How do I setup a speed ramping shot?

A few cameras, including Konvas and Kinor cameras with certain additional motors, and the Temp SKL, are rampable.

This means that the camera can smoothly change speeds while in the middle of a shot. This can be a nice addition to a scene, since you can show the subject running past the camera at normal speeds. Then, when the subject gets to a certain position (usualy directly in front of the camera), the shot is slowed down to the point where the viewer can see the emotion, sweat, or tears. While some movies seem to take this change in speeds to excess, this can still make for a very nice addition to a shot.

So if a camera can speed up/slow down its frame rate, then the question remains of how to properly setup for shooting a ramping shot.

On September 19th, 2007, H.W. Stone had this to say in response to a question concerning the proper procedure for a shot that ramps the speed:


The easiest way to handle a ramp is to change the lighting-- pull a lockjaw scrim outward as the speed goes up OR use a double polarizer and dial it to match exposure. In reality, most ramps don't really need a change in exposure, but if you were to go from 24 to 128fps you would want to keep the same f-stop for DOF, so changing ND (meter the double polarizer off the camera to get the values) or pulling a lockjaw makes more sense.


konvas with rheostat motor

Richard Garbutt had this to add:

Changing aperture messes with depth of field, so coupling the variable shutter to the motor speed is generally preferred. Though I can think of dramatic uses for shifting depth of field within a shot.


As well as this:

Two other solutions suggest themselves to the problem, and their application again falls into the "it depends" bin. It's always a question of using the right tool for the right job at hand right this moment.

Solution #1: Vary the intensity of the set lighting as the camera motor speed changes. Probably for the most part impractical, as slaving these together ain't gonna be easy; tungsten light sources change color temp as they're dimmed, and it's nigh impossible to affect outdoor lighting (including seeing outside via windows and doors). BUT for certain, highly-controlled interiors, this might be an option, or at least, a possibility. Always be aware of possibilities, as
sometimes they can bail your sorry butt out of a nasty bind.

Solution #2: At some telecine houses (including mine, which is Studio Post & Transfer in Edmonton, AB), it is possible to ramp in an exposure compensation during transfer. Considering the latitude of modern films, this is probably practical for a ramp of up to 2 (maybe more, which would cover your TEMP
[SKL] question) stops, which would cover a ramp from, say, 24fps to 96fps. There may be issues with shifts in contrast/graininess, but it'd be one heckuva lot simpler than designing a unit that will slave your variable shutter to the motor. Cheaper, too. Expedience, that's the ticket! If you're thinking of doing this, I'd suggest aiming for a (say) 1-stop "over" exposure at the heaviest exposure end of the shot; splitting the difference, if you will. This will leave you with at least reasonable exposure at the light exposure end of the shot, and help prevent your blacks from getting noisy. Tests before production footage are always a fabulous idea.


Todd Terry also added:

Exposure certainly changes with speed ramping. I remember hearing some commentary from Roger Deakins when he shot "The Man Who Wasn't There," which contained a few speed ramps. I remember him saying there was some camera system in place which adjusted exposure as the speed ramp went up or down. I can't say whether that was adjusted via shutter or iris changes, Deakins probably didn't specify at the time.

Even without iris adjustment, since negative film has such a wide latitude if the exposure was very good I'm betting a good colorist could take care of that very well, as long as the ramping is not TOO severe.

Ramping without exposure correction could be pretty cool if that was a desired effect... as you ramped toward slow-mo, the picture would darken, obviously,.... and conversely if you ramp toward higher speed, then the picture would eventually burn to white. Might be neat.