Exposing + Native ISO

[Mark L. Pederson]

Looking back I don't think I've every worked with a DP who selectively changed a film stock's ISO rating dependent on a particular scene (INT/EXT/DAY/NIGHT). Maybe if said DP was pushing or pulling the stock via processing but that will actually affect the film's exposure response, something that doesn't happen with cameras like DRAGON.

I worked on tons of movies with two film stocks - one for interiors and night and one for daylight. That was pretty much the norm at the time.

 

[Mark L. Pederson]

Phil Holland has a sekonic L-478, maybe he can tell us his experience using it.

Let's do that.

Yo Phil -

Should I buy that L-478?

 

[Phil Holland]

For simplicity's sake a Sensor's Base Sensitivity, Native ISO, Base ISO, Balanced ISO, or simply ISO (as one would find on a can of 35mm film) is the same thing. In terms of "scene exposure" ISO is a camera's or film's mid exposure point where there is an EVEN distribution of usable stops above and below middle grey. This standard definition has been used for about 100 years. I'm still perpetually confused why RED prefers to define their cameras with an ISO Range (200-2000 w/ Dragon) instead of a nominal exposure mid-point.


Phil, in your opinion, what have you found to be DRAGON's mid-point ISO (ie: 8 over / 8 under)?

It's more than 8 over and under, which is why this is a bit tricky. It's just a bit more. Based on the latest calibration and OLPF I have measured a hair over 18 unique stops of clear separation between tonal full stops. However, that was flat REDlogFilm. Under a normal viewing gamma you are looking more into the 16.3-17 stop range of usable captured dynamic range, though that extra "goodness" is still there and accessible.

Given that it's the difference of dividing 16.3 and 18.alittlebitmore by two. So in that regard the Base ISO again falls between that 1.3 stop range I mentioned ealier. ISO 640-1600.

And if you're interested I feel this is why many will be shooting ISO 640, 800, 1000, 1250, and 1600 on Dragon. You can play devils advocated and just extract the center value from that and say ISO 1000 if you want (though not the best thing to do). That allows for aproximately 2/3rds of a stop variance on either side. So think about what that would mean in terms of absolute clip, readable highlight and absolute "Super Black", measurable tonal separation in shadows.


Long and the short of it, the Base ISO of Dragon falls within ISO 640-1600 as of the latest calibration. If you want a what I would describe as a hard sweet spot number I'd say it's about ISO 1125 (weird number) based on all that data.


Will shooting at only that ISO get you the best results in every situation? Not necessarily.

If you are curious a good chunk of those shooting abroad with Dragon on rating for ISO 800 and going with that.

Shooting at lower ISOs below 800 helps produce a cleaner look and distributes more dynamic range "weighting" in the shadows. Vice versa, shooting at a higher ISOs above 800 places more dynamic range in highlights and you will see more "texture" across shadows and midtones. Nothing new there.

To note something. The published cinema ready usable range of ISO 250-2000 is a 3 stop range. ISO 640/800 fall in the middle of that range. Just something to note.


Also, side note as a particular film stock was mentioned earlier in this discussion. Even Kubrick and Larry Smith pushed 5298 +2 stops on Eyes Wide Shut. I've had crazy, crazy conversations with filmmakers over the years about what "digital films" should look like. I've also done many "look" tests. Red cameras were once marketed as a "digital film alternative" and I do think this explains a bit of their popularity. Shooting, rating, and exposing for different ISOs should be considered like shooting different film stocks. Though obviously digital isn't exactly as noisey. If you enjoy a cleaner look favor lower ISOs. If you want subtle textured character higher ISOs might be worth exploring. It's up to you. With ISO you are merely rating your midtones and in effect subtly defining the overall look of your material.

 

[Phil Holland]

I'm an incident guy - only because that's what I had in film school. That's what I "know". I could not afford a reflected meter.

I actually want to buy a new one - I think I'm gonna go Sekonic L-478D LiteMaster Pro - http://www.sekonic.com/products/l-478dr/overview.aspx

Phil Holland has a sekonic L-478, maybe he can tell us his experience using it.

Yo Phil -

Should I buy that L-478?

I like it overall. The weird bit is that the spot meter is something you have to "attach" and isn't always on. I am also mostly an incident meter guy, though I use the spot a good deal on more visual effects and technical related tasks. The spot meter is a 5 degree meter and I know some have criticized that, I've oddly enjoyed it's "broadness". Touch interface is sometimes a bit tricky when attempting to scroll values, but beyond that I like it a lot.

It's compact and has a nice big screen and that's very useful.

 

[Mark L. Pederson]

I like it overall. The weird bit is that the spot meter is something you have to "attach" and isn't always on. I am also mostly an incident meter guy, though I use the spot a good deal on more visual effects and technical related tasks. The spot meter is a 5 degree meter and I know some have criticized that, I've oddly enjoyed it's "broadness". Touch interface is sometimes a bit tricky when attempting to scroll values, but beyond that I like it a lot.

It's compact and has a nice big screen and that's very useful.

Thx Phil. Hmmmm ... based on that review I will need to do a "hands on" comparison with the L-758Cine.

 

[Adrian Jebef]

Shoot a test, using a spot meter, in order to evaluate/sync it with your chosen iso, and establish the iso's clipping point and max black with detail, it is then easy to PLACE values up and down that scale with impunity - you will never fear clipping or losing valuable shadow detail ever again. The power of the reflected light meter lies in its ability to show us relationships between every subject value - and since we know it reads everything at mid gray (18%) we can then see where values fall on the scale, and alter their position to suit our needs - as long as we have tested and accurately established the scale, just like the chart Adrian posted.
Take the iso 800 sample on the chart, we can see that anything at/above 7.4 stops above mid gray is clipped, and it's easy to see which scene values fall in or out of that zone if one is using a spot (reflected light) meter.

Amen, Bill. It is as easy as you've made it out to be. This is why I find it so confusing that there are shooters like Mark who selectively change ISO on their meters and cameras.

If you test your camera (as an example DRAGON) and find it's ISO to be 800 via your own exposure tests or perhaps by the ISO printed on the box, what do you gain by changing that ISO later? You've only got 16 Stops. You don't get any extra stops in your highlights or shadows when you change to ISO 200 or 2000 on your meter or on your camera. Middle-Grey is the same. It doesn't change. It's a constant. Just because you are shooting a Day Exterior and decide to change your ISO to 400 that still doesn't change your "scene referenced" 18% Grey card. If proper exposure via your meter and scene referenced 18% Grey at nominal ISO 800 is T5.6 for a particular shot just because you change ISO to 400 doesn't mean proper exposure is now magically T4. It's still T5.6. When you change ISO to 400 and expose at T4 you are in effect over-exposing your shot by 1 Stop. To any photographer or cinematographer I'd think this would be important.

Thoughts?

 

[Adrian Jebef]

I worked on tons of movies with two film stocks - one for interiors and night and one for daylight. That was pretty much the norm at the time.

Yeah, but I bet those two stocks had two different ISOs. Maybe 250D and 500T? The DRAGON has just one ISO. It is one stock, not 2 or 3 or 100.

 

[Mark L. Pederson]

The DRAGON has just one ISO.

By what definition? And what form of measurement? And what tolerance for noise?

I'm sorry, but as far as I'm concerned - it's a range. And I personally see creative and technical advantages for rating it differently for different situations and subject matter.

If you believe that one should only rate the camera ONE way - with ONE ISO - you can do that.

 

[Jacobo Martinez]

Yeah, but I bet those two stocks had two different ISOs. Maybe 250D and 500T? The DRAGON has just one ISO. It is one stock, not 2 or 3 or 100.

Correct me if I am wrong, but from what understand, ISO in RED is a Look, a feel, a tool for the story.

 

[Jacobo Martinez]

Sure Adrian - this is exactly what I did the first day I got a Dragon -



I do some simple tests - I start with 800 - so I set my light meter to 800 - I place a subject holding a color chart against a neutral background- I take an incident reading next to the face of the subject - I open up one stop for skin tones (caucasian) - and I shoot a shot. Then, I bracket - + and 1 to 4 stops over and under. Then I look at the R3D files in RCX - push and pull them. And I mentally process what I see - based on my subjective impressions of what I like as a look and my personal tolerance for noise.

Mark, I got confused from the comment you made about exposing with an incident meter. It is highlighted in green. When you use incident meter, the value the photometer meter would be the correct exposure for middle gray. You dont have to stop 1 stop for caucasion skin. If you use a spot meter and read the caucasian skin tone, than you would add one stop to the reading. Am i wrong?

 

[Bill Anderson]

I use the one degree spot almost exclusively. Why, because it can show every value in a scene, and consequently you know the relationship of each value with another's, and their relationship with the EI scale; thus, it allows you to place those values exactly where you want them on that scale. You can place your highlight values just this side of clipping every time you desire, without a look at a monitor or scopes and what not. Same goes for shadow detail. You want to check your lighting ratio or use an incident meter? use your hand: place your hand where you would place your incident meter and, using your spot meter, take a reading and open up one stop. Done. Or use a gray card and don't open up one stop ( :

Just one more way to skin that cat I guess.

 

[Mark L. Pederson]

This is why I find it so confusing that there are shooters like Mark who selectively change ISO on their meters and cameras.

Read post #54 again in this thread.

 

[Adrian Jebef]

By what definition? And what form of measurement? And what tolerance for noise?

I'm sorry, but as far as I'm concerned - it's a range. And I personally see creative and technical advantages for rating it differently for different situations and subject matter.

If you believe that one should only rate the camera ONE way - with ONE ISO - you can do that.

I'm referring to history here, Mark. ASA / ISO / Native Sensor Sensitivity / 18% Grey are all constant values per their respective host (ie: film stock, digital camera, scene referenced middle-grey). They do not fluctuate. These values have always been defined as the middle-point or middle-value that best expressed an equal distribution of dynamic range both above and below said value. There's always a range of DR but the mid-point is forever fixed.

I would think it more difficult to work your exposure based off of different ISOs than by simply sticking to the Base ISO (as Phil likes to call it). If you know your camera's Base ISO then it's a breeze checking scene exposure values with a light meter. If you're above or below 8 Stops you're in trouble. If you're within tolerances then you're good. But if you all of a sudden change to 200 ISO now you've got 12 Stops below but only 4 Stops above. Shooting a Day Exterior this way could be easily detrimental. Plus you'll need to constantly refer back to an ISO/DR chart that shows the redistributed above/below mid-grey exposure stops when ISO is changed in camera. Seems a bit complicated way of working when the fundamentals of ISO and exposure are, in fact, super simple.

 

[Adrian Jebef]

Correct me if I am wrong, but from what understand, ISO in RED is a Look, a feel, a tool for the story.

Only if you are using ISO as a "development" value. When exposing on set for a specific scene the ISO is a fixed value.

 

[D Fuller]

OK. Interesting. What kind of meter do you prefer to use? Incident or Spot?

I'm interested in those of you who continue to use light meters w/ digital cinematography as I've basically all but tossed mine years ago. Looking back I don't think I've every worked with a DP who selectively changed a film stock's ISO rating dependent on a particular scene (INT/EXT/DAY/NIGHT). Maybe if said DP was pushing or pulling the stock via processing but that will actually affect the film's exposure response, something that doesn't happen with cameras like DRAGON.

But it does. You push or pull the development of the r3d just as we did with film. And it changes the image's response, just as it did with film.

 

[D Fuller]

Only if you are using ISO as a "development" value. When exposing on set for a specific scene the ISO is a fixed value.

But how do you do one without doing the other? Raising the ISO on a Red camera is very much like push-processing film. You under-expose, knowing that you will develop the exposure in a particular way when you process the footage.

 

[Jacobo Martinez]

But it does. You push or pull the development of the r3d just as we did with film. And it changes the image's response, just as it did with film.

+101

 

[Jacobo Martinez]

But how do you do one without doing the other? Raising the ISO on a Red camera is very much like push-processing film. You under-expose, knowing that you will develop the exposure in a particular way when you process the footage.

Exactly the same! 100% agree, iso is a creative desicion that serves the story.

 

[Adrian Jebef]

Read post #54 again in this thread.

Mark is Correct.

And the application of this is called shooting the "Toe" or shooting the "Shoulder",

Its a common practice for film guys through history until the Vision Stocks came out. Most DPs shot only 200TASA (5293) stock and never set there light meters to 200ASA ever.
They would shoot day and night because the early 500ASA was so grainey or as we say now noisey (sad that grain is called noise, so negative)and shooting different stocks was always jarring in the edit.

If you are going for a darker look, night interior, you shot test for the toe, the bottom of the stocks DR and sensitivity. You are going for blacks, skin exposure and protecting grain,not concerned with highlights, it not interior and you can put practicals on dimmers.

You might find that rating the film at 500 gave you much better results because you found some extra DR in this chemical batch of film which ranged quite a bit in the 90s. From 200ASA to 500ASA is a doubling of light. That is a huge amount a light at 200ASA you don't need now.

And vice versa with shooting "shoulder."

If you are going for skies or highlights or windows, you shoot and test for the Shoulder. And rate the same stock accordingly maybe at 100ASA to get that cloud detail.

Just because DR is there, doesn't mean that that info has to go on the screen, you get to choose, that's your call.



find your Toe or Shoulder sweet spot.

I decide to shoot the shoulder or toe and ETTR.
I never had a problem getting a black in post so I tend to open up for Night interiors and stop down for day exteriors

If 800 is clipping, always ND if you can to the native rating of the camera that's always the best, if youre out of ND and you need to roll the ASA down to hold the skies just do it. Your contrast will go up, so pull some out in your look settings,

Though this is true in respect to exposing a film negative, there is no "knee" or "shoulder" in digital cinematography. Film responds logarithmically, digital CMOS sensors like all of the RED cameras respond linearly. Though a gamma curve can be interpolated from a digital camera's linear code values the sensor has no log-esque response to scene referenced exposure the way film negative does. Though we may want to equate the two, the truth is they are basically complete opposites when it comes down to exposure response.

 

[Zeb B]

I expose Red with very similar thinking, and that's where ISO has become important again -- not the camera's ISO setting, but ISO as a reference for light levels in front of the lens. I know that the sensor is about 320 ISO native, but I don't love the completely-clean image I get at 320 for most things. At 800, I get a bit of very pleasant noise, which I like, and the added benefit of some headroom that lets me roll the highlights off nicely. But for things like tabletop and package shots, I usually want a "fatter negative" with more color and a bit less noise, so I expose for 640 or 500, knowing I have to watch the highlights more carefully, but knowing that it will do things to the image that I want. Or as with Gunleik's image above, I can underexpose and get an image where darks cluster together and mix with noise a bit, and the hilights occupy most of the long slope of the tonal curve. All with a sensor that has a fixed response.

thank you