To observe temporal changes in the nectar volume of Impatiens flowers, we modified and used an interval-shooting camera with a special flash system. Former methods of measuring nectar volume inevitably necessitated destruction or damage of the floral parts. As a consequence, accurate continuous measurements of nectar volume under natural conditions have been difficult. While considering how to overcome this problem we noticed that when flowers were observed against transmitted light from the sun, a silhouette of nectar was visible inside the spur. To exploit this phenomenon, we attached a polymer optical fiber to the built-in flash of a compact digital camera and bent the fiber towards the camera's lens to provide backlighting. We took interval images and estimated the nectar volume from the size of nectar silhouette. To our knowledge, this is the first reported method involving the use of time-interval photography for measuring nectar volume in situ.