Many research reactors enable neutron radiography applications. Thus, reactor design and operational management requires prediction of the neutron flux for the efficient imaging in the neutron camera facilities. Reactor neutronic calculations use Monte-Carlo codes which are effective for computing the flux at the core immediate vicinity, but when trying to calculate the flux at the end of a neutron beam channel, simulations are restricted. Since the vast majority of neutrons do not arrive to that location, and one needs to spend extensive calculation resources which hardly add statistical relevance for the region of interest at the imaging plane. Here, we discuss the development of a novel analytic method based on transport theory which uses Monte-Carlo calculation results of the neutron flux at around the reactor core, and deternines the flux at the imaging plane. The scheme locates the origins of the ballistic neutrons, and tally the flux there, providing an estimate of the beam strength. We validated the method by comparing the results to MCNP Calculations and to past measurements in the Israeli Research Reactor 1 (IRR1). Consequently, this method may help optimize the IRR1 core for radiography, potentially increasing efficiency by about 50%. The method is relevant to different neutron beam sources and applications, such as accelerator based neutron sources and diffractometers.