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I have a few general questions about cinematography


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#1 Jose Eulalio Tapia

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Posted 04 December 2010 - 11:06 PM

Im a student of filmmaking and im interested in cinematography, there is a lot of questions (basic questions) that i have to make about this, and im doing those questions here because my teacher in the college isnt is very good (im in a cheap college because of money, and isnt is very good), well here are the questions, please answer me. (Sorry about my english).

1- A good Director of photography have to know ALL the techinchal information that have the Gaffer or the techinicians in general?

2- In a small project on 16mm, the ISO of the film was 500T and we needed to film a few shots in exterior, so we used a 85 ND9 filter on the camera (and f 5.6) but i didint understand why, instead, we just close the diaphragm to f16, we needed depth of field so i told that to the teacher and he said "yeah if we have a f16 we will have a lot of depth field but that isnt is favorable because it will push the film" and then he just evade my other question so i didint understand why the f16 "push" the film if enters the same amount of light that with the filter ND...

3- Exist a H&D curve for video?, i have a Nikon D90 (provided) for a week so i want to make a short but i dont know the limits of exposure that have, and i dont know how to "gauge the light", i really dont understand video very well.

4- There is a great difference of cuality betwen an analog light meter and a digital one?
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#2 David Mullen ASC

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Posted 05 December 2010 - 02:01 AM

Im a student of filmmaking and im interested in cinematography, there is a lot of questions (basic questions) that i have to make about this, and im doing those questions here because my teacher in the college isnt is very good (im in a cheap college because of money, and isnt is very good), well here are the questions, please answer me. (Sorry about my english).

1- A good Director of photography have to know ALL the techinchal information that have the Gaffer or the techinicians in general?

2- In a small project on 16mm, the ISO of the film was 500T and we needed to film a few shots in exterior, so we used a 85 ND9 filter on the camera (and f 5.6) but i didint understand why, instead, we just close the diaphragm to f16, we needed depth of field so i told that to the teacher and he said "yeah if we have a f16 we will have a lot of depth field but that isnt is favorable because it will push the film" and then he just evade my other question so i didint understand why the f16 "push" the film if enters the same amount of light that with the filter ND...

3- Exist a H&D curve for video?, i have a Nikon D90 (provided) for a week so i want to make a short but i dont know the limits of exposure that have, and i dont know how to "gauge the light", i really dont understand video very well.

4- There is a great difference of cuality betwen an analog light meter and a digital one?


A DP has to know enough to do his job, but he doesn't have to know things to the same degree and depth as the experts he hires -- he doesn't have to know the color-correction system as well as the colorist but he has to know the fundamentals of electronic color-correction; he doesn't have to know electricity as well as an electrician but he has to know enough to make the right decisions about equipment, manpower, etc. though of course he will consult his gaffer; he doesn't have to know everything about lab chemistry to the level that he could process the film himself, but he needs to know the main issues involved.

Well, an 85N9 is a 3 and 2/3-stop correction, not just 3-stops. Why not shoot at f/16 instead of f/5.6? The main reason is the way that it makes the image look, you obviously have more depth of field at f/16. Maybe that would be the correct look for the scene, maybe not, that's partly a filmmaking decision based on the intent of the shot. But you don't just shoot at f/16 because it's easier to not use a filter, that's just being lazy, the whole idea is to CONTROL the image, and controlling depth of field is one aspect to control.

From a technical standpoint, there is some loss of sharpness when you are too stopped down due to diffraction. Lenses tend to work their best in the middle of the scale, or at around two-stops closed from wide-open.

There is also the perception that the contrast gets harder, higher when stopped down. Actually, it doesn't, but because more of the image is in-focus due to the higher depth of field, you see the hard shadows in both the foreground and the background, whereas when areas get thrown out of focus, they feel lower in contrast because you've blended the highlights and shadows into a blur. Look at a waveform monitor at a high contrast shot and then throw the image out of focus... you'll see that more of the information ends up in the middle of the IRE scale, though the highs and lows remain.

H&D curves are basically gamma curves... a video sensor responds to light in a linear fashion, not in a curve, but gamma curves can be applied to a video signal -- knee compression at the top, black stretch at the bottom, will sort of bend the straight line response into a crude s-shape curve.
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#3 Jose Eulalio Tapia

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Posted 05 December 2010 - 08:45 PM

A DP has to know enough to do his job, but he doesn't have to know things to the same degree and depth as the experts he hires -- he doesn't have to know the color-correction system as well as the colorist but he has to know the fundamentals of electronic color-correction; he doesn't have to know electricity as well as an electrician but he has to know enough to make the right decisions about equipment, manpower, etc. though of course he will consult his gaffer; he doesn't have to know everything about lab chemistry to the level that he could process the film himself, but he needs to know the main issues involved.

Well, an 85N9 is a 3 and 2/3-stop correction, not just 3-stops. Why not shoot at f/16 instead of f/5.6? The main reason is the way that it makes the image look, you obviously have more depth of field at f/16. Maybe that would be the correct look for the scene, maybe not, that's partly a filmmaking decision based on the intent of the shot. But you don't just shoot at f/16 because it's easier to not use a filter, that's just being lazy, the whole idea is to CONTROL the image, and controlling depth of field is one aspect to control.

From a technical standpoint, there is some loss of sharpness when you are too stopped down due to diffraction. Lenses tend to work their best in the middle of the scale, or at around two-stops closed from wide-open.

There is also the perception that the contrast gets harder, higher when stopped down. Actually, it doesn't, but because more of the image is in-focus due to the higher depth of field, you see the hard shadows in both the foreground and the background, whereas when areas get thrown out of focus, they feel lower in contrast because you've blended the highlights and shadows into a blur. Look at a waveform monitor at a high contrast shot and then throw the image out of focus... you'll see that more of the information ends up in the middle of the IRE scale, though the highs and lows remain.

H&D curves are basically gamma curves... a video sensor responds to light in a linear fashion, not in a curve, but gamma curves can be applied to a video signal -- knee compression at the top, black stretch at the bottom, will sort of bend the straight line response into a crude s-shape curve.


Thank you very much David, the ansewrs helped me a lot i really apreciated it.
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Willys Widgets

Aerial Filmworks

Visual Products

Glidecam

Opal

Tai Audio

Rig Wheels Passport

Metropolis Post