I work for JVC and would like to help. Your post is a good one.
The GZ-HM550 does have good low light performance, and has an auto focus that is considered to be very good.
Having said that, you are describing situations that are tricky for virtually any camcorder. Night time, low light video with bright objects in the picture is difficult to record correctly. Particularly scenes with rapid changes in brightness, which can trick any focus or exposure system. Luckily, there is a pretty easy solution.
JVC customer care was correct in suggesting you try the manual modes. Specifically I would suggest turning off the auto focus, and setting/locking the focus on infinity (far away). I believe that will solve most of your concerns. The night mode is also worth trying to see if you get more consistent color and exposure, although the auto mode may work fine once the focus is locked.
Please try this, and let me know if it helps.
I recently purchased (09/09/2010) the JVC GZ-HM550 camcorder, mostly for use at Disneyland for recording the rides and shows. This camera has been rated very well for it's low-light performance and it's autofocus. However, the camcorder kept having problems keeping focused (in dark situations), whether I was moving on a ride or standing watching a show. I also had problems recording the fireworks (every time a shell would explode, the camcorder would loose focus).
I tried contacting JVC about this, but was met with the most basic of solutions (specifically: "we would recommend that you activate the image stabilizer on your camcorder and that you try using the SCENE SELECT options in the camcorder?s menu (when the camcorder is in Manual mode) to determine if this helps your camcorder remain focused" and "try adjusting the settings in manual mode").
Granted, how are they to know if I know to try these different features on my own? I'm not completely inexperienced with these sorts of things, for the record. I OF COURSE had my image stabilizer on at ALL times and tried the different modes available to me (which aren't many). When I used the "Night" mode, focusing seemed better, but the image was MUCH MUCH darker (not to mention it didn't capture colors correctly in this mode). So that's no good, for what I need this camcorder for. The other modes did me no good, either. The only other option left, really, is that I need to decrease the shutter speed, but by doing that there's a lot more motion blur (which, again, doesn't help me out).
This is typically a $799 camcorder (I got it on Amazon for $472). If I had paid full price, I would be even more upset than I already am. Even so, I'm concerned that I'm having a problem with a feature that is flaunted around as being so great, and on a higher-end model no less, when it isn't working so great for me.
What I'm hoping is that this is just a defect with this particular unit, because I love everything else about it.
If I end up returning it (I still have a little under two weeks to do so), are there any other models that you all would recommend for my situation? I've seen other comparable models out there, but their image sensors are roughly half as big (mine- 1/2.33", theirs- 1/4"). At the same time, though, their maximum aperture is around F1.8, as opposed to my JVC's F2.8. Do you think the larger apertures would make up for the smaller sensors?
I REALLY appreciate any and all help you all can provide me with. If it seems that I just need to return this unit and look for a different model, then please tell me so (and again- with some suggestions).
P.S. For reference, here's CNET's page with the Specs for my camcorder: http://reviews.cnet.com/digital-camcorders/jvc-everio-gz-hm550/4507-6500_7-33949106.html?tag=specs.