We investigate the viable exponential f ( R ) gravity in the metric formalism with f ( R ) = - \beta R _ { s } ( 1 - e ^ { - R / R _ { s } } ) .
The latest sample of the Hubble parameter measurements with 23 data points is used to place bounds on this f ( R ) model .
A joint analysis is also performed with the luminosity distances of Type Ia supernovae and baryon acoustic oscillations in the clustering of galaxies , and the shift parameters from the cosmic microwave background measurements , which leads to 0.240 < \Omega _ { m } ^ { 0 } < 0.296 and \beta > 1.47 at 1 \sigma confidence level .
The evolutions of the deceleration parameter q ( z ) and the effective equations of state \omega _ { de } ^ { eff } ( z ) and \omega _ { tot } ^ { eff } ( z ) are displayed .
By taking the best-fit parameters as prior values , we work out the transition redshift ( deceleration/acceleration ) z _ { T } to be about 0.77 .
It turns out that the recent observations are still unable to distinguish the background dynamics in the \Lambda CDM and exponential f ( R ) models .