Dear Suhad Yasin,  As per as my knowledge you can measure it, for that you have to define the resolution with the defined measurement of any object after that you can measure the diameter of fiber by calculating the pixel with that resolution.  Thanks  

Thank you very much....for your answer.

I think you can for microscale fibres but you need to make your own scale. If the microscope is mounted  with a digital camera the digital image can be analysis by AutoCAD software so all your fibres will measure according to your own scale. Finally, I would not recommend this process for submicron spun fibres. Good luck