Relation between the lens search performance and the seeing in each single epoch from the HSC transient survey. The quantity d_t is defined as the minimum distance between (TPR, FPR) = (100%,0%) and the ROC curve of the bright lensed quasars (m_3rd <  22.0 mag) with wide separation (θ_LP >  1.5″) for each epoch t. The 13 star symbols indicate the d_t values for the 13 epochs, plotted against their corresponding seeing. Our lens search algorithm performs well when the single epoch has seeing ∼0.7″. The low lens search performance in the epoch with extraordinary seeing (< 0.5″) is due to the significant artifacts in the difference image from the sharp image.