Should shutter speed always be double?

[Daniel Weber]

Originally Posted by Tim Gray

>>Also is it true that shooting at a higher shutter speed
>creates more shallow depth of fields?

No.

Well, if you shoot with a higher shutter speed it will lessen the amount of light coming in and thus you would have to open the lens more, which will drop your depth of field.

Tim is technically right, but a higher shutter speed will allow you to shoot more wide open to drop you DOF. You can also achieve this with ND filters. There a multitude of things that can control your DOF. In still photography shutter speed is a more common way of controlling DOF, not so much in video.

Dan Weber

[Tim Gray]

Sorry, I should have been more clear. Shutter speed in and of it's self doesn't affect DOF. Aperture, focal length of lens, and distance to subject affect DOF. Other variables that make you change those three quantities do have an indirect effect on DOF, but only because you are changing those quantities.

I would think using ND filters is a better way to go about it unless you specifically want the high shutter speed look.

If you really want a crash course on getting enough light for an exposure, get a digital camera with real macro lens and take some close ups of bugs. You need a quick shutter speed to freeze the motion. You need a small aperture to make sure even a fraction of the damn thing is in focus. This makes for a really dark picture - so get a flash.

At least that's how I think about it. Aperture affects DOF, shutter affects motion, and the two combined affect exposure on film, depending on the light.

[Robert Jackson]

Originally Posted by Tim Gray

You get more motion blur the longer the shutter. The 180 degree shutter (1/48th for 24 fps) is traditional from film.

http://en.wikipedia.org/wiki/Shutter_angle

That's one of the better explanations I've seen on the web. I usually have to pull out a camera body and let someone see the shutter before I can explain it clearly.

A variable shutter can really yield some interesting effects. It used to be that people would rent an Arriflex for music videos and very little else, but now those kinds of looks have become a lot more widely accepted. Of course, Saving Private Ryan is the big one that's even referenced in that article.

I think seeing the kinds of stuff people are shooting with variable shutter speeds on video has had a pretty big effect on what's considered aesthetically pleasing. It's like Toland using 24mm lenses on Citizen Kane. It was considered "freakish" at the time, but now 24mm isn't even really a very wide angle for most DPs.

[Tom Hardwick]

24 mm doesn't even look especially wide on full frame 35 mm, let alone the half-frame as used in the cinema.

[Kevin Shaw]

Originally Posted by Tom Hardwick

I'm one of the few that seem to much prefer this silky, creamy motion smoothness, coming as it does with 50 different (half resolution) pictures per second.

Don't worry Tom, you're not alone. I can't think of a single example where I liked a movie or TV show better because it was shot at a low frame rate, but I'm frequently aggravated by the "motion judder" caused when video cameras are run in progressive-scan mode. I see this regularly on TV news now, and it's most noticeable any time there's a scene with fountains or other running water. The same was true for sample footage from the HD100U being shown by JVC at the WEVA Expo last August, which didn't help my impression of this camera.

I see no logical reason to propose shooting video at 24p and would rather see us move toward 60p, but I'll settle for 60i for now. As I've said before, life doesn't happen in 24 incremental movements per second, it happens continuously.

By the way, regarding people setting their HDTVs to "stretch" mode to fill their screen with 4x3 footage, that's why we should all start thinking about offering widescreen output for paid video projects. I can't stand watching 4x3 footage on an HDTV with "pillarboxing" on the sides of the screen, so darn tootin' I've got my display set to fill the screen. I look forward to the day when most content is widescreen format, and preferably in HD to boot -- at 60 fields or frames per second, thanks.

[Robert Jackson]

Originally Posted by Kevin Shaw

I see no logical reason to propose shooting video at 24p and would rather see us move toward 60p, but I'll settle for 60i for now. As I've said before, life doesn't happen in 24 incremental movements per second, it happens continuously.

Exactly the point. Was it Truffaut who said that cinema is a lie that unfolds at 24 fps? The unreality of 24 fps is exactly what's attractive about it. I remember Douglas Trumbull debuting Showscan for a bunch of production people some years back and thinking they were all going to be blown away by film running at 60 fps and got exactly the opposite reaction from most of them.

As far as motion judder goes, the formulas for pan speeds are right there in the ASC handbook. All it tells me when I see people shooting HD poorly is that they shoot HD poorly. ;-)

-Rob

[William Hohauser]

Originally Posted by Tim Dashwood

Actually, it was interlacing that was born out of necessity.
24fps on film was established as the threshold at which humans percieve motion (originally it was 18fps) so the logical conclusion was to photograph and project 24 fps.

The first TV systems, using the same logic, were actually progressive scan, but because the refresh rates weren't high enough, there was a phenomenon during panning called "ripping." It meant that objects would appear to skew as the camera panned. For example, a flag pole would suddenly appear to be on a 45° angle while the camera was panning and then become upright in the static shot.
The engineers' solution was to split the workload and do two half scans - which became known as interlacing.
60Hz was chosen in North America because that was the frequency of AC power (which was originally used to clock the cycles) and 50Hz was chosen for Europe for the same reason.

As I was told (in broadcast licensing class), interlacing was a way to reduce the bandwidth of the broadcast signal so more channels could be fit into the allotted broadcast spectrum for television signals. By reducing the size of the frame to two alternate fields of 260+ lines for a total frame of 525 (including sync signals) and taking advantage of the amount of time the television set phosphors remain activated, they were able to achieve 30 frames per second in roughly half the bandwidth. A sort of analog compression. This technique requires that the cameras take images at 60 fields a second. I assume the shutter is at the same rate or slightly higher.

The pan skew was a result of slow scan rates. Probably slower then 30 fps. Very old press cameras used to do that also. Race photography sometimes had that effect in the 1920's. Animated films would imitate the effect since the skew gave an exaggerated sense of speed.