  We analyze the effects of the detector response time on bolometric
measurements of the anisotropy of the cosmic microwave background (CMB). We
quantify the effect in terms of a single dimensionless parameter $L$ defined as
the ratio between the time the beam sweeps its own size and the bolometer
response time. As $L$ decreases below $\sim 2.5$ the point source response of
the experiment becomes elongated. We introduce a window function matrix based
on the timestream data to assess the effects of the elongated beam. We find
that the values of the window function matrix elements decrease slowly as a
function $L$. Our analysis and results apply to other cases of beam asymmetry.
For the High Frequency Instrument on board the Planck Surveyor satellite we
show that for a broad range of $L$ the ability of the experiment to extract the
cosmological parameters is not degraded. Our analysis enhances the flexibility
in tuning the design parameters of CMB anisotropy experiments.
