with a tether of length $L=901\,$bp and a 490$\,\nmunit$ diameter bead. Error bars were drawn using the same method as in . Each point has been normalized to the data at 1ms to give a dimensionless quantity on the vertical axis. *Curve:* Expected correction due to finite shutter speed, calculated by the method in the text (), with shutter time given on the horizontal axis (see also the Supplement to [@Towles2008]). ]{}](calibrationfigPN/KBT_blur.eps "fig:"){width="3.1truein"} ![\[fig:exposure\][RMS bead excursion as a function of camera shutter time in milliseconds. *Dots:* Experimental data. Each dot represents about $20$ different observed beads, with a tether of length $L=901\,$bp and a 490$\,\nmunit$ diameter bead. Error bars were drawn using the same method as in . Each point has been normalized to the data at 1ms to give a dimensionless quantity on the vertical axis. *Curve:* Expected correction due to finite shutter speed, calculated by the method in the text (), with shutter time given on the horizontal axis (see also the Supplement to [@Towles2008]). ]{}](bitmaps/KBT_blur.eps "fig:"){width="3.1truein"}

In our experiments the camera had a long shutter time ($\delta t=31\,\msunit$). During each exposure, the bead moved, creating a blurred image whose center is not quite the same as the 