The QF67A provides even distributed light with close to medium range shots. When using this diffuser with the T5d-R flash, you will lose one full stop of light output. The softness of light output that this diffuser provides, is to be preferred over the standard flat diffuser that comes with the T5d-R unit. Forty feet or less at ISO 200 with a Quantum TTL module for your specific camera should permit one to pretty much run and gun with excellent soft light illumination that most hot shoe mounted flash units can't compete with.