Ramping
ways to change camera speed & hold exposure

by Rick Wise /director of photography
and assistant cameramen: John Chater, Joe Ward, Rod Williams, 

Seductive, beguiling, the sedan zips around a mountain corner, instantly slows to a crawl, then dashes around the next curve.  No cuts.  

How do they do it?  Ramping.  The speed of the camera -- or the apparent speed -- changes from slow to fast and back to slow.   Of course, when you slow the camera's speed down then screen action speeds up.  Speed up the camera's speed, and screen action slows down.  

Most probably this ramping was done in post.  There are significant advantages to changing apparent camera speed after  the shoot.  Those advantages center on cost and perfection.  A good argument can be made, however, to make the changes in-camera.  See the side-bar by Rod Williams below.

If you are going make the changes in-camera, there are two different ways to go at it:  one method changes iris in the lens in "perfect" sync

with camera-speed changes -- speed up the camera (which slows down the screen action) and the system opens the iris; slow down the camera (which speeds up the screen action) and and it stops down the iris.  The other system changes the shutter angle:  speed up the camera, and this system opens the shutter; slow down the camera, and it closes down the shutter.  Both try to keep exposure constant. At the bottom of the page is a list of cameras you can use for each technique.

Rule #1

Fix it in post.  If you can.  Why? Because the in-camera systems can cause or be problems: 

  • The add-on system to alter either iris/camera-speed or shutter/camera-speed takes time to install, then time to program and rehearse.  So you incur significant costs in crew/set time.

  • Iris-based systems are prone to backlash or lag.  If you change the camera's speed too quickly, the iris will either lag as you start or over-compensate as you stop.  As a result, the image will briefly be over or under-exposed.  Rule of thumb: if ramping in-camera, do not change faster than 2 stops/second.

  • Some cameras may have a shutter wobble that shows up as a flicker if you ramp down then up and the shutter is set at less than 180 degrees.

  • Shutter-based systems can create screen flicker during speed changes.  This seems to be due to the fact that when you close down the shutter (which you would do as you slow the camera to make the screen action go faster) you make the image sharper -- and at slow speeds this extra sharpness causes strobing.  Were you shooting at 3 frames/second with a normal shutter,  any fast movement of either camera or subject causes a natural blur on each frame, which on the screen makes the images seem continuous and smooth.

  • Your changes will be approximate.  No matter how perfect your Assistant Cameraperson is, he/she is estimating what   the director or you want.  

 

Do It In Camera

by Rod Williams

When I've been on shoots where we've used the 435 for ramping, it's been to get the vision of the director of DP on film rather than leave it to the agency or client in the editing room.  It's also been usually in situations where they had a pretty clear idea of what they wanted on film. 

With the 435 it's so very easy to speed ramp and very easy to change the time, angle, etc., as well as program the ramp time and the screen time.  

I've done lots of car stuff like that.  It's obviously a little trickier with an iris control unit and I don't generally think that is a good idea unless there is a really compelling reason to do it in the field.

One reason would be like a shoot I did recently where we shot a number of scenes where we would shoot most of a long take (on the street following a number of people) at 6 or 12 fps then ramp to 24 or 36 for a bit then ramp down to 6 or 12 for more slow schmere.

Shooting it all at the 24 or 36 fps would eat up way too much film and I don't think the look is quite the same with with a post effect as committing it to film.

This is not even getting into the whole issue of post driven production where the post effects people continue to diminish the contribution of the DP and others in production.

Soon we will not be engaged in cinematography, but rather in data acquisition and the post people will make the important creative image decisions.  Don't laugh.  I recently worked on a four-day commercial with lots of effects.  If it were up to the CG post people we would shoot everything with flat, shadowless lighting in super 35 with slightly wider lenses than needed and they would do all the lighting effects and composition in post.  Snarl!!!

 

     

  • On the other hand, in post, the director / producer / client can make an exact decision about where the change happens, for how long,  how big a change, and where the scene changes speed again.  (Of course, as the DP, you now no longer have a say....)

  • Iris-changing systems cost approximately $370/day and usually with a three-day minimum.  Shutter systems are much less expensive but only work with some MOS cameras.  (See below) 

  • If you ramp in-camera and are using HMI's, then you must shoot with square-ballast/flicker-free units, which cost considerably more than regular ballasts.  (However, if you want to shoot at 48 frames, you will still need square-wave ballasts since at 60HZ 48-frames is not a flicker-free speed.  A possible work-around is to set the shutter at 144.)  See Flicker-Free table.

  • In post, Flame and other post computer-systems can add blur to your shots to make them look more natural when they appear to be running at 3 frames/second.

Solution:  shoot at the highest speed you will need in the shot, then adjust slower speeds in post.  If your highest camera speed would be around 48 frames/second, then shoot the entire scene at 48 frames.  Flame and other post systems will let the editor speed up the action by dropping frames and also add a natural blur.  

But: Rule #2

Sometimes you need to ramp in-camera: 

  • Addendum
    by Joe Ward

    The real secret to effective ramping would be knowing the parameters of the time needed and the camera's capabilities.  If you are within each of these windows you should get the results you desire.  Sometimes when some DP's use the ramp effect, they are experimenting to get a weird effect of over-exposure.   I am beginning to believe, along with you, that most effects can be achieved in post.

     

    • If you need part of the scene to be in sync sound, and if shooting the entire scene at 24 or 30 frames/second still won't allow you to create a smooth slow-motion segment,  then in-camera ramping is the ultimate tool.  Just work within the limits -- "instant" apparent camera-speed changes cannot happen.  Keep the change under 2 stops/second.

  • You don't have access to an effective post process to speed-up / slow-down / smooth out the screen action.

 

And: Rule #3

Test it.  As the DP, you "own" the camera performance for your job, your situation, your techniques.  Whenever possible, try to test out ramping or any other technique new to you before the "real" shoot.

Here are links to further discussion on ramping:

Cameras which must use an iris system to ramp in-camera:

35mm:

  • Arri 535 B

  • 435 NOT ES (electronic shutter -- most rental units have the electronic-shutter version)

  • BL lll

  • BL lV

  • ll C

  • Moviecam SL

  • Moviecam Compact

16mm:

  • Aaton -- all models

  • Arri SR ll

Cameras which can also use a shutter system:

35mm:

  • Arri 35 A

  • Arri 435 ES

  • Panavision Millenium

  • Panavision Gold and Platinum:  in theory capable of shutter changes via the "Smart Shutter Control.  "My experience was that it wasn't smart, it was a liability.  It could turn a 10-hour day into a 14-hour day with no guarantee of getting the effect, and probably guaranteeing the unfortunate A/C the next day off!  Backwards engineering at its worst." -- John Chater