necessarily. It's just another "look."

 

(The contrast range of this exterior exceeds the exposure range (flat line portion of the “Characteristic Curve”) so shadow details, in his hair and the black velour under the MacBeth Chip Chart, that fall on the bottom of the ”toe” of the curve “block up” (max density) and detail in that area of the frame is lost. Likewise, highlights like the specular sun on the windshield and the white towel, that fall on the upper end of the “shoulder” of the curve “burn out” (min density) ) and detail in that area of the frame is lost. The object of lighting is to compress the contrast range of the scene so that it fits on the straight line portion of the curve so that the different luminances of objects in the scene are reproduced accurately on the film.)

 

Or, 2) you can throw some light into the shadows to bring the reflective value of the dark object within the exposure range of the film (onto the straight portion of its’ characteristic curve) without changing the exposure of the key tone value (mid gray) or blowing out the highlights. In this fashion you fit the contrast range of your scene into the exposure range of the film emulsion you are using. Of course this is only the starting point. From this “correct” exposure a DP will further manipulate the relationship of the contrast range of a scene to the exposure range of the film stock to create a desired effect. This is old school film exposure theory, but it is a good conceptual frame work for exposing digital video, especially now that you can record "raw" and apply "looks" to the raw data.

 

(Post in this thread the problems in this image and how to fix them)

 

A fun exercise is to shoot a frame with just available light and then think about how you can improve upon it through lighting. For example, identify the problems in the image above and then list how to fix them through lighting and wardrobe.

 

Guy Holt, Gaffer, ScreenLight & Grip, Lighting & Grip Sales and Rentals in Boston

Thanks for the contribution，Guy！I actually understand the logE curve, but you've still done a great job for explaining it in details! the mid gray doesn't need to exist in the actual scene and can be imaginary. 6 months ago I was so messed up in my brain... :)

Edited June 12, 2014 by Hongji Wu