Directional Light, Smooth Reflective Surface and Diffusion

[mjkzz]

While trying to stack a white crystal and moving lights around to get a good lighting angle, I encountered something that was discussed in this thread Back at that thread, it is hard to imagine that geometry changes, even though Rik has shown an animated picture. Seizing the opportunity, I recorded a video showing just that and upload it on Youtube.

Not only that, I have set it up to demonstrate what happens when there are two lights positioned as a setup shown below.


Here is the picture when light A is lit and B is off


Here is the picture when light B is lit and A is off. Notice that in this picture, the subject is NOT as focused as the previous one. I guess this is due to the fact different ray of lights entered the lens and their path is different and appear to be from farther away (or nearer) even though physical distance between lens and subject did not change.


And here is the magical picture when BOTH A and B are lit. Here you can see, just like Rik said, it looks like a composition of above pictures!!!


However, when lights are diffused, focused area are not affected much by moving lights around as shown in video.

So, if you are shooting some highly smooth and reflective subject, diffusion is not just for aestheicts, but also for sharper images because regardless how good stacking algorithm is, directional light will cause problems.

[mawyatt]

Peter,

Thanks for posting this and the video. I know I use heavily diffused light for chip images, but seeing your video makes the reasoning crystal clear!!

It's amazing to see how much effect the lighting has.

Best,

Mike

[abpho]

Thanks Peter. Great video. Very interesting to see this.