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I think it's a bit of a generational thing... Younger people who like digital images prefer less noise and don't mind the clipping, whereas older cinematographers who worked with film don't mind some noise (which is still lower at 800 ISO on the Alexa than the grain of 200 ISO film) but want to avoid clipping and want to emulate the long roll-off to white for overexposure that film negative has, which is one reason the Alexa is so popular.

 

To me, to be blunt, film negative tended to fall off in the shadows quickly into grain but hold a lot of detail into overexposure, while digital has traditionally been the opposite, lots of useful shadow detail but you lose the highlights faster. So one way to get digital to look more like film was to lose some shadow detail and extend the overexposure detail.

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First I'd like to point out I don't advise changing the aperture for every setup like a madman.

 

This reminded me of something… I often read about how an entire film was shot at one aperture or how there were maybe three aperture values for the whole film or something. So I’d like to know is that how it’s done: you pick an aperture and then you go on to set up the lights so that with that aperture value you will have the desired exposure? It somehow seems it should be the reverse, but there’s surely a reason for this. And second question: what happens with the camera’s aperture when there’s a tracking shot following a person through varying degrees of illumination?

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I was always told, during the film days, it was pretty typical to pick an F stop, ISO and light everything to it, trying hard to keep the same exposure throughout. It's a wise idea because it saves you a lot of time and aggravation in post. However with the digital workflows we have today, post is a pain no matter what you do. So it really doesn't make any difference if you constrict yourself, in fact I bet nobody will let you on a modern shoot.

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You more or less light to a desired aperture for optical consistency in sharpness and depth of field, but most cinematographers are pretty flexible about that. Maybe you aim for an f/2.8 but end up at an f/2.8-4.0 split... It's no big deal. And it is not unusual to work at a higher stop for day work and a wider one for night work, some believe that looks natural for day scenes to have more depth of field.

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Yes, in the days of photochemical printing, you couldn't fix contrast and sharpness mistakes so you worked harder to be consistent. Today, no one sweats tossing in a lens that has less contrast now and then because matching is so much easier in digital color-correction. Even Darius Khondji used to go through elaborate hoops to match contrast by using a Varicon flashing device and pulling or pushing different stocks, etc. and then combining this with silver retention printing tricks... but now you don't hear him doing so much of that.

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Two questions: is that VariCon thing something people are taught in film school during a cinematography (under)graduate course?

 

And two, so tracking through a piece of space with varying degrees of illumination doesn’t really matter because the aperture stays the same? For example, if you step from a fairly faint interior through the door into harsh midday Sun?

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"Stop-pulling" has always been done when necessary especially on location in available light, but if you are lighting a space, it is less necessary since you can balance to the stop you want.

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At 24fps, 180 degree shutter, the exposure time is 1/48 sec. Same for film or digital.

 

Questions like this are probably better asked in the Beginners/Students forum.

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A film camera has a spinning metal disc in front of the gate, usually a half-circle (180 degrees out of 360 degrees) so the frame is exposed for 50% of the time it is in the gate, the other half of the time is used to advance the film to the next frame when the shutter is closed. So at 24 fps, the shutter time is 1/48 if the shutter angle is 180 degrees.

 

While a few digital cameras have a physical spinning shutter (usually because they have an optical viewfinder like the Alexa Studio does or the D21 did, so they need a mirror shutter), almost all digital cameras have electronic shutters (global or rolling) instead and thus can do things that a film camera cannot, like have a virtual 360 degree shutter angle, i.e. no shutter at all, so you can get 1/24 at 24 fps. However, the more you increase the shutter time over what a 180 degrees gives you in a film camera, the more motion blur you get and depending on how much motion is in the frame, the smeary motion can look very un-film-like.

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Another thing that separates digital from film when it comes to a shutter is that film projection doesn't leave a still frame on the screen for 1/24th of a second, like digital. So there is more flicker that goes along with film projection that isn't present in capture.

 

CMOS and CCD imagers pulse data down a bus to a processor, it's not a "direct" stream of information. All of the control on a digital camera is done POST the imager itself. We have zero control over the physical imager, unlike film where the imager is the film stock.

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Another thing that separates digital from film when it comes to a shutter is that film projection doesn't leave a still frame on the screen for 1/24th of a second, like digital. So there is more flicker that goes along with film projection that isn't present in capture.CMOS and CCD imagers pulse data down a bus to a processor, it's not a "direct" stream of information. All of the control on a digital camera is done POST the imager itself. We have zero control over the physical imager, unlike film where the imager is the film stock.

Not sure that matters so much, most people don't have control over the film stock any more than the sensor, the stock is made by Kodak and our control over it happens in post as well because processing happens in post and being a negative-positive system, it had to be transformed to a positive image, either electronically or by making a print -- again, all of which happens in post. So what control over the film stock that doesn't happen in post are you referring to? There is exposure and filtering, but those affect sensors too. You could flash the negative to lower contrast but a sensor can be flashed too, so I'm not sure what you mean by saying we have zero control over the sensor but we have control over the film stock -- unless you simply mean we can load different film stocks into the camera.

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Two questions: is that VariCon thing something people are taught in film school during a cinematography (under)graduate course?

 

And two, so tracking through a piece of space with varying degrees of illumination doesnt really matter because the aperture stays the same? For example, if you step from a fairly faint interior through the door into harsh midday Sun?

I read about the Varicon in American Cinematographer and learned more about it here from David. Never heard about it at film school.

 

The beauty of light is in its variation. Most of us try to build in areas of light and shadow by creating pools of light that the actors can walk in and out of. For times when you have no ability to control an extreme variation of dark to light, you can perform an iris pull and physically change the aperture in shot.

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I read about flashing techniques, including the Panaflasher, Lightflex, and Varicon, mainly in American Cinematographer. The Varicon was a redesign of the Lightflex and by the time it came out, flashing had fallen off in usage (and it never was all that common.) I used the Panaflasher on four features in combination with a silver retention print process. Never got to use the Lightflex or Varicon.

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