  The geodesic method has played a crucial role in understanding the circular
orbits generated by compact objects, culminating in the definition of the
photon sphere, which was later generalized to a photon surface in arbitrary
spacetimes. This new formulation extends the concept of the photon sphere in a
broader sense, including dynamical spacetimes, as shown by the Vaidya solution.
The photon surface essentially defines the null geodesics, which are originally
tangent to the temporal surface, and keeps them confined to this surface.
However, this formalism does not cover all classes of particles, and to
overcome this limitation, a more comprehensive approach, denoted as the
"massive particle surface", has been proposed that also accounts for charged
massive particles. Indeed, the photon surface concept is recovered when the
charge and mass of the particles are zero. In this work, we use these three
formalisms to check the consistency of the results for the values of the radius
of the photon sphere ($r_{ps}$) and the radius of the "innermost stable
circular orbit" (ISCO) ($r_{\rm ISCO}$) for some gravitational models. In our
results, the first model is described by conformal gravity, with the
peculiarity that $g_{00}\neq-g_{11}^{-1}$. The second model, i.e. the Culetu
solution, is developed by coupling General Relativity with nonlinear
electrodynamics, which requires the consideration of the effective metric
($g_{\rm eff}^{\mu\nu}$) for geodesic approaches. Furthermore, we have also
analysed the expressions for $r_{ps}$ and $r_{\rm ISCO}$ in a general static
and spherically symmetric metric. Under these circumstances, we have found a
discrepancy of $r_{ps}$ and $r_{\rm ISCO}$ obtained by the massive particle
surface formalism as compared to the geodesic and photon surface formalisms.
