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The size of a mirror used for redirecting light

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#1 Tom Yanowitz

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Posted 27 November 2016 - 11:03 AM

Hello,

I haven't had a chance to use mirrors on sets yet.

My question is : if your goal is to reflect a light source onto the subject, to extend the virtual source to subject distance for fall-off reasons, or for any other reasons,

how does the area of the mirror influence the lighting ? especially for Fresnels, or any relatively small and harsh sources ?

 

Unrelated PS : David Mullen, please come and show The Love Witch in France, I want to see that film !!


Edited by Tom Yanowitz, 27 November 2016 - 11:03 AM.

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#2 David Mullen ASC

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Posted 27 November 2016 - 12:10 PM

The mirror itself will crop/cut the light so it has to be big enough so that you don't see its borders on the pattern it throws, unless that is OK for the shot.  In other words a 4'x4' mirror board, for example, will throw a square-ish light pattern from reflecting the hard source, but the pattern is usually large enough for most purposes.  The closer the mirror is to the light, the larger the pattern will be but the less you are extending its throw compared to shining the light directly.  In other words, you could have a smaller mirror right next to the light that would throw a larger pattern but would hardly add to the distance that the light is traveling.  The spread of the pattern is determined by the size of the mirror, which is cropping the original source.


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#3 Tyler Purcell

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Posted 27 November 2016 - 12:57 PM

The mirror trick is one that I pull out when I've got a big room to light with only one or two sources. The way I use it, enables the room to seem well lit from multiple sources, without taking the time to do so. It does require some sort of high power light, a 2k tungsten would work for locations with no windows. If there are windows, I'll use bigger HMI's and simply color balance for outdoor light.

Since I'm always working with little to no money, I go to a local 99 cent store and buy the cheapest flexible tall mirrors (they aren't made of glass). We then attach them to C stands or combo light stands by drilling holes in the top and bottom and using a ratcheting clamp bracket with a pin you buy from home depot. This way you can bend the mirror, lock it in place and get light refraction instead of simply reflection. We'll then use gel covered flags to tint the refracted light and it looks amazing.

The great thing with the smallish mirrors is that all the light that passes by one mirror, can be reflected by another. So we'll literally have a bunch of these mirrors in one place in a given room, all reflecting to a different location, with gels, gobo's and sometimes other smaller mirror devices helping to spread out the beam.

When you're dealing with actors key light, you've gotta bend the mirror so the middle is concave. This makes a stronger beam of light right in the center of the mirror. Then all you've gotta do is put a silk inline with the actors to diffuse the harshness of the light. This is the tricky part because you want the silk as close to the actors as you can get it and I've found throwing a tiny bit of very light orange gel (I buy the stuff in full rolls) over the silk, warms it up just enough to get good face tones with this setup.

The only downside to mirrors is the time it takes to get it right. You really need a crew who has worked with them before to understand light refraction vs reflection. I've had gaffers scratch their heads and wasted time on set setting this rig up for them. In the long run, the look is fantastic, but it's VERY time consuming.
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#4 John E Clark

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Posted 28 November 2016 - 01:01 PM

The only downside to mirrors is the time it takes to get it right. You really need a crew who has worked with them before to understand light refraction vs reflection. I've had gaffers scratch their heads and wasted time on set setting this rig up for them. In the long run, the look is fantastic, but it's VERY time consuming.

 

What do you mean by 'refraction vs  reflection'?

 

Refraction -- the change in direction when light passes from one medium to another, most commonly seen in for example a stick half in water, half out, and it appears to be 'broken' at the water's surface. Refraction also figures in lens designs as different types of glass or other materials have different refraction indices.

 

There is a small amount of 'refraction' if the mirror has a thickness of glass and the reflective surface is on the opposite side of the glass from the incident light. But if the surface of the mirror is the reflective surface, there would be no 'refraction'.

 

Of course creating a concave reflective surface will 'focus' the incident light.


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#5 David Mullen ASC

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Posted 28 November 2016 - 01:24 PM

The original question was primarily about using a mirror to increase the distance between the hard source and the subject in order to decrease the rate of fall-off and to increase sharpness, not so much about using mirrors to make one source into multiple sources or for passing the light through diffusion once it reaches the subject.

 

One problem with mirrors is that they can jiggle and shake, which cause the light pattern to also move around.

 

I've used them on the underside of the eaves of a house outside of a window or up against a ceiling in order have a beam of light come back down at a steeper angle than would be possible.


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#6 Michael LaVoie

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Posted 28 November 2016 - 01:50 PM

A fun mirror trick is to stripe the face of it with clear packaging tape and then gently and randomly crack it from behind.  Shining a light into it will then produce a broken up pattern of light similar to using a cookie.  


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#7 Stuart Brereton

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Posted 02 December 2016 - 12:07 AM

The mirror trick is one that I pull out when I've got a big room to light with only one or two sources. The way I use it, enables the room to seem well lit from multiple sources, without taking the time to do so. It does require some sort of high power light, a 2k tungsten would work for locations with no windows. If there are windows, I'll use bigger HMI's and simply color balance for outdoor light.

Since I'm always working with little to no money, I go to a local 99 cent store and buy the cheapest flexible tall mirrors (they aren't made of glass). We then attach them to C stands or combo light stands by drilling holes in the top and bottom and using a ratcheting clamp bracket with a pin you buy from home depot. This way you can bend the mirror, lock it in place and get light refraction instead of simply reflection. We'll then use gel covered flags to tint the refracted light and it looks amazing.

The great thing with the smallish mirrors is that all the light that passes by one mirror, can be reflected by another. So we'll literally have a bunch of these mirrors in one place in a given room, all reflecting to a different location, with gels, gobo's and sometimes other smaller mirror devices helping to spread out the beam.

When you're dealing with actors key light, you've gotta bend the mirror so the middle is concave. This makes a stronger beam of light right in the center of the mirror. Then all you've gotta do is put a silk inline with the actors to diffuse the harshness of the light. This is the tricky part because you want the silk as close to the actors as you can get it and I've found throwing a tiny bit of very light orange gel (I buy the stuff in full rolls) over the silk, warms it up just enough to get good face tones with this setup.

The only downside to mirrors is the time it takes to get it right. You really need a crew who has worked with them before to understand light refraction vs reflection. I've had gaffers scratch their heads and wasted time on set setting this rig up for them. In the long run, the look is fantastic, but it's VERY time consuming.

As John Clark pointed out, refraction is when light changes direction as it passes from one medium to another. A cheap plastic front surface mirror is not refracting light at all, but rather focusing it as it is bent, rather like the reflector in a lamp. A 'gel covered flag' wouldn't transmit any light at all, as a flag is designed to cut light entirely.

 

Having all your mirrors 'in one place in a given room' is unlikely to yield a useful result, anymore than lighting a room from one position would with movie lamps.

 

If you have examples of rooms lit with this technique, Tyler, perhaps you can share them.


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#8 Tyler Purcell

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Posted 02 December 2016 - 01:23 AM

Sorry for the confusion...

Gel covered flag FRAMES. I missed the word "frame", sorry that confused you.

I always thought bent light was "refracted" light. I gather that's not completely accurate.

When you put mirrors together, in front of a beam of light, you are able to reflect that light into different parts of a given room. Thus, allowing for quicker setup's and one light generally covering more of a given space, with a distinctly creative look.

I will post some examples of this in a bit.
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#9 Stuart Brereton

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Posted 03 December 2016 - 09:30 PM

Please do.


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#10 Robin R Probyn

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Posted 04 December 2016 - 08:16 AM

Mirror Mirror on the set..

You need the sun ,let us not forget

Should that bright orb cease to emit,the production is truly in the s h i t

Refraction or reflection.. the DOP will be on a homeward bound direction


Edited by Robin R Probyn, 04 December 2016 - 08:28 AM.

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#11 JD Hartman

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Posted 04 December 2016 - 11:10 AM

Sorry for the confusion...

Gel covered flag FRAMES. I missed the word "frame", sorry that confused you.

I always thought bent light was "refracted" light. I gather that's not completely accurate.

When you put mirrors together, in front of a beam of light, you are able to reflect that light into different parts of a given room. Thus, allowing for quicker setup's and one light generally covering more of a given space, with a distinctly creative look.

I will post some examples of this in a bit.

 

But the light rays are not bent Tyler, just reflected.  Angle of incidence equals angle of reflection, no bending or refracting of the light rays as a prism would do.  Just a matter of terminology.


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#12 Igor Trajkovski

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Posted 04 December 2016 - 05:24 PM

The idea of using mirrors or nearly-mirror-like materials to direct one light source,

for the purpose of generating multiple light sources and/or reducing fall off, was

utilized by DoP Christian Berger in the "Cine Reflect Lighting System".

I've posted in another thread once about it, including links
to videos describing the usage, the system, setups and so on,
but it somehow passed unnoticed/uncommented... :)

Here link to that post if anyone interested:

Cine Reflect Lighting System
 

 

Best

 

Igor
 


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#13 Stuart Brereton

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Posted 04 December 2016 - 06:51 PM

I've seen this system before. While it obviously has its uses, it still suffers from the fact that all the light is essentially coming from the same place.


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#14 David Mullen ASC

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Posted 04 December 2016 - 07:31 PM

It's fine when it's the most efficient way to achieve something, then it becomes too clever by half when it isn't.


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#15 Tom Yanowitz

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Posted 05 December 2016 - 06:28 AM

Thanks for your answers ! And also the semi-unrelated discussion that followed, which is interesting as well.


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#16 andrew ward

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Posted 11 December 2016 - 09:55 AM

Tyler P;
Thats a weird system but I dig it.

Are you talking cheap plastic mirrors like bits of thin film? So you can bend them? Or plastic solid ones ans you only bend them a little?

And you mean like a magic arm?

This sounds like a really weird way to do things and I would have thought its just a way to send weird blotches of light aroun a room, but like I said im into it!
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#17 andrew ward

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Posted 11 December 2016 - 09:57 AM

Reading it again I think youre just bending the mirrors on one plane. I thought you were twisting them as well.

Why bend/flood them? Why not just bounce a square shape?
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#18 Tyler Purcell

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Posted 11 December 2016 - 05:04 PM

All I know is that my gaffer goes to the 99 cent store and comes back with these cheap Chinese mirrors that aren't made of glass.

He drills holes in the top and bottom to attach clamps that he gets at home dept. They're like clamshell speed rail clamps, but they're adjustable and have a metal screw end for mounting. This way, he can use a C stand or combo stand as the way to mount them.

The point is that you can take ONE SOURCE of light and simply move the mirrors around to create the look. Bending the mirrors focuses intensity or disperses it, usually in a pretty cool pattern, which is more akin to light hitting a window and reflecting off things like a shade. Square shapes are great for a key but they aren't great for lighting the background. I personally like using diffusion as my key source, so one mirror will head towards that diffusion and the other one's will simply fill in the room. Rob went so far as to hang mirrors behind people and bounce light back towards them. I never went THAT far, favoring a single tungsten as backlight vs another mirror. It already takes up a lot of time to setup the mirrors, trying to get another run out of them is hard, it just takes a bigger crew then I've ever had. For the background, I'll usually have the gaffer put a gobo or filtration of some kind on the outgoing side of the mirror, so we can manufacture a look.

I don't remember trying to twist the mirrors, but when I was a kid, I learned this trick from Rob Hahn (thanks to an AC article). He used it on a few films including 'The Score' and I really liked it. So I practiced it for quite a while, using it in several fun projects, though nothing really commercial until I moved to LA. My first feature as a cinematographer 'Sweet Potato Pie' was the first time I used it on a real movie. We rented an 18k HMI, put it outside of the house we were shooting at and used mirrors to bounce the light around instead of putting lights inside the house. The critical part was being able to create cool patterns in big rooms. I used it again on the producers next film 'Out on Parole' but the producers and I had a falling out (didn't pay the agreed amount) and I haven't been able to find a copy of either movie.

It's been 12 years since I made those two features and since then, I haven't really needed to use this trick. The short film I just finished, is literally the first time I've worked on a fully budgeted narrative project in a decade (I've been shooting documentaries, industrials and commercials). I'm crossing my fingers that in 2017 I'll be on a big enough shoot where we have the time to use this trick and I can make a little video on how it works. I'm just so busy, I simply don't have the time to produce a product that's worth while. I will put it on the list to do though because it's a great trick to have in your bag of tricks.
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#19 andrew ward

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Posted 12 December 2016 - 08:35 PM

Thanks!

I LOVE it.

Ima do it!
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#20 Mathew Collins

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Posted 06 January 2017 - 09:24 AM

The original question was primarily about using a mirror to increase the distance between the hard source and the subject in order to decrease the rate of fall-off and to increase sharpness, not so much about using mirrors to make one source into multiple sources or for passing the light through diffusion once it reaches the subject.

 

One problem with mirrors is that they can jiggle and shake, which cause the light pattern to also move around.

 

I've used them on the underside of the eaves of a house outside of a window or up against a ceiling in order have a beam of light come back down at a steeper angle than would be possible.

 

>increase the distance between the hard source and the subject

 

David, how would mirror increase the distance between hard source and the subject? My understanding was mirror would become the new virtual source.


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