A deposition system for guiding a flexible substrate along a path past one or more heating evaporation sources, the deposition system comprising: a deposition chamber, comprising: a payout hub for unwinding a flexible substrate in a -X-direction; a first actuator coupled to the payout hub, the first actuator operable to adjust a position of the payout hub in a Y-direction perpendicular to the X-direction; a first optical position sensor assembly configured for measuring a position in the Y-direction and located a first distance in the -X-direction from the payout hub; a second optical position sensor assembly configured for measuring a position in the Y-direction and located a second distance in the -X-direction from the payout hub; one or more payout tractors (410, 415) positioned to engage a side of the flexible substrate when looking down a -Z-direction; and one or more evaporation sources for heating material inside the one or more of the evaporation sources and directing evaporated material towards a front side of the flexible substrate facing the one or more evaporation sources as the flexible substrate is conveyed past the one or more evaporation sources in an X-direction; and a pickup hub; wherein the first optical position sensor assembly is configured to measure a third distance of an edge of the flexible substrate in the Y-direction; the second optical position sensor assembly is configured to measure a fourth distance of the edge of the flexible substrate in the Y-direction; an optical position sensor assembly (115, 116) comprises a light source positioned above the flexible substrate for emitting blue, violet, or ultraviolet light rays towards a light sensor positioned below the flexible substrate; and there is no line of sight in the deposition chamber from the one or more evaporation sources to any of the optical position sensor assemblies (115, 116) when the flexible substrate is connected from the payout hub to the pickup hub. a deposition chamber, comprising: a payout hub for unwinding a flexible substrate in a -X-direction; a first actuator coupled to the payout hub, the first actuator operable to adjust a position of the payout hub in a Y-direction perpendicular to the X-direction; a first optical position sensor assembly configured for measuring a position in the Y-direction and located a first distance in the -X-direction from the payout hub; a second optical position sensor assembly configured for measuring a position in the Y-direction and located a second distance in the -X-direction from the payout hub; one or more payout tractors (410, 415) positioned to engage a side of the flexible substrate when looking down a -Z-direction; and one or more evaporation sources for heating material inside the one or more of the evaporation sources and directing evaporated material towards a front side of the flexible substrate facing the one or more evaporation sources as the flexible substrate is conveyed past the one or more evaporation sources in an X-direction; a payout hub for unwinding a flexible substrate in a -X-direction; a first actuator coupled to the payout hub, the first actuator operable to adjust a position of the payout hub in a Y-direction perpendicular to the X-direction; a first optical position sensor assembly configured for measuring a position in the Y-direction and located a first distance in the -X-direction from the payout hub; a second optical position sensor assembly configured for measuring a position in the Y-direction and located a second distance in the -X-direction from the payout hub; one or more payout tractors (410, 415) positioned to engage a side of the flexible substrate when looking down a -Z-direction; and one or more evaporation sources for heating material inside the one or more of the evaporation sources and directing evaporated material towards a front side of the flexible substrate facing the one or more evaporation sources as the flexible substrate is conveyed past the one or more evaporation sources in an X-direction; and a pickup hub; wherein the first optical position sensor assembly is configured to measure a third distance of an edge of the flexible substrate in the Y-direction; the second optical position sensor assembly is configured to measure a fourth distance of the edge of the flexible substrate in the Y-direction; an optical position sensor assembly (115, 116) comprises a light source positioned above the flexible substrate for emitting blue, violet, or ultraviolet light rays towards a light sensor positioned below the flexible substrate; and there is no line of sight in the deposition chamber from the one or more evaporation sources to any of the optical position sensor assemblies (115, 116) when the flexible substrate is connected from the payout hub to the pickup hub.