The depiction of time dilation that is typically used to describe the situation, shows the stationary photon clock, with mirrors one above the other in the observer's frame and the photon "bounces" back and forth between them. In the moving frame the mirror pair moves as a unit let's say to the right and the photon bounces at an angle to these mirrors...and from this geometry the longer length traveled by the photon (always traveling at c) is the "cause" of time dilation. My problems are: why does the photon bounce at an angle to the mirrors? the motion (angled trajectory) of the photon should not be dependent on the mirror's motion to the right, only to the angle of the mirror's surface. So I think that depiction is not correct and some change in the angle of the mirrors is required. OR is the photon shown as a bouncing point not accurate and should be shown as a circular wave front propagation thus intercepting the displaced mirrors at greater distance? Thank you for your help.