Portable imaging viscometry for quantitative complex fluid measurements

•A portable viscometer based on microrheology is demonstrated.•The portable viscometer is sensitive to complex moduli down to 0.23 mPa.•The static error for the portable viscometer is quantified to be 10–100 nm.•Portable viscometer performance we measured to be within 4–6% of comparable microscopy experiments.•Not accounting for finite exposure time in data analysis can underestimate viscosity by 7%.