Light Ratios

[Gavin Seim]

Light Ratios:

They represent difference between highlights and the shadows in a scene. It's amazing how many images are being made flat these days. Understanding simple ratios tells you a lot about your scene. It helps you control depth and shape and shadow. It helps you visualize and make an image work your way.

Lets imagine a face in a portrait, whether strobe lit or natural lit. Lets say you meter and light on the shadow side reads 1 stop darker than it does on the highlight side (you can even measure this with your in camera spot meter). This means double the light is reaching the highlight side, or a 2:1 ratio.

Anytime you increase or decrease by a stop, you double your light and thus your ratio.

A few highlight/shadow ratio examples…

1 stop diff = 2:1
1½ stop diff = 3:1
2 stop diff = 4:1
3 stop diff = 8:1

Now I certainly don't claim to be the grand master of ratios, I'm studying them further all the time. But at their core they are another simple powerful way for us to better work with and understand our light. We'll be looking at them further during my EXposed series... http://seimeffects.com/exposed

There's certainly more to discuss on this topic. Lets do it...

[TSSP]

I've done a few lighting workshops and taken on assistants who only wanted to learn about lighting, as soon as you mention things like lighting ratios, logarithmic functions of light, inverse square law... et all things math and light related I always enjoy seeing the blank look on faces as their minds puddle into goo. :-p

I think the hardest part in relating the nature of light using mathematical terms is getting some one to correlate the sets of numbers (in the case of ratios) with what things actually look like.  It is ESSENTIAL, if some ones intention is to best understand the medium, to know how these abstract concepts relate back to the actual photograph.  One of the best ways of doing that is shoot and experiment, review your results thoughtfully and adjust your approach for next time. Second to that, look at another persons work, ex: like in this video by the late Dean Collins http://www.youtube.com/watch?v=JyzkWxtKWm8 recording of a lecture from Brooks Institute. 

These things should be scary or unapproachable because they are the stock and trade, the literal tools with which photographs are made.

Hope the video link helps- Collins has a great stage presence for lectures and was a great resource of knowledge.  You can find more video clips from his lectures on youtube or out on the net.

All the best-

[Gavin Seim]

Very true. Without an understanding of how the math will effect our image you have only numbers. And hence, visualization is critical.

Great video too. Marking that one.