MadSci Network: Computer Science
Query:

Re: How does a Professional Cameraman use Light?

Date: Fri Feb 28 15:08:42 2003
Posted By: Gareth Evans, Industrial R&D practitioner and manager ( retired )
Area of science: Computer Science
ID: 1046210840.Cs
Message:

Question:	How does a Professional Cameraman use Light?

Response:	Laura, thanks for your question.  Many of the ways 
photographers use light are of course for artistic reasons.  Iíll touch on 
that area but I assume since you used the Madsci site, you want some 
technical information.

You mention professional photographers particularly.  One of the 
differences between a professional and an amateur photographer is that 
the 
pro is likely to spend a lot more money on equipment including lighting.  
They can therefore have more control over how a subject is illuminated 
or ďlitĒ .  The reasons for wanting this control apply to any 
photographers though the amateur may be less skillful and 
knowledgeable.  

One of the main reasons for changing the lighting of a scene is because 
of 
a basic difficulty of reproducing a scene on paper.  Every scene has a 
range of brightness in it.  For example, a scene including a man in a 
white shirt and black suit in bright sunshine will have a large range of 
brightness.  The brightest area, part of his shirt may be over a  1000 
times brighter than the darkest area, part of his suit, perhaps in a 
shadow.  A negative film and some of the best digital cameras can 
respond 
to the light in the scene even when the brightness range is this large.  
The difficulty comes when printing the image on paper.  When you view 
the 
image, reflections and scattering of the light all around you from even 
the darkest parts of the printed image means that the darkest parts are 
never as dark compared to the brightest parts as the original.  The range 
of brightness in a print normally experienced by the viewer is less than 
100 to 1 that is less than a tenth of the original scene in this case.

Itís not as bad as it seems since we are sensitive to ratios of light 
intensity or brightness.  In the example Iíve used this means that we 
sense only about 60% of the brightness range.  What happens to the rest 
?  
We experience this loss by not being able to see detail in shadows which 
appear as areas of uniform black or highlights, where we just see uniform 
white.  Often a picture will have both defects so we wonít see any texture 
or shape to the affected areas.  

So thatís the problem.  Now, what can we do about it ?  There is not much 
the designers of films and papers can do about this.  I know, because I 
used to try when I worked for Kodak !  We made progress making blacks 
blacker and whites whiter to extend the reproduced brightness range but 
the laws of physics are hard to beat !  Professional materials are also 
designed differently to reduce the extent of this shortcoming of the 
system.  

The professional photographer with his extra control over lighting can 
help a great deal, especially in a studio.  Subjects can be lit to reduce 
the brightness range so that little or no detail is lost in the 
reproduction.  They do this by having several light sources in different 
positions.  Often they use diffuse lighting, that is lighting which uses 
some means of talking light from a lamp and spreading it, for example by 
using a white screen between the lamp and the subject which is then 
illuminated by the whole screen area.

Another whole are of photography is concerned with filters and devices 
which modify the light entering the camera.  Coloured filters can of 
course change the colour of the scene and these can be used in front of 
lights or camera lenses.  Other filters can soften the focus, retaining a 
lot of sharpness but losing some distracting detail.  These can be useful 
with portraits by producing flattering results.

 So what about the poor amateur?  Well there are some things we can do 
to 
help make photos better without much money.  For example ďfill-in flash is 
a great way to reduce the brightness range for back-lit subjects.  
Sometimes you can take a picture of someone with a bright background, 
perhaps in a room with a big window behind.  The result is often almost 
like a silhouette with no detail of the main subject, the people.  Using a 
flash even though there seems to be lots of light will help expose the 
important part of the scene enough to give a pleasing result.  You are 
using professional techniques of using light to reduce the brightness 
range.  

Best of luck with your project. 




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