Saturday, March 15, 2008

Lighting 102: Unit 2.1 - Apparent Light Size

This is the third lesson of the Lighting102 course on strobist.com and after the first and second exercises it's exciting to see the potential that off camera flash has to offer the photographer.

The third lesson of this course was rather confusing to me. I think I understand the concepts, but my test images from doing the exercise have left me wondering I have indeed fully grasped them.

My understanding of the subject is summed up as follows:
  1. There are three lighting zones that affect how large a light looks; diffused highlights, shadows and the "diffused highlight-to-shadow transfer area",
  2. The "diffused highlight-to-shadow transfer area"is the primary component in defining if a subject is being lit by hard or soft light.
  3. A hard light can look soft and a soft light can look hard depending on the size of the light source to the subject
I think much of my confusion came from not getting the expected results from the images, which came about by the size of the light source to the subject. From the 38 images I took I selected the following eight images to discuss what I discovered about "Apparent Light Size" and also some interesting other discoveries :-)

The first two images were taken from close up the first with a bare light flash with a piece of wax paper diffuser and the second taken with a Stofen filter. The second image shows a wider transition area on the lemon creating a softer light source, however the shadow on the ground looks similar. It is obvious that the Stofen filter really helps to spread the light out and at the same time reduces the intensity.


The next six images were all taken from the same distance - about 6 ft - and the same zoom on the strobe. The only thing that changed was the size of the light source and the strobe power in order to get similarly exposed images.

The first set of images are taken with the bare light and a Stofen filter. The transition area is much more narrower and more harsh from the bare light than the Stofen, which I expected. What was interesting for me was the amount of extra power needed for the Strobe when the Stofen filter was used.

When the light source was much closer to the subject the difference in the amount of power between the bare light and Stofen filter seemed negligible (reflecting upon this makes it obvious now). I had not thought that using the Stofen filter would have made 2 stops difference.


The following two images were taken with umbrellas, one white shoot through and one reflector. I'm not sure if I'm right with my next conclusion, but I'll do some more research later to confirm it. I found that the white shoot through umbrella gave off more light for the same amount of power and distance, whilst the reflector umbrella gave off less light light but produced a larger apparent light. To get the same amount of light from the reflector umbrella I would expect I would need to pump up the power by 1/2 a stop.


The last two images were taken with the bare light bounced of the ceiling and wall. Obviously these created the softest light of all and also ended up giving us two very different images created by the shadows.


So in the end I think that the images above do show that light size is effected by the three lighting zones. What was interesting to me, as a lighting newbie, was the effect of the light on the subject AND the difference in power needed to get similar exposures with difference lighting.

Now onto the next lessons...

Please feel free to leave comments or questions about this article and I will endeavor to answer them as soon as possible.

Previous lessons from Lighting102:

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