TITLE: GCN CIRCULAR NUMBER: 10783 SUBJECT: GRB 100418A: CrAO optical observations DATE: 10/05/19 19:25:13 GMT FROM: Alexei Pozanenko at IKI, Moscow V. Rumyantsev (CrAO), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of the Swift GRB 100418A (Marshall et al. GCN 10612) with Shajn telescope of CrAO between (UT) May, 14 21:07 -- 22:48 under photometric weather conditions and mean seeing of about 2 arcsec. The preliminary photometry of the afterglow+host in a stacked image based on USNO-B1.0 star 1014-0271368 (RA(J2000) = 17:05:26.42 Dec(J2000)= +11:27:32.9) assuming R=17.32 is following: T0+ Filter, Exposure, mag. (mid, d) (s) 26.0332 R 90x60 21.86 +/-0.06 The photometry is compatible with R-magnitude reported by Perley et al, GCN 10727 (R=21.85+/-0.05 at 17.739 days) and still brighter than assumed R-magnitude of the normal type of host galaxy (SDSS based ugriz-> R conversion) which cannot be explained solely by afterglow contribution fading steeper than power law with decay index of .~0.8.