  We present updated preliminary results for the nucleon electromagnetic form
factors for non-perturbatively $\mathcal{O}(a)$ improved Wilson fermions in
$N_f=2$ QCD measured on the CLS ensembles. The use of the summed operator
insertion method allows us to suppress the influence of excited states in our
measurements. A study of the effect that excited state contaminations have on
the $Q^2$ dependence of the extracted nucleon form factors may then be made
through comparisons of the summation method to standard plateau fits, as well
as to excited state fits.
