Hi, I am relatively new in optics and OpticStudio. I am trying to simulate the spot size at certain distance from a lens while using a fibre as source. Spot size changes as we move the image plane further from the lens as expected. But I am not seeing it change as I move the image plane from 330mm to 600mm. Not sure why. 

Second question is when I do a quick fucus, it doesn’t bring the image plane in the focus. But when I set the Thickness cell to marginal ray height it does move the image plane to the right position. Any help will be highly appreciated. Thank you.