Film vs. Digital

[Stevie]

Could someone please describe the difference between Film cameras and Digital cameras, and in technical terms how EXACTLY each of the two work. I need facts please.

thanks.
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WASHINGTON MEDICAL MARIJUANA

 

[David Mullen ASC]

To avoid typing in a textbook-worth of information, as well as to avoid telling you what you already know, could you narrow the question a little? First start by telling us what you understand what the differences are. I mean, I could write a chapter on just how color negative emulsion works but I don't think you want to read it...

Are you asking what are the essential visual qualities of a film image and a video image and why those qualities exist? Or do you really want to know how film emulsion works, the difference between negative and reversal, how release prints are made, how film is color-corrected, how a film camera shutter works, how reflex viewfinders work, types of camera motors, the history of the 24 fps frame rate, how a CCD works, how digital recording works, about compression, color-sampling, etc.?

 

[Stevie]

I know about shutters, iris, and some others about film, however, i am writing a report and i just need to know the bare basics about what a CCD is and what it does(Brief). How is film developed(brief). Different types of film cameras, I know about DV. I need to know about the essential visual qualities of a film image and a video image and why those qualities exist.
Mere basics please. Thanks.

-Stephen
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Sally_foryou

 

[David Mullen ASC]

This is still too broad for a forum question. Do you really think this can be answered in a couple of paragraphs? And some of this can be looked up easily with Yahoo! or Google. For example, have you tried searching under "DEFINITION CCD"? And definitely there are textbooks on these subjects; you aren't seriously going to quote an internet forum post as a source in a paper?

An internet forum is better at explaining something specific that is still unclear to you, after you have done the basic research. It's more of a last resort than a first stop. There may be whole websites out there with basic diagrams showing a camera shutter or a CCD prism block, or the layers of film emulsion, etc.

For example, try:
http://www.kodak.com/US/en/motion/

For a lot of info on film technology.

 

[David Mullen ASC]

As for the film look issue, you have to first begin with the understanding that most film is shot at 24 fps, sometimes 25 fps (for PAL television), and rarely 30 fps (for NTSC television when a 3:2 pulldown is to be avoided.)

The shutter in a film camera is normally a spinning disc, usually a half-circle (called a 180 degree shutter angle) that uncovers the film in the gate to expose the frame, then covers it so that the movement can advance the film to the next frame, ready to then be exposed. So if the camera is running at 24 fps with a 180 degree shutter, the exposure time (shutter speed) is 1/48th of a second. So half the time, a moving object is not being recorded by the film camera. And motion is sampled 24 times a second.

An classic interlaced scan camera shoots either 50 (PAL) or 60 (NTSC) fields per second, and there are two fields for each frame of video, hence why PAL is 25 fps and NTSC is 30 fps. But the interlaced-scan cameras are capturing reality as a series of fields, not whole frames (a field contains every other line needed to build up a whole frame; the second field contains the alternate lines.) So a moving object is in one position on Field One and moved to another position on Field Two. A video camera has an electronic shutter, but it is common to shoot without the shutter on, so at 60 fields per second for NTSC, the exposure time per field is 1/60th of a second.

So imagine the difference in motion rendition from a camera that takes a whole frame 24 times a second with a shutter closed 50% of the time, versus a video camera that takes a field 60 times a second, with no shutter usually employed, so no temporal gaps between each image taken, and with the second field being interlaced with the first to create a whole frame of video.

Since 60 times is a higher sampling rate than 24 times, motion tends to look more fluid and smooth with standard 60i video than with 24 fps film. This would not be true if a film camera was running at 60 fps and the image was then projected at 60 fps.

So motion rendition is one of the classic differences between 24 fps film and interlaced-scan video. This is why there has been an interest in 24P video cameras, which capture reality 24 times per second as entire frames (progressive-scan instead of interlaced-scan.)

Besides motion rendition, other comparison issues are resolution, exposure latitude, grain vs. noise, random grain structure vs. fixed pixel grid pattern and how that affects aliasing and edge detail, artificial sharpening used by lower resolution video cameras, gamma curves (how they handle extreme under and overexposure), video artifacts like compression, color-subsampling, pulldown issues when converting 24 frames to 60 fields, interlaced-scan artifacts when deinterlacing, and how all of these interact with the method of presentation (35mm print projection, digital projection, HD, PAL, NTSC broadcasting, etc.)

To go through all of that would take several posts. I'd start doing some Google searches if I were you, and get some textbooks...

 

[Lazlo]

On the specific side, how does shutter angle affect the picture? I never understood why a cinematographer would choose one shutter angle over another, and how??? I mean, the shutter gets out of the way of the film for 1/24 of a second or whatever to expose that frame, closes, then opens to expose the next frame. Why doesn't this feature exist for still 35mm cameras to achieve whatever affect it achieves? Thanks.

 

[Stevie]

That was very helpfull, thanks. One more, do you know any stats of whom uses digital and whom uses film in the endustry? Thanks.

-Stephen
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AsiansXX

 

[David Mullen ASC]

I don't have any stats, only what I can see from where I'm standing (and working). A majority of sitcoms have switched from 35mm to 24P HD, but only a small percentage of narrative (fictional) shows and commercials that traditionally use film. I can only think of a few (Enterprise, Joan of Arcadia, Huff, American Family...) A lot of under 1-mil indie features have been shot digitally in all sorts of formats (HD, DV, etc.) and as the budgets get even tinier, you see a lot more DV being used out of necessity. I've been shooting a lot of HD features lately in the half-mil to 3-mil budget ranges. But in the over 3-mil budget range, not that many people are shooting digitally still. You have exceptions like "Collateral" or "Attack of the Clones" or Robert Rodriquez' "Spy Kids" sequels, etc.

A film camera usually uses a 180 degree shutter, so at 24 fps, the typical shutter SPEED is 1/48th of a second. It's physically impossible to shoot at 1/24th of a second at 24 fps and get a usuable image because the shutter has to be closed part of the time to allow the film to advance to the next frame -- the film only moves through the camera BETWEEN exposures; it's rock-steady when the shot is taken.

A still camera can be set to a similar shutter speed, like 1/60th or 1/30th.

You can only shoot long exposure times in a movie camera by lowering the frame rate. For example, if you drop down to 12 fps with a 180 degree shutter, the shutter speed is 1/24th of a second.

You can shoot at normal frame rates but shorten the exposure time by closing down the shutter angle. For example, at 90 degrees at 24 fps, your shutter speed is half of 1/48th, or 1/96th. At 45 degrees, it becomes 1/192. The motion gets very choppy and jerky looking, ala the "Saving Private Ryan" battle scenes.