Sorry, if you were to mount this smaller lens onto a larger lens, you will get vignetting. For the PV-GS400, here is a fine fish eye for you. Raynox HDP-2800ES High Definition 0.28x Diagonal Fisheye Conversion Lens B&H # RAHDP2800ES. Yes, it is more expensive but it will work.

According to our shipping specifications, the product will weigh .30 lb.

This ring is to attach a 62mm filter to a 77mm lens thread but for wide lenses, that's a no-no, vignetting will occur.

No. The 58mm side is male and screws into the lens. The 49mm side is female and receives the filter's male threads.

The Sensei 52-48mm Step-Down Ring has female 48mm threads on the front of the ring to allow you to connect a filter with 48mm male threads to the step-down ring. The back of the step-down ring has 52mm male filter threads which will screw into the 52mm female filter threads on the front of your lens.

I am using this step with a Canon EFS 10-22mm. At 10mm there is minor vignetting only in the extreme corners, but it is barely noticeable. When I zoom out to 11mm and beyond, the vignetting goes away completely. I typically post process my macro shotsand crop closer to the subject. I have never noticed the vignetting until you asked this question. I had to setup a shot and test it to give you an accurate answer. In my opinion, the product is 100% acceptable.

Yes.

Yes you use more than one step down adapter ring. Note you will get a lot of vignette when using that setup of 77 lens filter thread to a 49mm filter.