Calibrating simple microscope system with CCD

Hi :)

I've got problem with calibrating simple microscope system.
I use a CCD beam profiler from Melles Griot (WinCam D), because I would
like to scan with help of it light profile that passed through planar
waveguide I need to build simple microscope system that will cooperate
with CCD of my beam profiler. For that purpose I used a standard
microscope objective (for tube length 160 mm - if it works with
eyepiece) and tube that I matched experimentally (approximately 120
mm). The problem lies in calculation of the magnification of such
system. (I need to know the magnification to estimate the beam size) I
know that it depends on tube length and magnification of the microscope
objective ( I dont use an eyepiece), but I dont know any mathematical
relation.

I hope that you can help me.
Thanks in advance.

Andrew

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