For structural beams, what matters in their resistance to deflection is their second moment of area (often referred to as moment of inertia) or "I".
If you have two beams that are made of the same material same length, all you have to do to compare their stiffness is compare their I's.
For a square hollow beam with cross section dimensions
For a round hollow tube with cross section dimensions
Now if you want to take in account the length and material, you need to introduce:
E=modulus of elasticity (property of material, may be found on matweb.com)
q= lb/ft weight of the beam per foot (approx. cross sectional area * density)
P=load due to camera mounted.
δ1=max deflection (at the end of the beam) due to the weight of the beam.
δ2=max deflection (at the end of the beam) due to weight of the camera.
δt=max total deflection
δ1 = (q*L^4)/(8EI)
δ2 = (P*L^3)/(3EI)
δt = δ1+δ2
-Camera is mounted at the end of the beam.
-Weight of the beam is uniformly distributed.