In the δAsn20 Drosophila stock, the N-linked glycosylation site of opsin in Rl-6 receptors (Rhl) is absent. We used electroretinography (ERG), microspectrophotometry (MSP), and electron microscopy (EM) to quantify visual cell defects. Positive controls, w9, had wild type Rhl. MSP revealed minimal photopigment in δAsn20 for 6 days posteclosion; w9 had near normal visual pigment. ERG sensitivity and prolonged depolarizing afterpotential (PDA) were compared for δAsn20 and w9. δAsn20's Rl-6 function is decreased 100–fold at eclosion and diminishes until only R7/8 functions at 11 days. What little rhodopsin is routed to the rhabdomere functions. Morphometry showed smaller Rl-6 rhabdomeres in δAsn20 for 8 days posteclosion. Rhabdomeres in w9 were normal. A negative control, ninaE0117, a deletion of the Rhl gene, also has small rhabdomeres. δAsn20 and ninaE0117 lack the extreme rhabdomere elimination of ora (outer rhabdomeres absent), a nonsense mutant interrupting Rhl's coding sequence. δAsn20 and ora have surplus membrane while ninaE0117 does not. Freeze fracture reveals that δAsn20's rhabdomeric P-face particle count is as low as for vitamin A deprivation, consistent with an opsin defect. High particle density, organized into rows, is present in adjacent plasmalemma where surplus membrane accumulates. In summary, δAsn20 interferes with either synthesis, deployment, or maintenance of opsin.