Slobodan I will try and answer your question. There are 2 simple ways of explaining light and how it acts, (corpuscular aka small particles (photons)) and (waves). Scientists pick the model that explains the phenomena and use it to predict what would happen in different circumstances, this also gives a handy test to see if the model (hypothesis) holds true. Theories that explain diffraction, refraction, reflection have been in place since the 17th Century. Diffraction is easily understood if we think of light as waves, trying to use the photon model leads to ever more complicated fudges with rubbish like photons are attracted to electrons in the aperture blades as they pass close to them. What is argued by Tony Northrup is that photons pass through the middle unmolested leading to the centre of the image being sharp and photons passing close to the blades are bent leading to blurring, ok this makes sense but close the lens down and predict what happens, less go through the centre so the central area is still sharp but this area will be smaller than when wide open. Also more of the light will be passing close to the edges of the aperture so the non central part will be increasingly more blurred as the lens is further stopped down. Unfortunately for Tony N this is simply not the case, as we stop down the edges become sharper in reality. He is also wrong with his diagrams of how images are formed on the sensor showing that he has forgotten his high school Physics. All of the Optics theory needed to design lenses was understood by Huygens in 1670. His theory however would not explain how light produces signals in sensors or how do we get noise in the shadows even if we are using the latest and greatest sensor from Sony or Phase One for that you need to think of photons. What is difficult to understand is how can light behave as a wave in one instance and as a particle in another and the answer is that it is neither but behaves is both in different circumstances but I will leave you with that question because I spent 4 years studying Physics and although I could answer that question the enquiring mind would ask “but why” and this would quickly lead to increasingly weird and wonderful theories and ever more complicated mathematics and the limit of my knowledge. Sorry if this sounds like a teacher talking. Ken
