Understanding the deflagration-to-detonation transition (DDT) is critical for various combustion-related fields, from manufacturing safety to jet propulsion. As opposed to typical, application-sized studies, recent investigations use microtubes due to cost-effectiveness and environmental impact. This study captures the flame front of detonation waves during DDT through five diameter step changes with a high-speed camera. The results indicate all diameter changes result in a velocity drop before re-detonation occurs at a critical velocity.