During one full cycle of shutter, is open phase first followed by closed?

[MikeHi]

Technically speaking, when describing one full cycle of a shutter, is the open phase first followed by closed phase, or the other way around?

If it makes any difference, my question refers to the movie cameras (high end amateur cameras) from the mid 1960's. But I believe the basics of shutter did not change since then

Specifically, if a camera has speed of 18 frames/sec, and shutter speed 1/40th of a second, then in each frame the shutter is initially open for 25 milliseconds and then closed for 30 milliseconds, and the cycle repeats. Is it correct?

 

[BrianV]

That sounds reasonable, Silent Super-8 movie cameras were 18FPS, and they used a rotating shutter with a "cutout" in it. Regular-8 Silent cameras were 16FPS.

The Kodak XL series, and later used a larger cutout and a slower shutter speed, more like 1/30th.

Somewhere in a pile of old Pop and Modern Photo magazines I have an article that explains the difference between the Kodak XL cameras. Included was a diagram of the shutter mechanism showing the increased slit size.

Sound cameras often run at 24FPS for better sound fidelity.

What camera are you using?

 

[Helen B]

All the movie cameras I have used had the shutter closed when in the stopped position, if they were working properly, therefore you could say that the cycle begins closed and ends closed. A few may stop with the shutter open, but by and large the better ones would be designed to stop with the shutter closed. This applies to both electric and clockwork cameras - even when the clockwork winds down (a decent clockwork camera will cut out before the speed drops too much from the set point, some cheaper ones allow a slow-down). Some shutters are oscillating, notably many Bolex and Beaulieu, and the Eclair ACL, while others are rotating. Rotating shutters lead to the use of shutter angle - ie the proportion of the full rotation that the shutter was open for. 180° means that the shutter is open for exactly half the full cycle, and is common. For example at 180° and 24 fps, the shutter would be closed for 1/48 s and open for 1/48 s. Angles can vary by camera, and some cameras allow the shutter angle to be varied from the maximum to almost (or even fully) closed. That adjustment may have had to be done while the camera was not running, depending on the camera.

While 180° is probably the most common default/maximum angle for a camera, the maximum angle could vary from around 170° to over 220° for some cameras. Cameras with oscillating shutters often used the nominal shutter angle, simply because it was the normal way of describing shutter speed. Your example would be a 162° shutter.

The Bolex reflex cameras with a beam splitter (and zoom lenses with a beam splitter and viewfinder built in to the lens itself) instead of a mirror in the reflex viewing system used a shutter speed fiddle to account for the light loss - ie they used a true shutter speed, and a corrected one for exposure equivalence. You would need to know which one was being referred to if you wanted to know how long the shutter was open for.

Projectors are entirely different, by the way. They usually have shutters with two or three blades, so that the flicker cycle happens at around 50 Hz or higher. A two-bladed shutter on a 24 fps sound projector results in a 48 Hz flicker. A three-bladed shutter on a 16 fps silent projector also results in a 48 Hz flicker. There's an old joke about a guy who asks for half his money back after watching a movie, because he sat in the dark for half of the time. The ticket seller refuses, because he points out that he saw the movie twice.

 

[MikeHi]

That sounds reasonable, Silent Super-8 movie cameras were 18FPS, and they used a rotating shutter with a "cutout" in it. Regular-8 Silent cameras were 16FPS.

The Kodak XL series, and later used a larger cutout and a slower shutter speed, more like 1/30th.

Somewhere in a pile of old Pop and Modern Photo magazines I have an article that explains the difference between the Kodak XL cameras. Included was a diagram of the shutter mechanism showing the increased slit size.

Sound cameras often run at 24FPS for better sound fidelity.

What camera are you using?

This is about Zapruder camera
Zapruder Camera

My question is not about whether the settings make sense. It is about their interpretation. I assume that it would not make sense to start a frame with shutter closed. This means the open phase has to be first, followed by closed phase

Does it mean that my assumption about the order is correct? The first phase is shutter open for 25 milliseconds and then closed for 30 milliseconds, assuming 18 frames/sec and 1/40 shutter speed

 

[Helen B]

In the camera's terms the cycle begins and ends with the shutter closed. If you are considering the film itself, then it depends whether you begin at a frame or at a frame line - the frame line being beside the sprocket hole on 8 mm and 16 mm film. The frame is taken with the film stationary, of course (except in a high speed camera, which this isn't), then the frame advances quickly during the shutter blanking period. It would help to know more about the context of the question.

If you referred to 'frame 1', 'frame 2' etc, then you could say that the cycle begins with the shutter open for the first frame. If we assume that your 25 ms - 30 ms timing is right, then frame 1 represents 0 ms to 25 ms, frame 2 represents 55 ms to 80 ms and so on. There is no other frame of reference to tell us where to set zero time.

However, cameras rarely come up to speed immediately, so the first frame or two may have lasted longer, if they begin with the camera stopped. If they are clipped from a sequence with the camera already running then there would be no speed up. You should be able to tell by an analysis of the exposure, but that isn't very accurate. You need to be realistic about these timings. I understand that the average speed was determined to be 18.3 fps, and the frame-by-frame variation was between 18.0 and 18.5 (from the later FBI tests of the camera). The shutter angle for that camera appears to have been between 165° and 170°. The shutter speed would, of course, vary in direct proportion to the frame rate.

PS The more context and info you give us up front, the less time we waste giving you irrelevant information in an attempt to cover all possibilities.