vary aperture through shoot

Discussion in 'Digital Video' started by arjen92, Oct 19, 2012.

  1. arjen92 macrumors 65816


    Sep 9, 2008
    Below sea level

    I wast thinking about how you can change the focus from one subject to another. Then I thought to myself, what if you can change the aperture while filming. A scene could by like this;

    A guy is thinking to himself, he is in focus, the background is blurred, then he thinks about the people around him, the aperture is closed and the background gets in focus. Since it's about him and the people around him, getting them both in focus shouldn't be that weird.

    I realize that the brightness would change. But technology should be able to work around that.

    So, just wondering what your thoughts are on this. I would especially be interested if there's already someone doing this (so a link to an article or video).


  2. dasikes macrumors 6502a


    Jul 10, 2008
    You would be much better off doing an effect like this in post production. To accomplish what you are talking about in camera would change exposure far too much to go unnoticed. You'd basically be going from the fastest to slowest aperture value of a lens.

    If you really want to try this, look for tutorials about faking focus blur in After Effects, Motion, FCP or whatever software you use.

    Hope this helps.
  3. Policar macrumors 6502a

    Nov 21, 2004
    I was in the process of trying this five or six years ago with a fast 50mm and an aperture pull time up against a fader ND pull...didn't pan out. I think this would be very hard to do well for a lot of reasons.

    The Wachowskis do this (in post) in Speed Racer, for a similar effect to what you tried. Say what you will about that movie, the Wachowskis' handle on shot syntax is exceptional, and so if you thought of what they thought're in good company at least. But they did it in post (and they also used heart-shaped bokeh, etc.--cute).

    If you shot on Alexa or the red with its weird HDR mode you could get the DR necessary to do this in a low DR scene even without the fader ND, no problem. But you'd have to do some impressive post work to maintain the exposure. But it's possible, absolutely.
  4. daybreak macrumors 6502a

    Sep 4, 2009
    In the 60s we did what you described on film called pulling focus. It is easy done but you need a camera which lets you do manually focus instead of auto.
    Manually put your actor in focus and then slowly pull him out until the background is in focus.:rolleyes:
  5. Policar macrumors 6502a

    Nov 21, 2004
    He's not referring to pulling focus, but rather to pulling aperture at the same time as the lights (or NDs, or shutter speed) change in intensity, so that the exposure remains consistent as the aperture (and therefore depth of field) changes.

    Before giving such a sarcastic remark, read the actual post.
  6. TomCat macrumors member

    Jul 12, 2000
    Well, I think any sarcasm there was imaginary.

    I think its a worthy goal, but most of that can be duplicated (a little more dramatically) by the old Alfred Hitchcock technique of dollying in while zooming out, which changes the depth of field without a change to the aperture. The main subject stays essentially still; the foreground and background change focus and move a little bit. Not quite the same thing, but in most cases probably even better.

    Hope that wasn't too sarcastic for you. :p
  7. Policar macrumors 6502a

    Nov 21, 2004
    I agree the Vertigo zoom is a great (if overused) technique, particularly in Jaws and Poltergeist, but it communicates something slightly different (change in the scope and focus of thought but maintaining a focus on the real world rather than a change from thinking internally to externally). In some cases, could be close enough.

    I think it's worth doing this..but probably just doing it in post. A follow focus geared to both an ND fader and aperture would be the easiest way. Timing an aperture pull to pull on a fader/variac would work except for the color shift.
  8. nateo200 macrumors 68030


    Feb 4, 2009
    Northern District NY
    I'd test this prior to actually doing this. I've actually tried this and its a pain in the you know what trying to match the exposure changes....Just make sure you protect your highlights and keep your shadows so they are not too muddy because with a DSLR (I'm assuming your using one) the 8-bit 4:2:0 is a very unforgiving format change something say by a stop vs real 4:2:2 from an Alexa or whatever....I know how to do this in post edit much easier though...essentially you would shoot with ultra deep focus at say like f/16 to f/22 then use a plugin to use artificial bokeh around the subject in focus and then slowly fade it out or whatever....I'm totally drawing a blank on the name of the plugin though.

    You could alternatively just do a good "old fashion" focus pull as someone sarcastically remarked, not sure why as I regard focus pulling as vital and when I have the ability to run 2 monitors (one for my self and one for another) have a dedicated focus puller and practicing where to pull the focus before shooting is a way to make your short film look like a real ace shot it. But again just practice this stuff before you do know what is the worst? trying to salvage a ruined shot in post edit after the opportunity to re-shoot has passed... :mad: you'll be sitting in front of a computer for hours only to get a semi decent result.
  9. arjen92, Oct 20, 2012
    Last edited: Oct 20, 2012

    arjen92 thread starter macrumors 65816


    Sep 9, 2008
    Below sea level
    Thanks for the replies!

    I was watching Madagascar 3 where there's one shot in which the zebra shoots through the air with the seal. The camera focuses on the two of them and the balloons (or bubbles) get all blurry, a really shallow depth of field. Then the zebra falls down again, the camera keeps focus on him, and the balloon are crystal clear again.

    It didn't feel like how normal lens would act (having both a very strong bokeh, but also a deep field of depth), so that's what triggered my attention and made me think. Of course Madagascar is digital, so I understand that they could've composited stuff. But if I'm not mistaken a lot of stuff is done with a digital version of a camera and lens, not just "a camera".

    So thanks for the tips, but I won't be shooting this myself. I was just wondering whether a director did this in real life. Cool to read some of you guys tried (with the ND filter etc). I didn't think it would be that weird for a director to do, since Peter Jackson made all these mechanics for a forced perspective with a moving camera..

    So they did something like that in Speed Racer? Cool to know, never saw the movie. I think I'll go watch it soon.

    Still curious if there's a director that doesn't like to fake it and actually does it in real life. Perhaps it's not worth the energy. A dolly zoom is of course much more dramatic.


    Well, the reason I'm asking is because pulling a normal focus has been done since the 60s. I've been watching movies more closely lately and a lot of dialogue shots are done like that. Therefore I was intrigued whether there would be a different way of filming dialogue that's less standard and doesn't force me to look at one actor who is in focus.

    p.s. I'm not going to shoot. Just some thoughts I'd like to share.
  10. juanm macrumors 65832


    May 1, 2006
    Fury 161
    On high end cameras like the Arri 435 you could do that. Change the fps while shooting, and compensating the iris or shutter <

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