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Book lighting, order of diffusion and CTO


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#1 Mathew Collins

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Posted 20 August 2016 - 12:28 PM

Hi,

 

I have observed a commercial shooting from some distance.

 

A DP did lighting like this.

1. 6K Arri PAR

2. Put 2 layer of diffusion. I think 216-Full White Diffusion and 410-Opal. Not sure about the order in which they placed the diffusion frames in front of the source.

3. CTO in front of the diffusion

4. Bounced the light coming from diffusion (could be using silk/Muslin/Griffolyn for bouncing)

 

Would it be called Book lighting?

 

What difference would it make if the light passes thru CTO first and then thru diffusion?

 

What difference would it make if the light passes thru 410 first and then thru 216 or vice-versa?

 

Could someone share their views?


Edited by Mathew Collins, 20 August 2016 - 12:29 PM.

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#2 David Mullen ASC

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Posted 20 August 2016 - 03:32 PM

Not really a book light if they were just bouncing a diffused source - a book light involves diffusing a bounced source.  Doesn't matter what order the color or diffusion is as long as the colored light isn't being bounced back through the same color frame, thus double-gelling the color.  Most people put the color closer to the light than the diffusion to reduce some of the gel kick onto the scene since normally colored gel is shinier than diffusion. 

 

If the end result was what the DP wanted, then it worked, there is no right or wrong way to do something unless it is not really doing anything or is less efficient than some other order of events.

 

But you have to understand that sometimes these things happen one at a time, you do the rig, looks at the results, and then decide it can stand to have another layer of diffusion or something.  It evolved, it wasn't thought-out completely from the start.


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#3 Mathew Collins

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Posted 20 August 2016 - 09:06 PM

Thank you.

 

What are the differences in the light output between bouncing a diffused source and diffused source?

 

Would the the first method make the light softer than the second?


Edited by Mathew Collins, 20 August 2016 - 09:08 PM.

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#4 Robin R Probyn

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Posted 20 August 2016 - 10:35 PM

AFAIK.. the idea of a book light is to bounce a light into a diffusion frame.. the idea being to "evenly fill" the diffusion frame ,i.e. avoid any hot spot in the diff frame.. giving max diffusion of the original light source ..

 

The exact same "softness" can be achieved ,given the space.. by being able to back your source light off to totally "fill" the diff frame..

 

A book light is not intrinsically making the light softer.. although much loved in music /commercials, as it looks good in front of the clients/young directors  ..  :)..  or if you dont have the space to back off your source and getting a big hot spot on your diff frame..

 

The only way to make the light softer is to make it bigger in relation to the subject.. either by moving it closer or having a bigger source and frame in the same place..  just a law of physics ..   a huge light source will still be a hard light if its far from the subject.. i.e. us and the sun..  on a clear day..


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#5 David Mullen ASC

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Posted 20 August 2016 - 11:23 PM

The softness of a light is determined by the SIZE of the source (the source in this case is the bounce or diffusion frame, not the light hitting them) relative to the SIZE of the subject, which is affected by the distance to the subject.  That's it.  A bounced light or a diffused light isn't inherently softer or harder compared to each other, it's all about how large an area of soft light they create, and ideally how even that light is from edge to edge. So if you bounce a light off of shiny white board and get a hard kick off of it, or you spot the light into the center of the bounce surface, you won't get as soft a light coming from that bounce compared to a flatter, more even light hitting a matte white surface where the light fills the bounce surface evenly.  Same goes for shining a light through a diffusion frame, the softness is determined by the size of the diffusion frame and how evenly the light fills that frame with no hot spots, no unevenness of brightness, etc.

 

When I mean by the softness is determined by the size relative to the size of the subject, or the subject's distance to the soft source, is that if you are the subject and from your perspective, a 6'x6' soft light takes up the same size in your field of vision as a 12'x12' soft light that is twice as far away does, then the softness of the light would be the same in both cases, the only difference would be the speed of the fall-off in exposure -- if the soft light is much closer to the subject, then it falls off in intensity much more quickly as the subject moves away from the light compared to a larger but farther soft light, where if the subject moves a little closer or farther towards the soft light, there would be a milder change in exposure.

 

So in theory, once you evenly fill a soft source, bounce or diffusion, from corner to corner, the light cannot get any softer.  If you fill a 6'x6' frame of Full Grid Cloth evenly from corner to corner with no hot spots, then the light won't get any softer if you doubled the thickness of the Full Grid Cloth because the size is determining the softness.

 

What a book light does is allow you to fill a diffusion frame more evenly by using a bounced light to fill it, and you therefore get as much softness as is possible by filling the diffusion frame as much as possible with no hot spots.

 

Now in practical reality, some people might find it easier to fill a soft white beadboard as a bounce than shining a light through a diffusion frame, depending on the material.

 

Sometimes which way you go is a space issue, do you have more room for the light that hits the card or diffusion from behind or in front?

 

Also, soft light is not some monolithic effect, if it is not a theoretically perfect and evenly bounced light or evenly-filled diffusion frame, it will have some hardness or texture depending on the nature of the inefficiency.  For example, let's say you use a silk as a diffusion.  It spreads the light in a sort of X-shape pattern instead of a circular glow.  The weave of the fabric may also be loose enough that besides spreading the light, it also allows some sharp light to leak through the holes in the fabric, creating a soft source with a fainter hard source mixed in.  If you bounce a light off of a shinier surface, you may get a hot kick that also creates a fainter hard light in the center of a larger soft light.  Some people like these effects, the faint hard light mixed into the soft light can create some feeling of sharpness, some interesting specular kicks off of reflective objects, etc.


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#6 Mathew Collins

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Posted 21 August 2016 - 12:37 PM

Thank you David, Robin.


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#7 Robin R Probyn

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Posted 21 August 2016 - 07:51 PM

I was once shown an interesting way to show this law of physic,s... hold one finger of one hand about 3 inches away from the palm of your other hand.. and then move the two in unison towards and away from any light source .. and notice the shadow of the finger on the palm of the other hand..  


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