Exposure and FPS change ON SHOT.

[bhangima]

Friends,

Quite often we see some shots in movies where different exposures and different FPS rates are used within the same shot. I know that part of it can be done during the POST, but I would like to know if anyone has experience in shooting where FPS and exposure change was required ON SHOT.

Assuming you are the director, how would you communicate to the Cinematographer on the exact timing at which the change (in FPS and Exposure values) to take place? Also, if you are the Cinematographer, how would you plan for such shot?

I am asking this question in FILM context. I would appreciate your responses.

With Best Regards.

 

[titaniumdoughnut]

Wow. Very interesting question, which I'm afraid I can't answer. Out of curiosity, what shots stand out in your mind where these things were done? Exposure, I can understand being a necessary change (either by shutter or aperture), but I can't think of a situation where you'd change the frame rate.

 

[joren]

One shot that comes to mind that uses both is the opening shot in Donnie Darko. ...where we are introduced to the important people at the school. They speed up the frame rate on each new person we meet. And they go from outdoors to indoors so I'd assume they have to change exposures at some point. Actually, this shot was the subject of a "Anatomy of a scene" program on the sundance channel. As for how you'd communicate the timing of such changes.... It would be a cue that the cinematographer and director would establish with the 1st AC or focus puller. Depending on the director/DP relationship, one would decide where each change should happen.

 

[Hoeks]

technically, you could rent a device that changes the f stop according to the fps to have a precice change of speed without seeing any change in the exposure.

However, if you use HMI lights, don't do it. You will have flicker problems

 

[the parnell]

you're better off changing shutter angle rather than apeture, apeture on most cameras ive used has been steped.

 

[titaniumdoughnut]

wait... what is shutter angle? all I knew of were aperture and shutter speed.

 

[Hoeks]

usually the shutetr angle is fixed to 180 degree (bolex has a different one) and they are exceptions. Changing the shutter angle gives you a longer(or shorter) time of exposure on each frame of the film. That results in certain effects like the Saving private Ryan opening scene effect where everything is kinda jerky.

now this was definitely not a good explanation

I should look it up myself in a book

 

[RFranco]

we try stuff like that all the time here in school to show off.

for the frame change you need a CE Base controller, and a camera that can use it. (here at school only the Arris can use it, but i think they make it for just about every camera)

a CE Base uses a crystal to synchronize it's framerate to keep a steady pace no matter what framerate you tell it to run. This way the camera motor doesn't have to worry about the speed because the base will keep it going. The base can either be told a specific framerate, or it can be input as a pullup/pulldown frame-rate (for sound and transfer purposes) or it can be set to a variable framerate using a small wheel.

as you push the wheel up the frame rate increases, as you pull the wheel down, the frame rate decreses. that's how you control your framerate.


as far as i know, no camera lets you change the shutter angle as the camera is rolling because it will damage the shutter as it rotates at a high speed. also changing the shutter angle drastically changes the amount of blur in the frame and so things will get blurrier or sharper which might look weird. changing framerates will keep the blurriness/sharpness in reference to the frame rate.


most lenses i've used, from 8mm to 35mm, do have graduated f-stops, but aren't necessarily stepped (i'm assuming by step, parnell means they click into place at each stop?) anyway, changing f-stop is just simply about rolling the f-stop this way or that as you change framerate.


as far as the director goes, these are all decisions that aren't up to him. most of the time the framing of a shot, the timing of a shot, the speed of a shot, and all that other stuff is up to the D.P. and the Camera Operator.

I know you guys really like the idea of a director saying things are going to be shot like this and like that, and getting behind the camera. but some d.p. won't let you, and especially camera operators, they will get PISSED if you keep telling them how to frame a shot. that's why you hire a D.P. and camera operator whose work you LIKE AND RESPECT.

so most of the time the director will simply say "this is the closeup" and the d.p. and camera operator will decide how close-up the close up should be.

(a famous incident of this is Francis Ford Coppola being worried that the close-ups in the godfathe were TOO close, but the D.P. Gordon Willis, wouldn't have it any other way. Franic was really worried about it, but when the film came out, the critics all commented on how amazing and brooding the "extreme" close-ups were)

so anyway, yea, directors shouldn't be worrying about all these things. if they want the camera to go from inside to outside, then that's what they should ask, and let the cinematographer worry about how to do it and when because THAT IS HIS JOB. if you want to have complete control over that, then be the cinematographer yourself.

and the framerate i could understand, and actually for a shot like that it would probably be best for the Editor, Director, and Cinematographer to all discuss the shot, because if the director goes on some tangent worrying about the slowmotion in camera, and then the Editor gets it and can't use it as he's cutting the film, he'll have to take the entire shot out and nothing pisses off the Producers more than spending a lot of time and money and days on shots that aren't going to be used.

that's how i've seen from my perspective atleast, on small shoots or fairly bigger shorts or features.

 

[RFranco]

Originally posted by Hoeks:
usually the shutetr angle is fixed to 180 degree (bolex has a different one) and they are exceptions. Changing the shutter angle gives you a longer(or shorter) time of exposure on each frame of the film. That results in certain effects like the Saving private Ryan opening scene effect where everything is kinda jerky.

now this was definitely not a good explanation

I should look it up myself in a book

actually 180 used to be standard, but not so much anymore. lots of cameras have different angles now. some are 133, some are 160, some bolexes can be 90.

Bolexes are the only cameras that allow you to change the shutter angle by simply moving a lever on the outside of the camera since they're not considered "pro" anymore.

most pro cameras have a little compartment that hides the control for adjustment and sometimes the camera won't run while it's in use just so no one will touch it by mistake or adjust it and forget about it. (we've adjust the shutter on a bolex for one shot and forgot about it and shot the rest at a different stop. oops.)

the shutter can be adjust mechanically, or even better (and more expensive) magnetically. magnetically you get more control over the angle.


changing the camera shutter angle makes thing blurier or sharper.

in saving private ryan, it's not really jerky, it's just that each frame is in SHARP focus. our eyes are not used to seeing things happen quickly in sharp focus. wave you hand in front of your face, it's not sharp is it? so once you do see something happen quickly in sharp focus, your mind gets really weirded out. it makes things seem hyper-realistic.

by the same token, if things are too blurry during each frame, the footage gets this lazy, dreamlike quality, and your mind views it as surrealist.

lots of movies used different shutter speeds. music videos have been doing it since the early 90's. i never get why Saving Private Ryan gets so much attention for doing it. i guess because lots of people have seen that movie?

if you want to see what blurry, large shutter angle looks like, watch Michel Gonrdy's video for How Does it Feel.


ALSO, one last thing: in film, and especially with the big big film cameras, there are lots of things that will affect exposure, and lots of things that can be adjusted, but in terms of this conversation here are some of them:



SHUTTER SPEED =

this is how fast the shutter rotates to take the pictures. the shutter makes on revolution every time a frame is photographed, it is usually understood in terms of TIME. so if you are running film at 24 frames per second, that means the shutter turns 24 times a second.

so by using the shutter angle, it is the amount of time the film is exposed to light as the shutter makes its revolutions in ONE second.

here is how you figure out the exposure time:

because the shutter is a solid, circular disc the whole is 360 degrees. If the shutter angle is 180 degrees, that means HALF of the shutter is missing in order to allow light in, and the other half keeps light out. this is to allow the film time to move out of the way for the next frame.

if the disc is making 24 revolutions per second , then it is open half the time, and closed the other half (since it is a spinning circle) within ONE second.

so, 24 frames per second means 24 pictures per second. 24 pictures per second can be written as a fraction: 1/24. so each picture is taken during 1/24 of a second.

BUT, because our shutter is only open HALF the time, we actually have to cut our fraction in HALF as well, and so we end up with 1/48.

our shutter speed is then 1/48 of a second with a 180 shutter. with a 133 degree shutter, it changes to 1/60 of a second i believe. (this is important because your light meter needs to know what the exposure time is going to be, no matter whether you're shooting on film or video, since the intensity of your lights depends on the exposure)


FRAME RATE =

this is how fast the frames are running by. using the same example as above. imagine our camera had a 180 degree shutter, but instead of 24 frames per second, it was running at 60 frames per second.

initially our exposure time would be 1/60 of a second, and half of that would be 1/120 of a seocnd. so now we need LOTS of light, since we are cutting out quite a bit. this is why slow motion in camera is hard, you needs lots of light.


SHUTTER ANGLE =

most shutters are round, and so the area that is removed to allow light to hit the film is measured in angles. 180 used to be standard, but new cameras (depending on their function) physically need different shutter angles because the engineers have figured out what's best or what's feasible. that's why it's important to read the manual and know what camera company, year, AND type you are using.

so for example. let's say you are running at 24fps with a 180 degree shutter. your exposure time would be 1/48.

but if we change it to a 90 degree angle, it would be 1/96. that's a lot less time, and so our picture will be SHARPER, since it is freezing the action. much like in sports photography.

if we went to a 45 degree shutter, our exposure time would be 1/192, even more freezing of the action.



some other things that affect exposure is APERATURE and FILTERS, as well as any special LENSES you may be using.

filters and lenses, the manual usually tells you how much light they cut out in the Specifications section.

see these are all things to worry about, which is why it's not a director's job to choose when and where the framerate is going to change, or when/where the aperature is going to change.

that's the Camera department's job. and the ones that are good at it get paid WELL.


also, if you guys think this is all just film stuff you don't need to learn, you're wrong, because video cameras work on the same principles.

YES, you can see on a video camera how it's going to look without knowing what your aperature is or what you're shutter speed is or what a shutter angle is.

but without knowing those things you can't plan your shots, compensate for lighting/weather conditions, or do trick photography that makes us go OOOH and AHHHHH.



none of the things i've mentioned in this post are film-specific, they are just the mathematics of light and exposure.

 

[titaniumdoughnut]

Thanks! Most of that went waaayy over my head, but thats what film school is for I suppose

I DO remember shutter angle from After Effects, it controlled how much motion blur there was on moving layers.

 

[Hoeks]

yea, listen to RFranco, nothing to add

Bolexes are the only cameras that allow you to change the shutter angle by simply moving a lever on the outside of the camera since they're not considered "pro" anymore.


Doesnt the panavision gold 2 have such a lever? Not sure anymore. I dont like to mess with shutter angles unless I am shooting a monitor

 

[NotaMono]

I've seen these things done many times, and under many different circumstances. There are now several cameras on the market (Starting with the Arri 4-35A) that can automatically adjust the shutter angle to compensate exposure during a speed ramp. More commonly in low-budget land the 1st A.C. will rack the aperture in tandem with the ramp mechanisim. This strategy isn't as precise, but can be done faily seamlessly (You'll need a pretty skilled A.C., though). You'll need to be aware of the consequences of either strategy before hand (Most of which have been brought up here) specifically that a change in shutter angle will effect the motion artifact, and a change in aperture will change your depth of field.

Not all cameras are variable speed. Those that are have different control mechanisms for handling this. Also, most cameras that are quiet enough to do sync sound are limited in their variable speed capabilities. For this reason I'd recommend you figure out what, specifically, you want to do before making your camera decisions, and co-ordinate with your cinematographer as to what your best options are.

Originally posted by bhangima:
Assuming you are the director, how would you communicate to the Cinematographer on the exact timing at which the change (in FPS and Exposure values) to take place?

Hopefully, you'd have the time and money to run a couple of tests before hand to help you co-ordinate. Regardless, just discussing it with your cinematographer can usually result in whatever effect and timing you want. Going off speed will result in the un-syncing much of your sound anyway, so you can usually give an audio queue to the A.C.(Usually there's no need to, though).

Originally posted by the parnell:
apeture on most cameras ive used has been steped.

I can't say I've ever encountered that on an MP lens. Lots of times on still lenses, though.

Most fixed shutter cameras I've encountered have been 172.8 degrees. The logic here is that this is an HMi/Fluorescent safe angle at 24fps in 50hz countries, and has minimal impact on exposure/motion artifacts vs. a 180 degree shutter.

Originally posted by the RFranco:
as far as the director goes, these are all decisions that aren't up to him.

Hmmm.... I suppose it somewhat depends on the cinematographer, but I personally believe it's the D.P.s responsability to give the director whatever he/she wants, or as close to it as can be achieved. Don't get me wrong, it's a cinematographer's emperative to explain to a director why something doesn't/can't/won't work, but it's ultimately the director's call in regards to pretty much anything on set. The Gordon Willis days were slightly different for a myriad of reasons, but these days most cinematographers would find themselves fired very fast if they started refusing directors orders. One of my professors has a good saying: "You can't keep a director from making a bad film, you can just suggest that they don't."

Originally posted by the RFranco:
i never get why Saving Private Ryan gets so much attention for doing it.

I think it's probablly because the effect is used with great skill to help move the story forward in that film. Often times the effect is just used as style for style's sake.

Nota "Got more ramps than Evel Knievel" Mono

 

[Stu Marks]

So what would the difference between shooting a scene at a shutter speed of 1/48 and shooting the same scene with a shutter speed of 1/24 with a shutter angle of 180 degrees. Both would yield an exposure time of 1/48, so what would the difference be?

 

[joren]

Stu, my understanding is that the shutter speed is determined by the shutter angle for film cameras. That is to say, you set the shutter speed by setting the shutter angle. They're not independent of each other. In 24 fps, if the shutter were open 180°, which is (or was) standard, it would be open 1/2 of 1/24th of a second...which is 1/48th sec. If it were open 90°, it would be open 1/4th of 1/24th of a second ... which is 1/96th sec.

It's nice to see you back posting again, Rob. Almost thought you fancy AFI students were to good for SF.com. Now you can correct all my misinformation.

Now, what happened to Alejandro?

 

[Stu Marks]

I still don't get it...I thought shutter speed was the speed at which the shutter opened and closed, determining whether you get a blurred or sharp image. But you're saying that shutter speed is the combination of this speed, and the shutter angle. But it doesn't make sense to not have these two settings independent of each other....BAH I'm confused

 

[Hoeks]

Alejandro? I do know a great gaffer named alejandro

 

[Stu Marks]

I guess what I'm saying is that I know, at least with still film cameras, your shutter speed is not restricted to the number of pictures you're taking...meaning a film camera's "shutter speed" doesn't always have to be (as all the examples in this message suggest" 1/24 of a second. It can be faster. Because we're talking about how long the film is exposed to light. So couldn't the shutter speed be faster, or slower than 1/24? Maybe I'm misinterpreting what is being said...someone please clear this up? I understand that, mathematically, a picture is being taken every 24th of a second at 24fps film, but how does the length of time the shutter is open factor into this and how does that then relate to this strange vaguely explained "shutter angle"?

 

[joren]

Stu, no one yet has attempted to describe the shutter angle--just how it relates to shutter speed (or RFranco tried briefly, and I'll give it another shot, adding to what he said). And you are wrong about still cameras. My digital SLR has a continuous frame rate of 4 frames per second. But, that is only if the shutter speed is fast enough to support that. If I set the shutter speed to, for example 1/4th a second, it will slow down because even though there is enough time in a second to expose 4 frames, you still need time to open and close the shutter, advance the film, meter and focus, etc. Try setting your shutter speed on your camera to 1/4th a second and see if it slows down how fast you can continuously take pictures.

Here's my attempt at clearing up your confusion of shutter angles:
In still film cameras, there is a horizontal shutter that opens, and holds in it's "open" positions for an amount of time set by the user, then closes. In motion picture film cameras, there is a wheel between the lens and the film that is constantly turning. It is constantly turning one revolution per frame per second. So, at 24 FPS, it rotates 24 times. but this wheel isn't totally solid, it has a wedge cut out of it (like an apple pie with a piece of pie missing). The shutter angle is basically how large the missing piece of pie is. When the wheel turns, the film gets exposed when light passes through the empty wedge in the wheel. When the wheel is turned such that it is blocking the image from getting to the negative, the camera advances the film one frame. So, when the wedge in the shutter spins around the next time, allowing light through to the negative, the next frame will be in position. This is how motion film cameras work, generally. This is very different from how video cameras and how still film cameras work. You shouldn't compare them. So, the shutter is this wheel. You set the length of time the film is exposed by adjusting the shutter angle. On 24fps, 180° is 1/48th sec. 90° is 1/96th sec. 45° is 1/192th sec. With some cameras you can go longer than 180°, but you start to get unnatural motion blur. That's it. Shutter speed is determined by shutter angle. The only shutter is the spinning wheel with the wedge missing.

 

[Stu Marks]

Ok I think I understand now. Thanks a lot.

 

[RFranco]

hey i just saw Raging Bull tonight again (amazing DVD they made for it), and while he is fighting Sugar Ray, there is a shot where he walks back, it slows down as he eyes Sugar Ray, then goes back to normal speed as the bell rings again.

really great shot. although i think it might've been a post effect, but only because the editor uses a lot of stuff like that in post. but it could've been done in camera.