Shooting Video with Nikon D5100 and Sigma DC 18-200mm 1:3.5-6.3 HSM? - 1

Hi i'm looking to shoot video with my nikon camera, and sigma lens. But i'm struggling to focus the camera it doesn't seem to focus at all when filming. And the focus is always red.could this be because of my lens? I also try to take photos in live view… And they never focus and again the focus is red… Does anyone know the settings that will work? I have been searching but most say what i already doing.

is the lens the problem or the camera?

First thing, you can't do "filming" with a digital camera because these cameras don't use film… They record video.

Video is difficult with these very light weight cameras to begin with… I know because I do lots of video with my Canon dslr and did a career in broadcast television camera work… Not film.

I'd opt first for a much shorter lens, say your 18-55 especially if it's VR… If not get a VR lens.
Learn manual focus. Yes your lens will focus during video if you know how to operate it correctly… Practice is the key to learning.

Get off of live view for still shots. Use the view finder.

Bottom line is this lens is way to heavy and long to be effective for video and I think that's your entire problem.

Most video is shot using some kind of script and each scene is manually focused.

Your D5100 has an electronic rangefinder you can use to focus your shots.

The big boys in Hollywood always manually focus the camera when shooting a film, in fact there's one assistant called a "focus puller" whose job it is to keep the subject or scene in focus.

You may find this link helpful.

https://vimeo.com/...m/15928756

This link will show you want other accessories you really need to make a dSLR still camera with a video feature into a viable video camera.

As you can see, your D5100 and 18-200 mm lens is just the tip of the iceberg