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Eric Gesualdo

Perks to sticking with tungsten when shooting digital?

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6 hours ago, Brian Doran said:

I'm not sure that this logic holds up. Peak photopic sensitivity is defined as being 555nm, which is a green color. Check out this luminous efficacy chart. Maybe I'm misreading, but it also feels like you are referring to blue light as being longer in wavelength, while the inverse is true. If anything, our scotopic vision is more sensitive to blue light than our photopic. Please let me know if I'm misinterpreting your post.

Ah you're right--I mistyped, meant shorter of course. I'll edit my post so as not to cause future confusion. Scoptopic vs photopic, that's kind of what I meant to say--if we light scenes in darker conditions (and most people also view content in darker conditions) than we'll perceive a bluer light better than warmer light (it's not peak sensitivity, but it's closer than red.)

52 minutes ago, David Mullen ASC said:

"Emotionally" a single candle flame is a "soft" source but in practical lighting terms, it is a fairly sharp source depending on the size of the flame.

I actually think this illustrates what James is saying here. When I think of, say, Barry Lyndon, I don't think of that movie as being lit by hard sources--in my mind it feels very "soft." But obviously when you actually look at stills the candlelight scenes are actually quite hard.

That said, I think it's a human perception flaw and likely shouldn't be something that is relied upon.

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5 hours ago, David Mullen ASC said:

When I use a Litemat 8 on a face, the last thing I think of is "crisp and sharp" to describe the effect. And when I light the face with a direct tungsten Source-4 Leko spot, "soft" is also the last thing that comes to mind.

I have to ask, what is the definition of hard and soft for light then? Wouldn't it be how sharp or blurred a shadow patten it creates?

No. I am not using the terms hard and soft in relation to shadow patterns. Characteristics like falloff and it's behavior upon striking a surface are part of what I'm referring to.

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29 minutes ago, James Compton said:

No. I am not using the terms hard and soft in relation to shadow patterns. Characteristics like falloff and it's behavior upon striking a surface are part of what I'm referring to.

Are you referring to the rate of falloff here? 

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Posted (edited)
3 hours ago, James Compton said:

No. I am not using the terms hard and soft in relation to shadow patterns. Characteristics like falloff and it's behavior upon striking a surface are part of what I'm referring to.

But isn't that the criteria to describe a light .. ? exactly that .. its behaviour when striking a surface.. that why we refer to hard /soft light..  etc.. there has to be some common language to do this job ....   I mean what do you do when your ordering lights .. or discussing with a director the look of a scene..  when you say that a 8 x 8  LED lighting a face is crisp and a 2K open face incandescent , lighting the same face from the same distance ,will be a soft light ?? ..  it must be pretty confusing .. I mean why not just call it what everyone else does  ..

Rate of fall off is the inverse square rule .. nothing mystic about it .. sorry to bang the drum and obviously I have too much time on my hands .. but this is the same as the film vs digital debate .. where film is preferred ,not as just a personal preference ..but as some mystical , religious, undefinable .. undebatable cosmic force ..that makes it "better" for every film and very scene ..and that digital films are all crap due to itheir "binary" nature.. and yes then will come the line, when faced with hard logic. .. "Its organic  " .. or " you don't understand because you think Star Wars is not real " 

Edited by Robin R Probyn

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Posted (edited)

I have found that shooting at 3200K and even lower (household bulbs seem to be more like 2700...2900K) create a lot of noise in the blue channel compared to shooting in daylight. 

Have you done tests where you put a blue filter (like 80C) on the lens and to compensate for the 1 stop loss of light double the ISO?

Will this cause just more noise overall? (of course this depends on the camera and ISO + other factors)

I really need to test this myself at some point,

 

 

Edited by Jan Sandvik

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You're not really helping the noise in the blue channel if you end up pushing the ISO to compensate for the blue filter, you'd basically be increasing the noise in the other two channels to match the noise in the blue channel. If you don't increase the ISO, yes, a blue filter would improve the noise in the blue channel if you compensate for the filter loss. Even a pale blue filter might be enough to help.

Or just use a lower ISO in general and improve the noise in all the channels.

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Thanks, David – your explanation makes sense. I need to experiment with a 82B filter I have buried somewhere,  and compensate by opening the aperture a half stop instead.

But there are special situations that still baffle me: I'm shooting with a Blackmagic Pocket cinema camera 4K which has a dual native ISO feature. I have a gut feeling shooting 1250 ISO (low end of the high ISO range) with a blue filter could result in cleaner images than shooting at 800 ISO (high end of the low ISO range) without a filter. But this is a special case and would need some testing, it also alters how tonal values are distributed.

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Posted (edited)
On 5/29/2020 at 2:29 PM, Robin R Probyn said:

Jon have you been at the Port again .. 🙂 ..  we do know what light is .. very scientifically.. its been studied to death from 100,s of years.. what is this mystery of which you speak..  

How deep do you want to go, Robin 🙂 No, not been at the port.

I was speaking of light in the sense of what we know of it from quantum physics. Yes, cinematographers and people like that know all about what light is, in the sense of dealing with it and what happens when we do this and what happens when we do that, and how it can be measured in all sorts of ways. But I was talking about the stuff of what light actually is. It's a pretty surprising thing, light. It behaves as both wave and particle, and appears to alter what it does according to context. It freaks out those people who like to smugly think we know everything in science. Such an idea is laughable. We know very little. As I said, we live in an arrogant age of science. We have our neat computer models that reassure us that we live in a reasonable world. We don't. The real world is scary and unknown and contemporary man can be uncomfortable with that, because modern man has lost faith in ...... I won't even say it. That's how I see it.

Here is something that might be of interest.

https://blogs.scientificamerican.com/observations/what-does-quantum-theory-actually-tell-us-about-reality/

Edited by Jon O'Brien

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12 minutes ago, Jon O'Brien said:

How deep do you want to go, Robin 🙂 No, not been at the port.

I was speaking of light in the sense of what we know of it from quantum physics. Yes, cinematographers and people like that know all about what light is, in the sense of dealing with it and what happens when we do this and what happens when we do that, and how it can be measured in all sorts of ways. But I was talking about the stuff of what light actually is. It's a pretty surprising thing, light. It behaves as both wave and particle, and appears to alter what it does according to context. It freaks out those people who like to smugly think we know everything in science. Such an idea is laughable. We know very little. As I said, we live in an arrogant age of science. We have our neat computer models that reassure us that we live in a reasonable world. We don't. The real world is scary and unknown and contemporary man can be uncomfortable with that, because modern man has lost faith in ...... I won't even say it. That's how I see it.

Here is something that might be of interest.

https://blogs.scientificamerican.com/observations/what-does-quantum-theory-actually-tell-us-about-reality/

Yes Ive always seen the world as scary and unpredictable .. because of contemporary man , not science itself.. I think science has disproved alot of mumbo jumbo that was used for nefarious purposes over hundreds of years  ..     but lost faith in what .. and what do we actually not know about light .. 

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Feynman's QED is a fantastic introductory book on quantum electrodynamics designed for laypeople. It explains how light actually works, although you might reach the last chapter wishing it didn't.

In all seriousness it does things such as tell you why transparent objects with parabolic profiles (er, lenses) do what they do. Or at least on average do what they do.

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Since you've read the book, tell me -- does a photon actually get slowed down when traveling through a medium or is it just taking longer to get through because it is zigzaging, bouncing around, etc.?

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7 hours ago, David Mullen ASC said:

Since you've read the book, tell me -- does a photon actually get slowed down when traveling through a medium or is it just taking longer to get through because it is zigzaging, bouncing around, etc.?

According to traditional physics the speed of light is constant so it would have to be the route being longer.  Like photons generated in the sun take thousands of years to reach the surface but they are always traveling at the speed of light, they just keep bumping into crap and bouncing around. 

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What happens to light in dielectric medium like glass is interesting and you don't actually have to delve deep into QED to explain the basic phenomena. There's a Ewald-Oseen extinction theorem in wave optics that explains whats' happening.

Briefly put, the light wave doesn't slow down coming from air into the glass. It stubbornly continues to propagate at the same speed for a while. Doing so, it forces the medium's atoms' electrons to oscillate at the same frequency (it's more complicated really, but a crude approximation works at our visible wavelengths) and generate "secondary" waves (and then "tertiary" and so forth since one dipole excites the other) propagating backwards - thus we have a reflected wave - and forwards. Waves from each atom add up with phase shifts - because they were emitted from different points in glass. There in the sum we have a wave just like the incident one but with the opposite sign, so the incident wave is canceled out. The rest, when summed, looks like a wave propagating slower by a factor of refractive index.

And you can view wave optics as "statistics of many photons": while in quantum we're talking about the probability of finding a single photon somewhere, in wave optics we're dealing with an EM wave formed by myriads of photons carrying an energy proportional to their number. Don't take is as legitimate definition though as it's very, very inaccurate. Many concepts (diffraction et cetera) are similar, but they're applied to different objects in QED and classical ED. 

Feynman's books are brilliant by the way, all of them. And used to be very popular on the other side of the curtain too.

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I think Michael puts it very well; what we perceive as the behaviour of light is in fact the average behaviour of a (very) large number of possible photons. Light doesn't actually go in a straight line, it just looks on average as if it does.

The double-slit experiment is hilarious here; in short you can demonstrate wave interference with only one photon present at a time. So what's it interfering with?

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