diff --git a/src/backprojector.cpp b/src/backprojector.cpp
index 212ba0ad5..511fbb80d 100644
--- a/src/backprojector.cpp
+++ b/src/backprojector.cpp
@@ -1209,6 +1209,8 @@ void BackProjector::externalReconstruct(MultidimArray<RFLOAT> &vol_out,
                                         MultidimArray<RFLOAT> &tau2_io,
 										MultidimArray<RFLOAT> &sigma2_ref,
 										MultidimArray<RFLOAT> &data_vs_prior,
+										RFLOAT pixel_size,
+										RFLOAT particle_diameter,
 										bool is_whole_instead_of_half,
                                         RFLOAT tau2_fudge,
                                         int verb)
@@ -1257,6 +1259,8 @@ void BackProjector::externalReconstruct(MultidimArray<RFLOAT> &vol_out,
 	MDlist.setValue(EMDL_MLMODEL_DIMENSIONALITY, ref_dim);
 	MDlist.setValue(EMDL_MLMODEL_ORIGINAL_SIZE, ori_size);
 	MDlist.setValue(EMDL_MLMODEL_CURRENT_SIZE, 2*r_max);
+	MDlist.setValue(EMDL_MLMODEL_PIXEL_SIZE, pixel_size);
+	MDlist.setValue(EMDL_OPTIMISER_PARTICLE_DIAMETER, particle_diameter);
 
 	MDtau.setName("external_reconstruct_tau2");
 	for (int ii = 0; ii < XSIZE(tau2); ii++)
diff --git a/src/backprojector.h b/src/backprojector.h
index 02026a0d2..b85a6fedc 100644
--- a/src/backprojector.h
+++ b/src/backprojector.h
@@ -299,6 +299,8 @@ class BackProjector: public Projector
 	                         MultidimArray<RFLOAT> &tau2_io,
 							 MultidimArray<RFLOAT> &sigma2_ref,
 							 MultidimArray<RFLOAT> &data_vs_prior,
+							 RFLOAT pixel_size=1,
+							 RFLOAT particle_diameter=0,
 							 bool is_whole_instead_of_half = false,
 	                         RFLOAT tau2_fudge = 1.,
 	                         int verb = 0);
diff --git a/src/ml_optimiser.cpp b/src/ml_optimiser.cpp
index 5643b0928..1f0cac665 100644
--- a/src/ml_optimiser.cpp
+++ b/src/ml_optimiser.cpp
@@ -4612,6 +4612,8 @@ void MlOptimiser::maximization()
 							mymodel.tau2_class[iclass],
 							mymodel.sigma2_class[iclass],
 							mymodel.data_vs_prior_class[iclass],
+							mymodel.pixel_size,
+							particle_diameter,
 							(do_join_random_halves || do_always_join_random_halves),
 							mymodel.tau2_fudge_factor,
 							1); // verbose
diff --git a/src/ml_optimiser_mpi.cpp b/src/ml_optimiser_mpi.cpp
index b324b92dd..245a3c302 100644
--- a/src/ml_optimiser_mpi.cpp
+++ b/src/ml_optimiser_mpi.cpp
@@ -2040,6 +2040,8 @@ void MlOptimiserMpi::maximization()
 									mymodel.tau2_class[ith_recons],
 									mymodel.sigma2_class[ith_recons],
 									mymodel.data_vs_prior_class[ith_recons],
+									mymodel.pixel_size,
+									particle_diameter,
 									(do_join_random_halves || do_always_join_random_halves),
 									mymodel.tau2_fudge_factor,
 									node->rank==1); // only first followers is verbose
@@ -2176,6 +2178,8 @@ void MlOptimiserMpi::maximization()
 										mymodel.tau2_class[ith_recons],
 										mymodel.sigma2_class[ith_recons],
 										mymodel.data_vs_prior_class[ith_recons],
+										mymodel.pixel_size,
+										particle_diameter,
 										(do_join_random_halves || do_always_join_random_halves),
 										mymodel.tau2_fudge_factor);
 							}