Thursday, November 14, 2013

SHUTTER CONTROL AND F/STOPS

Can I Cut The Light With The Shutter Setting?

Bolex D8L shutter settings varies from about 180 degrees (the silver half-moon) to zero degrees (the black half-moon). The half way setting of  90 degrees is accurate enough. So the answer is yes, you can a light cut 1 stop by selecting the mid point shutter setting. Controlling the light with the shutter does works well in still photography as the images are not moving.

If you set the shutter to half-closed (the half black/half silver HALF MOON symbol on the shutter dial), that setting is half way from the maximum open of 180 degrees to fully closed. About  90 degrees. The shutter angle will be cut by 1 stop. See page 47 of the Bolex D8L manual.

See this link for more of how a shutter works:


D8L accuracy is not specified, but it should be in "ballpark acceptable". As with all footage shot on a Bolex, keeping records of the setting and the results is a very good idea. Everybody's mileage will vary as the camera settings/projectors/screen combinations will always be different.

Movie Film Camera
Use and effect of the shutter is slightly different with a movie film camera.  There are 3 basic ways to set light with a motion picture camera:

          1) Set the iris for the light - The DOF will be what
          it will be. This is how the Bolex manual explains
          setting the iris for the light.

          2) Set the pre-selected DOF with the iris, and
          control the light with ND filters or more light.

          3) Use both ND filter and iris settings in
          combination.

The method of setting light in professional motion picture film production cameras is primarily through a pre-determined iris setting (f-stop) and then re-adjusted for actual light using neutral density (ND) filters. Typically you will have either too much light or not enough.

With too much light, you can close the iris slightly or add an ND filter. Too little light, open the iris or take out or decrease the ND filter's strength. The situation here is changing the iris will affect the depth of field (DOF). ND filters will not affect the DOF.

How To Set
First, you select the location (indoors or outdoors) and the subject. Say you desire an f~5.6 setting for a slightly blurred background. Using your lightmeter, get the approximate f-stop setting by metering the subject after dialing in the f-stop for f~5.6 on the light meter's dial. Next, add or subtract light, as necessary using ND filter, bounce cards, light fixture, etc, to get the correct amount of light.

More Or Less Light
Outdoor light can be raised with a bounce card, an auxiliary hot light, etc. Outdoor light can be cut with an ND filter and anything that will lessen the light falling on the subject. Indoor lighting can be adjusted with bulb changes, additional lamp fixtures, scrims, etc, or ND filters. Obviously this is more work than just turning the iris to f-8 to chop 1 stop of light.

Effect of Short Shutter Angle On The Look Of The Film
If you use the shutter control to chop that one stop of light, the resultant moving picture image(s) will also be changed. The shutter's angle is now at a shorter angle of 45 degrees and can now impart a "stuttering appearance" onto the film depending on other settings. See "Saving Private Ryan", or The Gladiator", for examples of short (45 degree) shutter angles.

Also keep in mind that shorter angles will affect panning rates. Anytime a panning rate exceeds a particular speed/shutter angle/FPS settings, a corresponding condition will be created called "Rolling Shutter". Also known as "The Jello Effect" because of the look of the effect on the finished film. The rolling shutter/jello effect has been with filmmaking since the 1st film camera was invented. Is due to too fast of a pan rate and is 100% operator controllable. Got rolling shutter? Pan slower.

More here:


ND filters or gels can also be used over windows to control light. Windowed gels can be used in conjunction with other lens filters to allow sunlight to be shot with indoor film. Or you can gel the indoor lights to match the outdoor light color temperatures coming through windows. With a film camera there is no white balance to correct for off-white conditions, but you can have the film converted to digital format and balance the digital footage if the color is slightly off.

Here's a link with some more info:



And finally, there is a somewhat rude, but technically correct answer, as to the effects of small shutter angles in a motion picture camera:



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