I saw Sony DSR-PD170 has a lens says F1.6to2.4 , but Panasonic AG-DVC30 has a lens of F1.6, does it mean Sony has a better lens ? and about Filter diameter, true that the bigger the better it is ?

The quality of a lens is not measured by the maximum lens opening (f/1.6 vs. f/2.0 for example) nor is it measured by filter size. Lenses can be compared objectively by their MTF (http://www.luminous-landscape.com/tutorials/understanding-series/understanding-mtf.shtml) (modular transfer function) and subjectively by your eye (do you like the image your camera produces).

Jeff,

I fully agree to what you said. However, the maximum lens opening may be important in low light situations and, of course, if you want a shallow depth of field.

T-Stops are more relative than F-stops when it comes to lens speed.

<<<-- Originally posted by Richard Alvarez : T-Stops are more relative than F-stops when it comes to lens speed. -->>>

This is true of course. But for zoom lenses with roughly the same number of elements and similar multicoating the difference in T-stops should not be too large.

Or is there a flaw in my thinking?

If there is a flaw, it lies in the words "similar" and "roughly". No guarantee that the t-stops for "Roughly simlilar" lenses would be the same. The question "Does Sony have a better lens" is of course subjective in terms of visual aesthetics, but by measurable quantitites, Jeff's reference to MTF is correct.