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"Pushed two stops"

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Winston A. Cely
"Pushed two stops"
on Sep 24, 2017 at 1:38:58 am

So, I'm watching Eyes Wide Shut, and I know the film was pushed two stops in post to enable Kubrick and Larry Smith to use as much available light as possible when filming.

This is probably a stupid question, but how do I know when I've pushed my digital footage shot with a Sony a6300 two stops using FCPX's built in color correction tool?

Winston A. Cely
Editor/Owner | Della St. Media, LLC

17" MacBook Pro | 2.3 GHz Intel Core i7
4 GB RAM | Final Cut Studio 3 | FCPX | Motion 5 | Compressor 4

"If you can talk brilliantly enough about a subject, you can create the consoling illusion it has been mastered." - Stanley Kubrick


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Jeff Kirkland
Re: "Pushed two stops"
on Sep 24, 2017 at 6:24:58 am
Last Edited By Jeff Kirkland on Sep 24, 2017 at 6:30:00 am

You can’t work in stops in FCPX. Most NLEs work in IRE which is based on signal voltage and there’s no simple direct correlation between the IRE percentage and stops of light.

Having said that, Magic Bullet Looks calculates its exposure in stops, not sure about their Colorista plugin though. You could also use something like LUTCalc, which works in stops, to create a LUT that adds an extra 2 stops of brightness to your image.

Otherwise it’s a case of using your eyeballs and stopping when it looks right on the screen.

Plus it’s a technique that’s relates to film but doesn’t really translate to digital shooting. It’s the equivalent of under exposing your footage by two stops then bringing it back up in post, which in a digital world will lead to noisy footage.

----
Jeff Kirkland | Video Producer & Cinematographer
Hobart, Tasmania | Twitter: @jeffkirkland


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Winston A. Cely
Re: "Pushed two stops"
on Sep 24, 2017 at 11:22:22 am

Thank you for clearing my head! I was worried about the digital noise that would occur, too. Digital noise is pretty ugly compared to film grain, especially if you're doing some exposure tricks in post.

Winston A. Cely
Editor/Owner | Della St. Media, LLC

17" MacBook Pro | 2.3 GHz Intel Core i7
4 GB RAM | Final Cut Studio 3 | FCPX | Motion 5 | Compressor 4

"If you can talk brilliantly enough about a subject, you can create the consoling illusion it has been mastered." - Stanley Kubrick


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Mark Smith
Re: "Pushed two stops"
on Sep 24, 2017 at 12:34:02 pm

Pushing in film is basically using gain in digital. THe results of pushing or using gain either add film grain in film or noise in digital. In film choosing to ‘push’ could be a creative choice - like wanting a grainier look over all- adding texture to the image or it could be a practical choice, to compensate for lack of light for adequate exposure.
If you have an object in your frame that is for instance some papers on a table that reads 50 ire on the wfm and you add some gain so that the papers read 70 ire that might be about 2 stops. What gets tricky judging ‘stops’ in the digital world is that there is also manipulations that can be done to gamma curves that make the judgement of stops more difficult. Shoot a test with your camera. Using the picture profile you shoot with normally, shoot a white card at 50 ire, then open the lens 2 stops from your 50 ire setting and record the same card. Bring footage into NLE and check out what the IRE difference is between the 2 exposures. THat will at the very least give you what the camera& lens combo in use thinks 2 stops is. Be forwarned that camera picture profiles can distort results especally ones with strong knee curves at the top of the exposure range ( canon eos profile - I’m looking at you) so choose a flatter profile if possible .


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Winston A. Cely
Re: "Pushed two stops"
on Sep 24, 2017 at 8:57:21 pm

Mark, I hope you don't mind, but I'm going to use this as a daily lesson for my students! What a great, simple way to visually teach my students (and myself!) about what happens when you "push" your digital footage.

Winston A. Cely
Editor/Owner | Della St. Media, LLC

17" MacBook Pro | 2.3 GHz Intel Core i7
4 GB RAM | Final Cut Studio 3 | FCPX | Motion 5 | Compressor 4

"If you can talk brilliantly enough about a subject, you can create the consoling illusion it has been mastered." - Stanley Kubrick


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Mark Smith
Re: "Pushed two stops"
on Sep 24, 2017 at 11:03:57 pm

If you can turn off “knee’ in your picture profile , that would be best. The knee shouldn’t affect moving white from 50 IRE up 2 stops but not being familiar with your camera i say this as a word of caution. If you do this exercise and see what the optical/sensor path thinks 2 stop is in terms of level change, then you can duplicate that inside your NLE and with grading controls and have a direct comaprison of results. Happy to be of service,


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Claude Lyneis
Re: "Pushed two stops"
on Sep 25, 2017 at 4:39:17 am

On many video cameras, setting the gain is often done in db's . In this case a change of gain of 6 db, results in 1 stop, (a factor of 2 in light intensity). So 18 db is equivalent to three stops. If you are using a dslr, gain is expressed in ISO and going from 200 to 400 ISO is equivalent to one stop or a factor of 2 in light intensity. Then there is the question of how to equate the sensitivity of a video camera in terms of ISO, that is yet another adventure.

I need to read some more on what the IRE curve means in terms of light exposure.


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Winston A. Cely
Re: "Pushed two stops"
on Sep 25, 2017 at 11:58:12 am

We are using Sony's mirrorless a 6300's. I really appreciated the low-light level sensitivity of these cameras, without the introduction of distracting digital noise, with the added benefit of being in our price range.

I'm going to look into the specifics on this camera with the above tips and how-to's and run our own tests.

Thank you to everyone for responding. Love learning new things about my cameras because it's more that I can teach my students.

Winston A. Cely
Editor/Owner | Della St. Media, LLC

17" MacBook Pro | 2.3 GHz Intel Core i7
4 GB RAM | Final Cut Studio 3 | FCPX | Motion 5 | Compressor 4

"If you can talk brilliantly enough about a subject, you can create the consoling illusion it has been mastered." - Stanley Kubrick


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Mark Smith
Re: "Pushed two stops"
on Sep 25, 2017 at 3:21:59 pm

Using the gain method of 'push 2 stops' is also valid in terms of getting an idea of what the shift in levels will be though i have slightly less trust in this method than the optical/ sensor method. One thing the gain method does is it shows you directly what the noise penalty might be for a 2 stop push. So start at your base iso, maybe its 800, then bump up to 1600, then 3200 keeping f stop and lighting the same. You may discover some differences in the image depending on whether its pushed in post or in camera with gain.


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Bill Fiebig
Re: "Pushed two stops"
on Oct 11, 2017 at 1:03:46 pm

Regarding the A6300, as I recall, those cameras have a decent dynamic range. By any chance, are you using a light meter? Sekonic has a light meter (478 and 858) that will do cinema as well as conventional photographic light metering. You should be able to accurately gauge the lighting of your projects, and can dial in exactly what you are looking for in terms of pushing the lighting. It may give you more consistent results to film at the desired lighting levels instead of adding in post.


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Mark Smith
Re: "Pushed two stops"
on Oct 12, 2017 at 12:30:36 pm

Keep in mind that camera profiles are the enemy of light meters. If you try to use a light meter with say a canon C300 and EOS profile you’ll eventually find some meter reading that you can relate to exposure and image, but the exposure to image relationship will be very different if you used the same camera and a neutral profile.
Frequently you need to make some adjustments between meter iso setting & camera iso setting to get some agreement and consistency. So if your camera is set to 800 ISO and so is your meter but the image seems underexposed , you may have to set your meter to a lower ISO, like 640, 500 or 400 which means you’ll add more light to your scene to get the exposure result you want with the camera.


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Winston A. Cely
Re: "Pushed two stops"
on Oct 12, 2017 at 7:23:28 pm

Thanks Mark. I do not have one, as my last Sekonic light meter died on me. I have added that to my list of items I need and will get one to test this out. Thanks!

Winston A. Cely
Editor/Owner | Della St. Media, LLC

17" MacBook Pro | 2.3 GHz Intel Core i7
4 GB RAM | Final Cut Studio 3 | FCPX | Motion 5 | Compressor 4

"If you can talk brilliantly enough about a subject, you can create the consoling illusion it has been mastered." - Stanley Kubrick


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Jeff Kirkland
Re: "Pushed two stops"
on Oct 12, 2017 at 9:06:13 pm

You generally calibrate your light meter to the both camera and the profile you are using. If you change profiles, recalibrate.

----
Jeff Kirkland | Video Producer & Cinematographer
Hobart, Tasmania | Twitter: @jeffkirkland


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