The photoreceptors of newly eclosed flies expressing inaD^ninaE.T669A in a inaD^T1 mutant background show a slower response to brief (1ms) flashes containing ~75 effectively absorbed photons. Peak amplitude is similar to wild type but the time to peak is delayed and the decay time course is slower. Following 1s light steps of increasing intensity wild type responses consist of an initial peak that rapidly declines to minimum (the "notch"); this "notch" is more pronounced in inaD^T1 inaD^ninaE.T669A mutant flies. Although the intensity dependence of both peak and plateau in mutants are indistinguishable from wild-type, the "notch" develops at 2-3 fold lower intensities than in controls.