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Establishing a shooting stop, then changing it with compensations.


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#1 Steven Carubia

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Posted 14 January 2012 - 07:46 PM

In Reflections: 21 Cinematographers at Work, Laszlo Kovacs stresses that, "Different T-stops will record an image differently, even if the scene is lit under similar conditions...I always predetermine the stop and maintain it for every shot in the scene. When you change a stop during the scene [especially at 500 ASA], a lot of the ambiance is changed, the film starts reading things that weren't there at the other T-stop, and vice versa.

I have been under the assumption that one could light to a deeper stop such as 5.6, thus granting the freedom to open up for shots where a shallower depth of field is desired, while compensating for the extra light with ND filters. I am fairly inexperienced and had not considered this a topic for examination. I'm sure results vary among different lenses and filters.

Laszlo describes a situation contrary to my own yet equally relevant. He speaks of the detrimental effects of shooting at a stop such as T4 and then closing down to 5.6 for a close-up; via doubling the light in the scene. He writes, "...sometimes there's so much bounce light that some of the fill starts to bleed into areas that you don't want recorded."

I would love to hear what the professionals among us have to say about shooting stops and deviating from them by the means described above.
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#2 Tom Jensen

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Posted 15 January 2012 - 01:04 AM

In the article you sighted, Kovacs is referring to interiors. A couple of factors come into play. First, because of the advent of faster and better film, you don't need the amount of light that you did in the past. Sets get hot, make up melts, people squint and it is generally uncomfortable. So it's often advantages to shoot with the least amount of light that you need to light the set the way you want. Secondly, a lens performs optimally, in most cases about 2 stops closed from wide open so generally people shoot around a 2.8. That gives you both a nice shooting stop and a lens that is performing optimally. If you start to stop down you increase depth of field which is not necessarily what you want when shooting on a set because you a generally concentrating on a actor, sets sometimes have imperfections and for whatever reason, the wider stops just look good to the eye. You want the actors to stick out and be separated from the background at this stop. Your stop won't change that much once your lit. You light your master to your shooting stop and then you clean up your lights on the close up meaning you make small adjustments. You might bring in some fill light, add a back light, soften a key or add a hairlight or an eye light. What you don't want is to light your master to an 8, shoots your closeup at a 22, shoot an medium shot at an 11. It just doesn't make sense, it doesn't look good, it gets hot and like Laszlo said, light starts bouncing around. Your depth of field is going to change when you change lenses and when you change subject to lens distances but they really don't change the overall look of the film. A consistent stop helps the lighting look consistent. There are times when you want to shoot a little deeper on Longer lenses to help the assistant stay in focus but usually by a stop. There will also be times when you need to shoot wide open because you just don't have the light and those shots will look different. Not normally to the untrained eye but to the trained eye they will.
ND's are for exteriors. Even outdoors you don't normally want to shoot stopped way down because you still want the actor to be somewhat isolated but you aren't usually hampered by the background being so close like on a set so you can shoot at a 4 or 5.6. If you put too much ND in front of the camera, you can't see anything. On vistas and wide shots you can shoot a little deeper because the subject is now the background and that is what you want to see in focus. Exteriors are often difficult to shoot because the sun moves and clouds block the sun, there are long shadows often a lot of contrast. You shoot exteriors with a large crew with lots of equipment that help you keep the light consistent or you have the exact opposite where you have no crew, limited equipment and you just have to get what you can and try to keep the stop close but it doesn't always work. When you have a big crew you can keep the lighting consistent but as the sun goes down the background gets darker and your actors start to look lit. Then you have to pull the ND's, then open up the lens and decrease your foreground light levels to keep it consistent. The stop changes but you really have no choice. The set gives you the most control and the more control you have the more consistent the footage will look. Hope this clarifies some things.
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#3 David Mullen ASC

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Posted 15 January 2012 - 09:34 AM

I'm not too pedantic about the shooting stop -- I first light the set, balancing to windows, practicals, etc. I often aim for an f/2.8-4 split inside partly because in TV work, I'm using zooms which need an f/2.8, but also I'm not fond of shooting at f/2.0 or wider unless for a specific effect or where I need to balance with dim natural light. It's not that I don't like the shallow focus look, it's just that it's not practical when you have a fast schedule and can't give the focus-puller a lot of takes to get to right.

Lately I've been using ND filters inside because of the speed of cameras like the Alexa, at 800 ASA and higher -- I find that when I'm done lighting, I'm closer to an f/5.6 and prefer the look of being closer to an f/2.8. But since the B-camera often has a 11:1 Primo zoom on it at 200mm-ish to grab some close-up, I find that shooting the camera with the wider lens at f/2.8-4.0 but the longer lensed camera at f/4.0-5.6 actually makes the depth of field look more similar -- if anything, the longer-lensed close-up still looks shallower in focus than the wider shot even if stopped down. I noticed that the other day outside in a park where I had the medium shot at 75mm and the close-up at 200mm at the same time, and had 2-stops more ND in the wider camera... though the tighter camera was stopped down 2 more stops, the background was still more out-of-focus than with the wider camera. So the notion that always shooting at the same stop gives you more consistent depth of field doesn't take into account the visual aspect of focus.

But in terms of contrast, ambience, etc. there are a lot of reasons to light to a f-stop like f/2.8 or f/4.0 in general because it does affect how much natural ambience is recorded. To some degree you have to decide how much natural ambience you want to preserve versus overpower or block out.
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