A million dollar question. You can visit many websites, read reviews and spend a good deal of time but here on this page, I am going to tell you in a few minutes what you need to know about taking professional-looking HD videos.
By now most of us know
most compact cameras, or smartphones like iPhones, are not good
at video recording. This is because their sensors are tiny and so
are the lenses. If the light is good, they do an okay job. When light
is dull, they are almost unusable. The same is true for most consumer
SLR cameras with kit lenses. So what do we do to take high quality
High-Definition videos? Do we need to be stuck with HD Camcorders?
Do they also take nice videos?
Here is what I have found: Most compact cameras don't do a good job in low light- for still images or for videos.
Another option is an HD Camcorder. Most HD Camcorders will do a better job than compact cameras or smartphones most of the time but the video will not be professional looking. The video will be HD but not HQ (high quality). HD Camcorders keep everything in focus most of the time (if not all the time) unless you have one that costs $4000 upwards. With most consumer camcorders, you really can't keep certain things in focus and other things blurred. Unless you have noticed, most HD camcorder videos are plain and boring. If you are fine with this, they can be a good choice for you. You can find some good ones around $200-%500 range.
Now if you have noticed in some professional videos or movies, they often have background blurring. I mean selective focusing where only the subject is in focus to grab all of your attention. There is no other distraction in the frame. With SLR, this is possible because of the large sensors and bigger (I mean wide aperture) lenses. As said earlier, most SLRs don't offer good autofocus so many professional photographers have gone with manual focusing. Many serious Canon users use Canon full frame camera line Mark with some wide aperture and fast lenses. Many of them specifically use Manual lenses with manual focus and one favorite is Super Takumar 50mm F1.4 lens.
One of the best option for an SLR with Auto Focus during video shooting/Movie mode: Currently in Canon T4i, you have a choice of three autofocus modes you can select before recording - Face Detection (with subject tracking), FlexiZone-Single (user-defined AF point) or FlexiZone-Multi (automated AF point selection). Regardless of which AF setting you've chosen, when 'AF w/shutter button during filming' is set to 'On' you can force the camera to reacquire focus with a half-press of the shutter button. Of course, you can also choose to focus manually. All of the touchscreen benefits we enjoyed in shooting stills carry over to video mode as well. The Quick Control menu offers a fast way to adjust settings and you can set the AF point simply by tapping the screen. The camera's articulated LCD screen aids greatly in shooting video from very low or high angles or simply manoeuvering the screen in a more shaded position for glare-free viewing.
For T4i, here is what a reputed Camera Review website DPReview has to say for Auto-focus in T4i: While the results of these changes show noticeable improvement over the EOS 600D, AF in video mode is, unfortunately, still slow. In our time spent using the camera, we've not been able to reliably maintain focus on objects moving to or away from the camera at even a moderate walking pace. As it stands it's hard to envision situations in which continuous AF that is this slow has any practical benefits for tracking moving subjects. As with the EOS 600D, we still recommend shooting video in manual focus, or at the very least pre-focusing the lens with a half-shutter button press before you start recording.
Actually for videos, Manual focus is better than Autofocus in our opinion. (i) Motor of most auto-focus lenses creates some hissing sound during focusing which can create bad audio in your recording. (ii) The Autofocus issue can be worse when trying to focus in low light. (iii) Though some cameras offer Auto Focus, it is still remarkably slow and inaccurate for most DSLs. (iv) Autofocus as the name mentions auto-focuses so if you want to have only person A in focus out of a group of 5 people, you really can't do it on the fly. If want to focus only specific area while shooting a video, you can't do it unless you manually focus on it. (v) Also, most auto-focus lenses don't let you change the aperture on the fly to control depth of field. Old lenses like Super Takumar, let you control focus, and aperture very smoothly.
Don't overlook the Audio part if you are in pursuit of great videos. Videos are not complete without audio. Most consumer SLRs have the body Mic to capture audio. While it works, it is not enough. For best quality, it is important to have an external mic jack so you can input better video directly from the source or from closer to the source. Also, see if a camera records in mono or stereo. Choose a camera that offers Hi Quality audio and the ability to record in 16-bit instead of 12 bit or 8 bit.
I am not an expert but here is one video I recorded in low indoor light with Panasonic GF3 and a Super Takumar 50mm F1.4 screw mount M42 lens. I am still learning manual focus so please bear with me for focus misses. However I am sure this group of 6-year-old kids running/traveling with the ball will not fail to entertain you.
If you are short on budget but want to take nice videos, you can buy a Pentax K-01 body for around $300. Buy a Super Takumar M42 lens for around $100 with an adapter for Pentax. Once you get hold of the manual focusing, you will be amazed at how beautiful videos you can take with a DSLR compared to compact cameras or most consumer SLRs with a kit lens. Even with those HD camcorders.Super Takumars are around 40 years old M42 screw-mount lenses. I used it often on Pentax and Panasonic mirrorless cameras. Here is one video I recorded with Pentax K-01 with a Super Takumar 135mm F2.5 M42 lens:
Some of my photos are also taken with this lens on Olympus or Pentax body