I thought at this point to add some more examples of implicit triangles. It was fun looking for these and the results I wanted to share here.
Triangle 1: ISO 200 300mm f16 1/125
An opportunist photograph above with the children unwittingly creating an implicit triangle. The rill flowing from a higher lake to the formal lake was stepped enabling them to be at different levels. The long focal length has flattened the perspective creating a very obvious triangle.
Medieval cloth: ISO 3200 35mm f4 1/50
At this moment, as the seller was organising her rolls of medieval cloth in one of the barns in Cressing Temple two triangles were formed. A smaller triangle with her head as the apex and the base being the roll of cloth which she is holding and the much large triangle extending from there down to the base of the photograph itself. The larger triangle being caused through perspective and the use of the wide-angle lens. The location was at the back of the barn with very little natural light. I used Auto WB here and have since considered altering this, but did not like the effect of additional blue and the warm colour was much closer to the feeling I had when there.
Preparing Onions: ISO 200 310mm f5.6 1/2500
Here the implicit triangle is formed through the arms leading to a point in the onion on the chopping board. This device helps to focus the viewers attention on the subject which is the action of slicing an onion. I focused carefully on the fingers and had the aperture fully open in order to have as shallow DOF as possible.