Magnification of a system of lenses

I have a lens system consisting of 7 elements. However, I cannot take the system apart to measure the distance between them or their focal lengths. I do, however, know the effective focal length of the whole system. Is there a way to calculate the magnification of the whole system (for a given image distance)?

If your system is equivalent to a single lens with focal lenght $$f$$, then you can proceed like if you had one only lens with that $$f$$, so $$M_L=\frac{s'}{s}$$, with $$s$$ the distance to the object