Please educate me on how it is. I see people spead this myth around alot. I guess they heard it off the internet. I used to manage and still have an office by classical optics scientist for gov. work, and they helped educate me on the matter. I moved on to nonlinear fiber optic transmission instead of classically lense optics. Which is different mind you. Anything you can do to increase your surface area to let more light in helps. Don't matter if you got 10mm tube, the larger your objective the more tranmission you will have. Thats assuming the index of refraction is matched almost perfectly to the air and you lenses are shapped perfectly to route that light to the small internal lenses. Using a 50mm tube would be even better than a 30mm tube. After that you can't gain until you raise your objective.