After several years of flying under the radar and letting competing showcases take root, the Boston Film Festival is getting organized early and seems ready to take off for its 26th edition. Executive director Robin Dawson has set Sept. 17-23 as the time for this year’s fest, soliciting entries in the feature, documentary, animated and short categories. One day will be devoted to ecologically-themed films.The fest will be newly headquartered at the Stuart Street Playhouse, an independent venue run by David Bramante, operator of the West Newton Cinema arthouse in the Boston suburbs. The refurbished 425 theater is a showplace striving to gain a toehold in the competitive Boston market dominated by AMC’s Boston Common and Regal’s Fenway multiplexes. It is located in the downtown area just blocks from Boston’s legit theater district. Those interested in submitting their films for consideration may use the Without a Box website or go to bostonfilmfestival.org.