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last modification: february 10th, 2012

Truth and myth about variable shutter and wide shutter angles

Standard shutter:  see this view from cartridge compartment frontwall with shutter and filmgate of a camera. The 180° shutter is rotating between lens and filmgate. In this case half of the time for one turn (1/2 of 360°=180°) the shutter lets pass the light to your film. The other half of time the filmgate is covered and this time is used to transport the film to next pictureframe. In the time of exposure the film “stands still” behind the filmgate to allow sharp pictures.  Depending on framespeed fps (frame per second) the shutter is normally rotating 18  or 24 times in one second. Different camera mechanics of the shutter can be more closed or more open. (The time for moving the film to next frame is than shorter or longer). Most cameras have shutters up to 160° (shorter filmspeeds). Intermediates up to 190° and lowlight cameras have up to 230°. The opening time of the shutter has influence of the amount of light which can pass onto the film for one picture. This time is measured in “shutter speed”.

This is important if you want to take scenes at evening, dark wintertime or other lowlight conditions. Fade functions are realized by closing or opening the aperture.

sample from AGFA movexom 6 mos electronic

Conclusion:  large shutter openings have longer shutter speeds! This is good for lowlight conditions, but not so good if you want clear, sharp pictures of moving objects!

resulting shutter speeds depending on shutter opening angle:

shutter

 for 18 fps

for 24 fps

 for 36 fps

225°

1/29

1/38

1/58

220°

1/30

1/39

1/59

200°

1/32

1/43

1/65

180°

1/36

1/48

1/72

160°

1/41

1/54

1/81

140°

1/46

1/62

1/93

120°

1/54

1/72

1/108

100°

1/65

1/86

1/130

80°

1/81

1/108

1/162

60°

1/108

1/144

1/216

40°

1/162

1/216

1/324

You know what it means if you choose speeds below 1/40 second! It is hard to get real sharp pictures while shooting out from your hand.You need a tripod.

.. and what´s about moving objects?

The variable shutter allows to modify the opening angle, so this camera is a little bit more universal and you can use the same camera for different solutions. You can choose a more closed shutter (short shutter speeds) to keep moving objects sharp.This can be fixed normally in one or two steps which results in one ore two different shutterspeeds. Variable shutterclosing or opening  between 0 - max. degree. is used for fade functions.

  Not more! You can see at the table above: you have allways keep in mind what you actual do!

Variable shutters can range normally from 0° to 170° (Nizo 480 up to Nizo “professional” range from 0-150° and has one step at 75°. This results in two shutterspeds for filming of 1/86 and 1/43 sec.  Other cameras have other shutteropenings and differs ( see table), 

  • variable shutters have their advantage in more sharpness of objects during movement (due to possible shorter shutter speeds)  -
  • but also a disadvantage in lowlight conditions. You had to use other film with higher filmspeed or artificial light.

You see: for lowlight conditions with normal 18 or 24 fps  special cameras are much more usable. This is the domain of cameras with standard shutters e.g. BOSCH/ BAUER or some other cameras with shutter openings from 200° up to 230° and gives you 20%- 25% more light than a NIZO 800, 801 or PROFESSIONAL !) plus lowlight lenses (1.2 or 1.4). An exception are Canon 814 and 1014 which are constructed with a variable shutter with two positions of 150° plus XL shutter 220°.. Using a solid tripod, cable release or remote control with lowlight cameras is s “must” to avoid soft pictureframes.

The intermediate standard shutter (170 - 190°) is a good choice and recommended for standard usage.

A camera with 150° or  160°  standard shutter (~ 1/43 sec) is a good choice if you want to get sharp pictures and avoid the risk of soft pictureframes. Here you can get for less cameras with good lenses (except rare collection items).

But keep in mind:  scenes in 18 or 24 fps with fast movements are never clear and sharp. even if you have shutter speeds of a variable shutter! Maybe the Beaulieu 4008 with its “highspeed” variable shutter (1/65 -1/130sec.) and a Fujca (1/41 up to 1/161 sec) is a good choice....

Clearance of myth, regarding the fade function of cameras: Movie cams with variable shutters can close totally, so you can fade from dark to normal light and reverse without changing aperture opening.  Fade function of very few simple cameras with standard (no variable) shutter can close down only to the smallest aperture opening (f/stop = 22 or 32) This is not a real problem while two pictures are overlayed.  Most Super 8 cameras with standard shutters can close diaphragm for fade functions totally to dark and reverse (excamples are the AGFA MOVEZOOM 10 / 6 mos electronic, the  BOSCH / Bauer “C” or” S” series (Porst), some Cosina and others)

All automated fade functions (variable shutter or  aperture) shows the same results: from bright to dark and back to bright.
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