Jump to content

fall-off


Recommended Posts

  • Premium Member

Is it me, or is it not so much about the change in lighting anyone wants between a wide and a closeup, it's more about the fact that you can't create the lighting in the wide that you'd want for the closeup? You can't have enormous diffusion six inches from someone's earhole then shoot them full length, but if it were possible to create that closeup lighting for the wide, anyone would just do that and get everything they needed.

Link to comment
Share on other sites

  • Premium Member

Sure, what works for a wide shot in a room might not work for a close-up, and you can't get the close-up lighting in the wide shot. On the other hand, wide shots also need to be lit well and work on their own too, they don't just exist as a vehicle for getting into the close-up.  Often I've had a hot slash of light on some shiny furniture that puts a small reflective kick of light onto the actor's face that is only visible in a close-up, so it's not distracting in the wide... but usually I flag it off in the close-up.  Silverware on a table is a classic example, you get in close with the camera and then you notice a spot of light on the cheek or chin, etc. from a reflection.

I think every cinematographer would love to light a wonderful wide master and have that lighting look great on the close-ups as well with no changes. Things would go a lot faster on set and there would be no concern with matching. Sometimes you manage it or get pretty close.  David Watkin was notorious for beautifully lighting a room and not changing things for the coverage unless absolutely necessary. It's not a bad approach by any means, it just means forgoing a certain level of glamorization of the actors.

Link to comment
Share on other sites

https://gabrieldevereux.com/calculator/
 

Here’s how to calculate large near-lambertian (matte) source propagation.

A simplistic view of it - explained crudely for the umpteenth time.

1, 2 or however many light sources can be illuminating the reflector. It is assumed these light sources are at an acute angle to the normal of the reflector and the surface is near lambertian.

The reflectance value of muslin is approximately 95%/0.95. It then models the reflecting soft surface as being composed of many point sources, m*n (the amount of point sources scale with the size of the reflector), whose total light output is the same as the total luminous flux of the original light sources (minus losses) If the total luminous flux of the sheet is L, then the luminous flux of a single point source is L/(m*n).

These point sources emit light isotopically at a solid angle of 2pi steradians (only in front of the surface). The algorithm computes the luminance at some point z on the axis perpendicular (the normal) to the reflector passing through its centre. To this end, it simply needs to find the luminance produced at this point by each point source, apply certain laws such as lamberts cosine, and then sum these values to get the total luminance. 

Note that the number of point sources, m*n, can become arbitrarily large. However, for m*n => 50 the approximation is almost perfect (note there are approximately 7*7 (49) point sources per m**2 so this algorithm is accurate for sources larger than 3’ x 3’). 
 

The rest is basic geometry. 
Fall-off and contrast is not related. Fall-off is a term, I believe, taken from radiometry. A very poignant topic for cinematography.

Contrast in our world is artistically relative. How you interpret the two is up to you but, it’s probably easiest to view the two separately.

Also if you have any questions about the above calculator please do ask. It’s all reasonably simplistic math. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...