Apparent Light Size

The third assignment from the Strobist site is an exploration of 'Apparent Light Size'. This follows on nicely from 'Angle' and 'Distance'. There is a general misunderstanding that the hardness or softness of light is a function of the source. Light from an umbrella or softbox will be soft, light from a bare flash or the sun will be hard. Strobist very nicely points out that the reality is that the softness or hardness is actually a function of the apparent size of the source relative to the subject. The bigger the relative source, the softer the light.
The exercise required that we photograph a piece of fruit while keeping the camera to subject position constant and the light to subject angle constant. Light size and distance was varied.
The first image was taken with a bare flash 300mm from the apple at 70 degrees to the camera and slightly above. This is the smallest apparent light size in the examples. The shadow is clearly defined and the light would definitely be described as hard. The highlight from the flash can be seen on the apple.

The second image was taken with the strobe 600mm away. I have failed slightly by not keeping the vertical angle to the subject constant. This has resulted in a lengthening of the shadow. It is however possible to see that the shadow to light transition area (penumbra) is shorter. The shadow edge is sharper. With the increase in distance the apparent light size is even smaller.
Image three has the flash even further away at 1500mm. Again the shadow is lengthened due to decreased vertical angle but this is not the point of this exercise. The apparent light size here is the smallest in all of these examples and yields the sharpest penumbra. The shadow is not as dark but this is because I opened the camera aperture rather than increase the flash power to keep the exposure correct. The ambient light has therefore lightened the shadow slightly.

The second three images are taken using a white translucent umbrella. The flash is shot through the umbrella. The first image is again the closest at 300mm. Comparing this with the bare flash is very instructive. The apparent light size here is the biggest of all the examples. There is still a shadow but it is minimal and the real difference is the very gradual change from light to shadow. Also of significant note in this image is the hardly noticeable highlight. It is hardly noticeable because it is so large. The other very significant point here is the less well defined transition from light to shadow on the body of the apple itself. Clearly, in the case of portrait photography this is desirable. There is enough of a difference to create the impression of three dimensions without harsh shadows cast by facial features.

The final two images show the increasing shadow due to vertical angle change again (not the point of this exercise!). They also show the light to shadow transition becoming slightly harsher again.

Even though we have a 115cm diameter light source, as it gets further away it's apparent size is reducing even though it is still big compared to the bare flash.

The most extreme example of apparent light size from a photographers point of view is the sun. It is also the most commonly used light source! The sun is the biggest light source a photographer will ever use but paradoxically it normally supplies some of the hardest light. The reason for this is the 93 million miles that lies between the source and the subject. It can of course supply very soft light but this will be because of cloud or fog or some other atmospheric effect. This is in effect adding a very large umbrella or softbox.

Light Relief

There is no Strobist assignment as such this week so I will take the opportunity to blabber on about something else. I've added a Favourite Links section in the right hand column. If anyone is looking for some light relief, check out What The Duck. Here is an example:









Some of these are so 'spot on' you can't fail to be amused by them. I can't help myself, so here's another:









The Online Photographer which is also linked is an excellent blog on various photographic topics. The Nikonians forums are superb resource for all issues related to Nikon equipment. Should you feel the urge to follow the biggest cycle race on the planet over the next three weeks then http://www.cyclingnews.com/ is arguably the best website for doing this.

Black Background

The second exercise in the Lighting 102 course at http://www.strobist.blogspot.com/ is concerned with the ratio of flash to subject distance and flash to background distance. Control of this ratio allows the relative darkness of the background to be fully controlled. All of these images were shot at ISO200 with a shutter speed of 1/200th second. The subject is 1.5m from the background and the flash is at approximately 45 degrees to the right. The starting aperture was f5.6 with 1/8 power on a Nikon SB800 speedlight. As the flash to subject distance was decreased the power and aperture were reduced as required to achieve a good exposure.

The first image was taken with the flash 5m from the subject. Clearly enough light is hitting the background to make it appear similarly exposed.
The flash is now 2.5m from the subject and the background is getting darker. This happens because the fall off of light intensity is proportional to the inverse of the square of the distance.
The background of the third image is getting quite dark (flash 1m away from subject). Notice how the nose shadow is also darker. This will be because in the earlier images enough light was being reflected back from a wall to the left to soften the shadow. The 'Depth of Field' of the light is now so shallow that this no longer happens.

Now we're talking! The background is now really dark (flash 45cm away from subject) and the fifth image (below) which is taken with the flash 30cm away from the subject is nearly black.


I couldn't quite achieve black so I think I need my light even closer or my subject a bit further from the background. The ambient contribution is non existent at these settings (ISO200, 1/200th, f11) so any light is from the flash. This exercise has been a real eye opener for me as I have often wondered how to control this aspect of flash photography. The 20 minutes spent doing this exercise has taught me so much. Blasting away with TTL flash systems can be handy at times but this stuff is much more fun.
However, for the next exercise I will probably be using an inanimate object. Triggering the self timer and dashing round to get in the shot is likely to end in a knocked over lightstand.

Hard Light

The first Strobist exercise was posted last week and comprises a brief exploration of the shadows created by hard light from an off camera strobe at various angles to the subject.
The first image here shows the subject with camera directly in front with the strobe at 45 degrees to the right. The shadow on the wall is very nasty. The subject has been left close to the wall to emphasise this. The speedlight is actually a fair bit higher than the subject which can be seen by the downward slope of the shadow.

The second image shows the effect of the camera at 45 degrees to the left of the subject with the speedlight remaining at 45 degrees right. The wall shadow is equally harsh.

The third and final image shows the camera position at the same position as the speedlight at 45 degrees right. This is equivalent to on camera flash except that the speedlight is higher than the camera. Illumination of the face is more even which is not necessarily a good thing as the image will often look too flat. This is the main problem with on camera flash. The harsh shadow is still visible on the wall.

Land of the Long White Cloud

Hello from New Zealand or Aotearoa in Maori (the land of the long white cloud). This is my first post in a blog and I initially intend to use it to track my progress on the Lighting 102 course currently running at http://www.strobist.blogspot.com/.

Strobist is an excellent blog which focuses on the techniques of off camera lighting. The first assignment is coming this week and I will report here with progress.

Although I have been interested in photography for 20 years, the digital revolution has re awakened my enthusiasm. The ease with which the whole darkroom process can be reproduced in the living room has captured my imagination. Other aspects of my new path of learning in photography will be also be discussed here.