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Keeping the underexposure within 7219 lattitude


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So, my very first post here at cinematography.com. I am sorry if this has been asked before, but in part with English not being my first language I have not been able to formulate this question probably in seaches and thus come up empty handed. 

So this quesion is in two parts, a theoretical question about lattitude of Vision3 and a practical question of how to keep shadows within the range of same lattitude.

So in two days i will be shooting a very low budget proof of concept with a scene in a basement. We are limited with lights (2, 2k blondes, 3 800w redheads and one aputure with silks, unbleached muslin and flags to boot). I will be shooting on a 416, ultra primes and 500T 7219. I am however pushing it 1 stop to 1000 asa. In part, because of my success with doing the same in still photography and in part because i simply want to able to expose my characters key at a correct exposure with our limited budget. The film will be scanned as a 2k DPX with a scanity (My only option).

So, about the dynamic range (or perhaps lattitude of 16 mm). I have read that Vision3 has 14 stops of dynamic range. David Mullen wrote in a reply in another thread that you could discount the lowest stop since its very close to fog level. Since this seem quite logical i will do the same and discount the lowest stop. 

I will expose with a spotmeter and a greycard. I will expose my characters key at the given value. So, if I exposed the scene at the greycard value for my characters key, how many stops below that can the shadows be without hitting the fog level? 

This math is a little confusing for me, and i guess i just need a good old pre-digital book, but if I exposed at middle grey in a 14 dynamic range. Would it then be correct to assume that i would have 6 stops below and 7 stops above my exposure? If i then discount the lowest stop I would then have 5 stops below and therefor 5 stops of possible underexposure.

Is this a correct assumption or have completely misunderstood something? 

A bonus question. Film handles "overexposure" quite well correct? So another way to keep the shadows within range would be to overexpose the key by one stop and then bring down in post if needed yes?

For the practical question. How would I practicaly meassure that the darkest area of the scene are above the fog level?

My approach would be to simply spotmeter the key and then spotmeter the various dark areas in the scene to confirm that they are not more than 5 stops under the key exposure. 

Since spotmeter is the reflected light, this would be the correct way of keeping everything within the lattitude right? 

Thanks for taking your time! 

Best regards

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There are actual DPs here who can give you better and more detailed answers, but have a look at this chart:

Screen-Shot-2019-08-15-at-10-33-13-pm.pn

The middle gray point isn't always exactly between the two extremes.

And you can't lose by overexposing by a stop or two - or more, if you know what you're doing. I would not bother overexposing if you're pushing. You're effectively cancelling one with the other, and causing a mess in your head. 😉

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A few things...

1. A "middle" grey card is not in the center of the optimum exposure range.  At the standard rated ISO exposure, it will be about 1/2 stop below the middle, compared to the "X" crossover on a video greyscale chart.

2. When viewing dynamic range on film vs. a digital camera, the DR refers to areas where detail is visible vs. not visible.  But this does not mean that the quality of detail at the extremes is the same as the quality of detail in the middle of the range.  While detail in the deep shadows can be distinguished, it is very grainy, which is disguised by the compression of the detail in the characteristic curve as rendered on a print.  On the highlight end of the curve, it is not so grainy, but also not so detailed either, and there could be some color shifting.  So, it's best to think of the range of tones that you are capturing as about 6 to 8 stops, with everything above and below as "roll off" into shadows and highlights.  This is especially true in 16mm where you are enlarging the grain of the film much more than on 35mm film.

3. When you "push" the film processing, you are gaining "exposure" in the middle by loosing detail in the shadows.  So, if when you expose normally you would get 2.5 to 3 stops of detail below your grey card exposure, when pushed 1 stop you will get 1.5 to 2 stops of detail below your grey card exposure.  Also when pushing, instead of 3 to 4 or 5stops of usable detail above the grey card, by over development of the negative, you will likely loose a stop there as well.  So, when exposing film for push processing, instead of a perceived DR of 6 to 8 stops, it's more like 5 to 7 stops.

Personally, I feel that push processing 16mm film is a pretty harsh look. And, if you do, I would light and expose the film as if you were limited to 5 1/2 stops. 2.5 stops below the grey card and 3 stops above.

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Thanks alot Bruce! 

1. 
Okay, hmm. I will have to read up on that. My thought would be that if the 18 % grey card was correct lit according to its reflectance, then the skin tones would be lit correctly at their reflectance level. I suppose i will expose them using a good old incident meter instead since i can see that i might have misunderstood exposing by greycard and spotmeter. 

3. 
Okay, jesus! I was not aware of this, though it makes sense! It seems that pushing is more a gamma adjustment than a lift, very good that i found out about this! 

What are the parameters that decide if the underexposure value is 3,4 or 5? If there only are 3 stops of usable underexposure from the grey card value, then it seems if you had a key to fill ratio of 3 stops, it would be hard to darken the background beyond that by more than a stop? For tommorows shoot i only need a certain amount of stops to keep the shadows within. Are you suggesting that 4 is a more reasonable number than my pre concieved 5? 

Thanks for the reply!
 

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Quote

1. 
Okay, hmm. I will have to read up on that. My thought would be that if the 18 % grey card was correct lit according to its reflectance, then the skin tones would be lit correctly at their reflectance level. I suppose i will expose them using a good old incident meter instead since i can see that i might have misunderstood exposing by greycard and spotmeter. 

You are correct that spot metering off the grey card is the same as using an incident meter.

Quote

What are the parameters that decide if the underexposure value is 3,4 or 5? If there only are 3 stops of usable underexposure from the grey card value, then it seems if you had a key to fill ratio of 3 stops, it would be hard to darken the background beyond that by more than a stop? For tommorows shoot i only need a certain amount of stops to keep the shadows within. Are you suggesting that 4 is a more reasonable number than my pre concieved 5? 

Sorry, I don't understand this 😞

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Hello Bruce, 

No, i can see now that i misread your original reply. You wrote that you normally would have 3,4-5 stops above grey card value, where as i read it as 3,4-5 stops of underexposure.

I can see now that you wrote that if you expose normally then you would have 2.5 to 3 stops of underexposure with detail. This number is just surprisingly low to me. Since a key to fill ratio of 3 stops is so common, it would seem impossible in such a situation to darken the background further than a mere stop from the objects fill side. 

Thanks for your replies Bruce, especially with how push processing actually works, i had completely misunderstood it. 

 

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My dynamic range numbers are from my experience and testing shooting film and printing on film.  With a digital scan and color correction, you will have some more latitude, but not so much in the shadows before the film grain starts to become too obvious.  This is especially true with 16mm vs 35mm film.

Since your goal is to shoot 16mm in low light, the shadow side of things is far more important than the highlights. And push processing the film will not gain you any shadow density on the negative.

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On 8/16/2019 at 1:35 AM, Bruce Greene said:

Personally, I feel that push processing 16mm film is a pretty harsh look. And, if you do, I would light and expose the film as if you were limited to 5 1/2 stops. 2.5 stops below the grey card and 3 stops above.

I have seen scans of 7219 pushed by a stop. It looks great. I can't show them because they were taken offline, unfortunately.

However, have a look at this video of 2-perf 5219 pushed by two stops. Note that the owner has also made an HQ version (2.4GB) available for download:

 

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