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I've bought an Sony A55 camera for home use. Recording video is very important for me. Fortunately this camera is very good in video recording. It records 1080 HD and more important than that it does have autofocus during the video recording. If I ignore sound of lens moves for autofocusing there is another problem that I can't ignore with this camera autofocusing. It gets too hot and stops recording video after 5 to 10 minutes then shows an alert saying "camera is overheat, let the camera cools down". This is a known issue. Sony recommend to turn the autofocus off.

So this camera couldn't be my choice, I want a camera with great video recording capabilities. I have to return the camera then. But before that, I want to know what should I buy after I returned this camera? What is the best DSLR photo-camera for recording videos. I want autofocusing while video recording. Please don't recommend me buying a video camera. I don't want to do that.

When I was very happy with the camera I posted this video to Youtube to show off the focusing future!

I also found Canon's autofocusing EOS 5D Mark II too noisy and also out of my price range!

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Prepare yourself to be migrated to AVP. –  Andres Oct 3 '11 at 2:29
    
Also on the issue of noise on the 5D mkII, I'd guess that is largely lens dependent, and less off an issue with an expensive USM lens on the body. Plus in that video it sounds like the normal manually engaged contrast AF any camera has during video playback, not the continuous you are talking about. –  Dreamager Oct 3 '11 at 6:23

4 Answers 4

Here's my lazy answer ;) http://gizmodo.com/5616241/nikon-d3100-the-first-dslr-with-real-video-autofocus

As an addition to that, 1080p and continual video autofocus is not a desired combination, which is why it's a rare thing to find on more professional cameras. 1080p is designed for high quality video, and no actual movie of any kind ever uses autofocus. All properly edited movies are focused manually (with possible assistance of AF) and the each clip in that editing is never usually longer than a minute or two (unless arttistically desired like some scenes in Children of Men).

This is why for those who are serious about making movies, and want to use DSLRs to do it, don't have a large desire for continuous AF and don't mind that there are limits to how long each clip on their camera can be (usually 20 or 30 minutes). It is a purely a feature in desire by the amateur market who just want to video home movies of their kids and the like, and to get a good working one would like be quite an expensive thing to develop, as well s difficult to cool and a huge drain on battery resources, which is why a good one will be hard to come across, and less likely in higher end cameras.

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Unfortunately, the A55 you are unhappy with is the best-performing at video autofocus among digital cameras to date since it uses phase-detect which is not only is faster but does not require back-and-forth movement of the lens to confirm focus, which is disturbing during video.

Yet, technology moves fast so you may not have long to wait:

  • The Alpha SLT-A77 and SLT-A65 will probably at least match the A55 and may not have the same issue. These are due in November.
  • The Nikon 1 V1 & J1 both integrate phase-detection autofocus as well but use a smaller sensor which could in theory generate less heat. Both are due October 20th.

The fixed-lens digital cameras that do autofocus during video are rather good at it despite using Contrast-Detect (other than the Fuji Finepix F300EXR which used Phase-Detect) because they have so much depth-of-field due to their smaller sensor that focus can be much more approximate.

EDIT: By the way, this article about digital camera movies is dated but the table at the end is computed daily so you can find all the cameras that autofocus during video by looking for 'Yes' in the Focus column.

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As @Itai said, your A55 is currently the camera with best AF video.

The article you linked to speaks nothing about turning off auto focus. It's image stabilization they recommend to turn off. You could get a tripod and/or a stabilizer rig to replace it. Or you could even build one yourself.

With stabilization off, recording times seem to be similar that can be expected from other cameras.

Your requirements of

  • high quality
  • auto focus
  • long recording time

seem to be contradictory, because the longer you shoot, the higher are the chances auto focus will focus on wrong subject at one moment and there goes your quality.

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Panasonic GH2 - No brainer! Simply superb video and absolutely no AF noise with the 14-140 lens.

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It's not an SLR, though — but still might make a good alternative. –  mattdm Oct 9 '11 at 14:42

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