Proper Exposure

[Bakur]

I have 2 questions (issues). And was wondering if anyone has answers.

1. Proper exposure. Our DP uses lightmeter (Seconik if I'm not wrong) and to get proper exposure (due to histogram and final results) he sets ISO to 50 (on lightmeter), when having default 320 ISO setting on camera. Because when he sets lightmeter to 320 ISO, image is always underexposed, by at least 2 stops (maybe I'm wrong about the exact number of stops). Is everyone doing like that? We have 4 cameras, Cooke lenses and nothing extraordinary, new builds, old builds, on camera, all the same.

2. We had ground from US working in our country on the movie. As I found out, during shooting, when they had less light, they were using shutter speed 1/24sec. With 24fps framerate. And they told local cameramen that image quality is not affected. Even with moving shots. So I was wondering, is that a common practice to do so? Because Red needs a lot of light, and changing shutter speed, if it does not alter image quality, maybe a good idea.

 

[Pietro Impagliazzo]

Anyone care to comment on this?

I always get boggled by these statements.
ISO 320 to ISO 50 seems like a long exposure difference.

I never really understood exactly why light meters are off with the R1.

 

[Alex Kornreich]

I set my lightmeter to ISO 250, and so do all of the gaffers I've worked with. This is because Rec709, which is the colorspace I shoot with due to it's closer proximity in exposure to RAW than Redspace, is about half a stop brighter than RAW view. You should always expose for RAW, not Rec709/Redspace. I'm convinced that ISO 320 on the light meter exposes for Redspace, which will underexpose your RAW. To demonstrate this, turn on false color, then switch back and forth between RAW and Redspace. The image is significantly brighter in Redspace.

After metering, it's imperative to double check with false color in Raw view. If you do both of these things, and everything checks out, you should be in control with your exposure, with no surprises in post.

ISO 50 will cause you to overexpose by 2-3 stops. It all depends on what look the DP is going for. However, I've never heard of anyone using a figure as low as ISO 50. I've also never heard of setting the light meter to ISO 320 causing it to underexpose by 2-3 stops. At most it should be 1 stop. It also depends how you're metering the subject (incident/reflective/spot), but that's a whole different discussion.

Regarding the shutter speed, at 1/24th of a second, which is a 360 degree shutter, motion will look smoother, or potentially less jittery. I don't think "quality" is a good word to describe it, as whether it looks good or bad is a matter of opinion. However, with that particular shutter speed, it may have more of a "video" look, which some may consider to be a negative characteristic. Again, though, it may be appealing to the DP. If it's a low light situation, then it's also possible that was the only way to properly expose it, as it gives you another stop.

 

[jimhare]

I agree with Alex. I think setting for ISO 50 will cause you to overexpose. ISO 250 is about right.

Regarding the shutter, many crews do this in low light because "they can." If you are short of time, or short of lighting budget, this may be the only way.

The effect is not so much quality as style of image. If you go back and forth between 1/48 (180º) and 1/24 (360º) it may have the appearance of going from a film camera to a video camera. This is more of a characteristic issue than quality.

 

[Bakur]

I am not DP, but believe me I know what the proper exposure is. And if crew measures light with ISO setting 320, the image is underexposed. When setting ISO 50 we get proper exposure. And by proper I mean proper, and not specific style, or look. Nothing is clipped, etc.

Setting shutter. Sorry for the wrong word quality. So the only difference is, it will look more like a video? Will it have a same look on the screen of movie theater, or just in tv?

 

[Stuart English]

Exposure check

Exposure check

I am not DP, but believe me I know what the proper exposure is. And if crew measures light with ISO setting 320, the image is underexposed. When setting ISO 50 we get proper exposure. And by proper I mean proper, and not specific style, or look. Nothing is clipped, etc.

How exactly are you determining correct exposure - as I'd agree rating at ISO 50 sounds risky, but what type of material are you shooting? And how do you filter?

 

[Alex Kornreich]

Just like film stocks, you have to do camera tests to determine ISO. ISO on film stocks and Red is more or less of a strong recommendation, it's not set in stone. It's up to the DP to determine how they want to rate the film stock/digital camera.

If the camera is properly exposing at ISO 50, I would guess there's ND6 or some other light killing filter in front of the lens, and instead of adjusting the filter factor in the light meter, the DP is using the ISO to reflect the addition of the filters.

If the camera was natively rated at ISO 50, Red wouldn't have sold 7000 cameras. It would be too expensive to rent lights for proper exposure, and therefore wouldn't suit lower budget, independent filmmaking, which makes up a huge part of Red's customer base.

 

[Kyle Connolly]

The effect is not so much quality as style of image. If you go back and forth between 1/48 (180º) and 1/24 (360º) it may have the appearance of going from a film camera to a video camera. This is more of a characteristic issue than quality.

I'd be careful about this, Bakur. If this isn't what you intended for your look to be, I find it can be quite jarring to suddenly find 1/24 shutterspeed in the middle of a film. It immediately (to my eye, anyway) gives it away as having been shot digitally, as this shutterspeed is not possible to achieve on film when shooting 24fps. You'll instantly get the look of Michael Mann's last three films (not a bad thing at all, just very unapologetically digital).

 

[Mikael Lubtchansky]

more about that 360 shutter...

more about that 360 shutter...

Just to give a bit of 'historical' background to this shutter issue (sorry for the long post, I had not enough time to write a short one)

Back on early film days, it was decided to use 24 frames per second to capture and reproduce movement from life. (before the sound era it was 18 fps but that's another story...)

So, when exposing film, 24 frames are created for each second, but since the film have to physically move from one frame to the other in the camera, a rotating 180 degree circular shutter was used to hide any light coming from the lens during film advance.
Each second was divided in 48 segments :

first 1/48th of sec : expose frame 1
second 1/48th of sec : black, film advance to frame 2
third 1/48th of sec : expose frame 2
fourth 1/48th of sec : black, film advance to frame 3
etc

So only half of the light/time/movement was recorded on film (the second half was used to advance film and send light to the optical viewfinder using a mirror on the shutter itself).
This "lack" of temporal information plays I think a very important role in the 'magic' of cinema.
The brain somehow interpolates and reconstruct the missing data and it is what creates a kind of indescribable 'poetic' movement on screen.

With CCD/CMOS on video and digital cameras we do not have this physical limitation of film moving in camera and we can expose each frame for twice as much the amount of time, so (at 24 fps) each second is divided in 24 segments :

first 1/24th of sec : expose frame 1
second 1/24th of sec : expose frame 2
etc

It is better for several reasons : no more missing movement. twice more light received

but somehow it gives those images what we call a "video look" making things look "much more real". Certainly because everything was captured... If you shoot film at 48 fps (or 60 fps like the ShowScan format) and play back at 48 fps you also get that video feeling (since it is film you still have some missing bits but you have a much smoother motion than 24 fps).

Having 100% of the time/movement captured is disturbing for most of us because our brain has been accustomed to watch movies made on film for so many years. We got used to this way of filming the world to tell stories.

Maybe future generations will prefer to watch movies with that 'video' look. With a brain fed with high fps games and 50/60fps TV things may change quickly. Michael Mann movies are shot with this technique so you can see for yourself if it is something you like or not.

This limitation inherited from old film days (that we now have to simulate in the RED by forcing the shutter to a 180deg mode, thus 'loosing' 1 stop) is, as strange as it may look, a stenght. Part of what makes a movie different from life and somehow may helps the viewer's mind to accept the fictional world described.

Shooting with no shutter (aka 360), or shooting in 3D, or with a very large sensor may create new ways of telling stories, good or bad, but if you're after that 'magic film look' from last century the receipe is : 1/48th exposure at 24 fps. So use 360 shutter wisely only for shots with little or no movement, just in case adding light or underexposing is not an option.

Mikael

 

[Pietro Impagliazzo]

I wouldn't say 1/30th and lower shutter gives a real look.

It even looks more dreamy, motion blur is exagerated, not natural.

However, monitors and projectors with 120hz refresh rate can offer great flexiblity, being able to display 24p, 30p and 60p.

So a movie can decide if it's 60p with 360º shutter or 24p with 180º shutter, or even change it between scenes, that would be awesome for aesthetic reasons, one more trick up the filmmakers' sleeves.

 

[Bakur]

Thanks for the tips!

Funny you mentioned Michael Mann's last movies, because I was amazed by the look of Public Enemies. Absolutely agree that most of the film looks very much like digital - not like film.

One more question. We had discussion for a long time regarding the proper frame rate, during shooting for TV. And personally I have a feeling that shooting on 24 fps looks more like film, then shooting 25 fps (TV version for PAL). Is it just superstition or this one frame does make a difference in movements, and makes film look?

 

[Bakur]

How exactly are you determining correct exposure - as I'd agree rating at ISO 50 sounds risky, but what type of material are you shooting? And how do you filter?

Drama series for TV. I will submit some raw stills later, to demonstrate exposure measured with light meter set on ISO 50.

 

[Mohammed El Sharqawy]

One more question. We had discussion for a long time regarding the proper frame rate, during shooting for TV. And personally I have a feeling that shooting on 24 fps looks more like film, then shooting 25 fps (TV version for PAL). Is it just superstition or this one frame does make a difference in movements, and makes film look?

not that you can recognize.. 25p and 24p are very close on how they look on the screen.. you can feel a little difference if you converted 24 to 25 or vice versa,, like a jitter every second.. that's why telecine for 25 fps runs the film at 25 fps while it was shot on 24.. then back to 24 fps on the editing station to decide whether to stretch the audio or get timecode/edgecode db for pull list cutting and so on.. (film workflow..)