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Pushing/pulling


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#1 Petter Englund

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Posted 06 November 2016 - 06:50 AM

Hello,

 

I'm new to shooting on film and have a question about pushing / pulling a negative in processing!

 

Let's say I want to push my negative 1 stop for artistic purposes (more grain etc.)

From what I have understood, the way I would do that is rate the ASA of the film stock I'm using 1 stop over its native.

So if I'm shooting on Kodak 5219 500T, I would simply rate it at ASA 1000.

 

My guess is that the lab I later was sending the negative for processing at, would take my ASA rating in consideration (unknowingly of its native ASA rating) and automatically push it 1 stop.

 

Is this correct?

 

But then why is there an extra fee for push/pull processing at the labs?
If they don't know the film stock's native ASA rating, then how would they know if the stock were being pushed or pulled?

 

Or does this work in another way?

 

Best regards,


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#2 Michael Rodin

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Posted 06 November 2016 - 07:14 AM

In push processing film is ran slower through baths of ECN2 chemicals and gets overdeveloped. Technically nothing to do with the EI. Labs don't use EIs, they judge negative by densities.

Pushed neg is more contrasty and builds up more density so you can underexpose it when shooting but still see shadow detail and adequate density on processed film. So you are able to light to a higher EI.


Edited by Michael Rodin, 06 November 2016 - 07:21 AM.

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#3 Petter Englund

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Posted 06 November 2016 - 07:29 AM

Okay, I see...

So my personal rating of a film stock is just for the calibrations of my light meter / exposure tools?

So in other words, me telling a lab to push 1 stop means they will simply aim for another density in my negative and nothing else?

 

What if a roll has different densities across?

Is that when best-light or scene-by-scene developing comes to play?

 

Experimentally --

If I were to expose a negative correctly for its native ASA and tell the lab to push 1 stop - my final result would be a somewhat overexposed image?

 

Thanks for the reply!

Helps a lot!


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#4 Heikki Repo

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Posted 06 November 2016 - 08:06 AM

Hi Petter, you are correct, your personal rating of the film stock is only for your use when metering.

 

As for processing, unless you specify some special processing (push/pull) they'll just process it normally. You really cannot order push/pull for some parts of film unless it is on a separate core/spool. There is no best-light or scene-by-scene developing. You yourself have to know how you have exposed your film and order accordingly.

 

If you expose a negative correctly and ask for 1 stop push, it'll be overexposed. :)


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#5 Michael Rodin

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Posted 06 November 2016 - 09:35 AM

Okay, I see...

So my personal rating of a film stock is just for the calibrations of my light meter / exposure tools?

 

Yes, really. In pre-production you do exposure tests, shooting the same test scene(s) (representing what's the most important in your film, like skin, costume, maybe snow or foliage) with normal exposure based on EI written on the can, then with +1/3, -1/3, +2/3 stop and so on. Then you process and scan on the exact same system you'll use in post. Project and choose a base exposure which gives you the best image and see how much you can deviate from that (what's you usable latitude).

 

For example, you found normally processed 5203 looks best on Arriscan exposed 2/3 stops over (real-world example), so you rate it EI32.

 

That's the "proper" way of finding the EI but considering the huge latitude of modern neg stock you'll never be way off with a recommended EI. And with basic sensitometery knowledge and some experience you'll pretty precisely predict what over-under exposure and push-pull will to to your image.

 

So in other words, me telling a lab to push 1 stop means they will simply aim for another density in my negative and nothing else?

They'll simply run their machine slower, so that neg will ideally get 0.15 points denser.

 

0.15 because exposure difference of 1 stop translates to optical density difference of 0.3D and with a coarsely 0.5 gamma (which means 2x tone compression) of a negative it equals 0.15D.

 

Sometimes you desperately need that density.

Say, you shot the leading lady on 5219 rated 500T at you Zeiss Standarts' maximum T2.1 but there wasn't enough light and her face read T1.4 on a spot meter. You don't want her face whole 2 stops under because it'll be like 0.4 density (it's murky mess which gets you fired).

So you either request a push-1 and get a 0,55D with reasonable grain/contrast or do a push-2 and get "perfect" 0,7D, albeit very contrasty and grainy.

 

When you go for a "pushed" look, it's not about the density but contrast and grain.

 

BTW, pull-process is used much less and mostly for "artistic" reasons rather than technical. Overexposure doesn't really ruin your images unless you hit 4-5 stops over.

 

What if a roll has different densities across?

As long as all the shots print/scan well and yield a quality image, it's OK.

 

If not, and you're stuck with a mixture of over- & underexposed footage on a roll, you decide how much UNDERexposure you can tolerate on the underexposed scenes and PUSH accordingly. Don't worry about overexposing other stuff on the roll unless there are important details shot 4 stops over (say, window views). But why did you do that if they're important?

 

Usually you keep some densities (like actor's faces) consistent and ensure there's always some black and some highlights in any frame. But everything other changes from one lighting setup to another. It's OK for a subject to render different densities under different light.

Even a face can go from -1 to +2,5 stops relative to middle gray in a really bold movie (but unlikely within a roll). Just make sure the audience sees the eyes (at least some reflection in them) in your portrait CUs/middle shots.

 

Is that when best-light or scene-by-scene developing comes to play?

There's no best-light processing, only best-light print and telecine.

If you're in real trouble, you can try to splice your roll into parts and process them differently. Theoretically possible given you had a nice complete camera report. Don't expect your lab to do it!

 

If I were to expose a negative correctly for its native ASA and tell the lab to push 1 stop - my final result would be a somewhat overexposed image?

It'll be 0.15D more dense. Plus grainier and more contrasty, won't have a noticeable "overexposed" look (like overexposed video would).


Edited by Michael Rodin, 06 November 2016 - 09:44 AM.

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#6 Michael Rodin

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Posted 06 November 2016 - 10:00 AM

Can't edit, so...

 

"If not, and you're stuck with a mixture of over- & underexposed footage on a roll, you decide how much UNDERexposure you can tolerate on the underexposed scenes and PUSH accordingly. Don't worry about overexposing other stuff on the roll"

Meant overdeveloping.

 

Also, when doing exposure test, don't forget to include a grayscale in the scene, so you can see when you're reaching into the toe or shoulder portions of the characteristic curve.

And you can do a sensitometric lab test. The lab will expose a row of frames on a 2 meter filmstrip cut from your roll, each to different level of light, then plot a characteristic curve and calculate an ISO for you.


Edited by Michael Rodin, 06 November 2016 - 10:01 AM.

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#7 Petter Englund

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Posted 06 November 2016 - 10:00 AM

Michael,

 

Thanks for the detailed reply!

 

I guess me coming from the digital work gives me a false idea of what real film looks under- and overexposed...
But it's not the first time I've heard that overexposing film doesn't make it look "overexposed" as in the digital sense.

 

Regarding you answer to the last question -- 

In other words, comparing the exposure average value after a digital scan of 1.) a correctly exposed and processed negative with 2.) a correctly exposed but pushed 1 stop negative -- would more or less have the same reading and only differ in graininess / contrast ?

 

 

 

Practically, I want to rate my Kodak 5219 500T rolls at ASA 1000 and push it 1 stop in processing for images both during night and day (I want more grain and contrast).

It won't be a problem to purposely underexpose 1 stop during the night when it's dark, but it will be much harder during the day because there is so much light and my K1000's fastest shutter setting is 1/1000 (and I don't like to shoot on f/11- f/16).

 

But since a film negative is not very sensitive to overexposure - do you think I'll get away with purposely overexposing 2-3 stops for my day shots (allowing me to use a lower f-stop) and still pushing 1 stop in processing? The thing I want to achieve is to have the same roll in the camera and not have to change it every sunset and sunrise.

 

 

Thank you once again for the reply!


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#8 Michael Rodin

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Posted 06 November 2016 - 10:35 AM

Regarding you answer to the last question -- 

In other words, comparing the exposure average value after a digital scan of 1.) a correctly exposed and processed negative with 2.) a correctly exposed but pushed 1 stop negative -- would more or less have the same reading and only differ in graininess / contrast ?

 

(2) will get you a brighter positive image on a scanner since it's more dense.

Once you bring it back in brightness to match (1) using printer-light-like controls (i.e. "exposure" in Baselight, "master offset" in Avid Symphony) you just get a more grainy/contrasty/saturated image.

 

 

Practically, I want to rate my Kodak 5219 500T rolls at ASA 1000 and push it 1 stop in processing for images both during night and day (I want more grain and contrast).

It won't be a problem to purposely underexpose 1 stop during the night when it's dark, but it will be much harder during the day because there is so much light and my K1000's fastest shutter setting is 1/1000 (and I don't like to shoot on f/11- f/16).

That's why we use NDs.

 

But since a film negative is not very sensitive to overexposure - do you think I'll get away with purposely overexposing 2-3 stops for my day shots (allowing me to use a lower f-stop) and still pushing 1 stop in processing?

Again, why not just put an ND on camera? NDs are straightforward on film, no need to worry about IR pollution. Just get quality filters for the movie. There's 1) Schneider 2) Formatt and Tiffen, plus some specialty firms like Mitomo. Cokin and cheap Chinese filters are useless.


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#9 David Mullen ASC

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Posted 06 November 2016 - 10:48 AM

Push processing (increased development time) increases density.

 

More exposure increases density.

 

So in theory, a one-stop push process but a normal rating on your meter would give you the same final density as if you had processed normal but overexposed by one stop.

 

A one-stop push combined with a one-stop underexposure would give you a normal final density (more or less.)

 

You need heavy ND filters for your daylight shooting.  You should expose a negative for the effect you want, not overexpose everything just because you aren't carrying ND filters.  If you want to overexpose your daylight footage by two stops deliberately, that's fine -- it may actually be a good idea for other reasons -- but don't do it just because you aren't carrying ND filters.  Same goes for the shutter angle, you should use the shutter angle you want for the motion blur you want, not because you aren't carrying ND filters.  

 

The sunny 16 rule in photography already tells you that you will be at an f/16 in direct sunlight if the ASA rating is the same as the shutter time over 1 (i.e. 50 ASA at 1/50th, for example.)  So with 50 ASA, you almost need ND filters in harsh sunlight... you definitely need them on 250 ASA stock or faster unless you are only shooting at magic hour or in heavy overcast weather or deep shade.  At 1000 ASA, you're going to need at least an ND1.5, ND1.2, ND.9, ND.6, ND.3.


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#10 Petter Englund

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Posted 06 November 2016 - 11:33 AM

Thanks for the responses!

I'm just trying to understand the fundamentals of film vs digital when it comes to terms like density, push/pull processing etc.

I'd like to know as much as I can about my variables before my first film rolls arrive in my post box.

 

Of course, ND's etc are vital tools for fast film stock.

 

From what I can understand, the same density of two negatives do not mean they necessarily have the same characteristics. 

 

For example in the example above (from David Mullen), the one-stop pushed negative but a normal rating on the meter would have more grain and contrast compared to the normally processed negative that was overexposed by one stop -- given its captured under the same circumstances -- despite they have the same density?


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#11 Michael Rodin

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Posted 06 November 2016 - 11:49 AM

To judge how film reacts to light, you look at its characteristic curve. A density is just a point on that curve corresponding to some specific exposure.

So a normal and an underexposed/pushed negatives can both have faces at 0,7D but densities in shadows may be very different - the pushed film turns a steeper characteristic curve (hence the higher contrast).


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#12 David Mullen ASC

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Posted 06 November 2016 - 11:51 AM

Yes, density is a different thing than grain size or contrast (gamma).  

 

You could, for example, shoot on 50 ASA film, overexposed by 2-stops and pull-processed by two stops and then shoot another scene on 500 ASA film, underexposed by 2-stops and push-processed by 2-stops -- and the density of each would be similar... but the grain and contrast would be very different between the two scenes.

 

Graininess is a bit complex... there is the grain structure designed into the original stock that determines its sensitivity -- larger grains are better collectors of photons so faster film has larger grains than slower film does.

 

Overexposing a fast stock does not make the larger grains go away since they are the first to get exposed; what happens is that the smaller, slower grains in between the larger ones also get exposed, filling in the gaps and giving you a tighter grain structure that makes the image feel less grainy, as opposed to underexposing so that only the larger grains get exposed, and the slower, smaller grains don't get enough exposure and therefore are washed away in processing, only leaving the larger grains, giving the image a coarser look.

 

Extended processing time increases gamma / contrast but it also increases base fog level, which has a slight flattening effect. Underexposure means you are capturing less shadow information and push-processing to compensate gives the information you did capture more density but can't compensate for a lack of information, so what got exposed (the highlights) gets denser (brighter) but you don't see more shadow detail, so the end result looks more contrasty.


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#13 Karim D. Ghantous

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Posted 07 November 2016 - 04:18 AM

If any of you have not yet seen Eyes Wide Shut, please do so (I bring up this film a lot). ;-) The stock was 5298, pushed two stops, for the entire picture. I haven't seen it in HD yet but that would be preferable to DVD. The film stock has long been superceded, so 5219 should look much better (I have seen Super 16mm 7219 pushed one stop and the 2K scans looked great).

 

See the top three paragraphs of this page:

 

https://www.theasc.c...9/sword/pg3.htm

 

There is also the discussion of whether you need to push at all if you are using a DI. But I will leave that to those with experience. Suffice to say that photographers do not necessarily push negative film when they underexpose it, whether it's colour or b&w, especially if they're scanning. But slide film is always pushed if you underexpose it.


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