Thank you for your answer Arsene Lupine
It makes sense, but I’m not sure that it is absolutely true. The focus of any lens doesn’t depend from the quantity of light passed through it (but may be the source management affects it). After many time in contemplation
, my conclusion is that the Betty/Wilma stand is a little bit tilt to the ground in relation to the Piko’s one. You paid my attention to the over burned spots in front of the lights and I think that this effect is actualy caused from a little stand tilt.