- Reports of the 7D overheating seem to be more prevalent than they were/are for the 5D, though there have been reports of the 5D overheating, so it's not entirely unique to the 7D.
- The camera continues to operate (most of the time) with the thermal warning on, and most people don’t really notice a degradation in the image quality, though one user reported a glowing pixel in the dark areas of later footage.
- Most people are encountering the problem after an extended period of operation (i.e. into the second hour of non-stop usage.)
- Some cameras seem to display the warning earlier than others (though it’s unclear whether this is due to differences in operation, or actual differences in the way cameras are calibrated.)
Here’s some current theories:
- Shooting 720p generates more heat than 1080
The Theory: Unlike the 5D Mark II, the 7D has two processors instead of one, and also supports 720p while the 5D Mark II (at the moment) does not.
The Proof: The first couple of people to report overheating were both using 720p, and one of them subsequently did an experiment switching to 1080p, and reported that the camera didn’t overheat after a similar period of operation.
Conclusion: Since then, there’s been a number of reports of overheating in 1080p, so it may be a contributing factor, but clearly isn’t the only one.
- Don’t hand-hold the camera
The Theory: your hands cause more heat to build up within the body.
The Solution: use on a tripod or other kind of rig.
Conclusion: None. One person claimed he had it happen as soon as he went to hand holding, while another person has had it occur both while on a tripod and holding it in the hand after 1-2 hours of use.
- Place an ice-pack on the camera on the right side of the LCD
The Theory: reduce the internal temperature with external cooling.
The Proof: not a lot of people have documented doing this.
My Take: I’d be wary of the possible damage to the device by introducing a really cold object to part of the camera body. Using some kid of cooling around the body may make sense, but getting the right amount in the right place might be both difficult and cumbersome.
- Use a large L lens
The Theory: Canon’s L lenses contain a lot of metal, making for a large heat sink. Cheaper lenses are often all plastic, other than the mount, so won't "absorb" much heat.
The Proof: one poster (see below) suggested this because after getting the temperature warning he switched to a large L lens and noticed the warning went away.
My Take: without knowing where the heat is being generated, it’s difficult to know how it would get “transferred” to the lens. Clearly, the heat source isn’t right next to where the lens is connected (since that’s where the mirror box is!) so it’s not obvious to me how efficient the cooling would be; but maybe every little bit helps.
- Don't use a cover over the LCD panel
The Theory: The Z-Finder (an optical device used to help with viewing the screen that covers the LCD) is “trapping” the heat from the LCD display, or not allowing proper cooling.
The Proof: One person said he’d got the warning with the Z-Finder on, but after removing it, the warning went away, but another person said he had it come on without the Z-Finder, and it's clearly happening to users who aren't using one.
Conclusion: It's hard to tell if this really makes a difference, though if you’re on the edge, - as has already been said - every little bit may help!
Meanwhile Ole Jørgen Liodden, at Canon Field Reviews, reports that he took a 7D to Antarctica, and found it performed very well. He probably didn’t have any problems with overheating… 7D #1 Weather Sealing
One interesting note:
Some 5D Mark II users who use the battery grip have reported some problems with water leaking between the camera and battery grip. The battery grip for 7D is new and seems tighter and better sealed. In my case the 7D had absolutely NO problems with snow, rain and water (sea spray).
Also - for what it's worth - he had no problems with a 5D Mark II he had with him, which is a bit of a surprise. Earlier this year there was a report of a photography expedition (which maybe wasn’t quite as hard core as Liodden’s seemed to be, but it was still pretty extreme) and the users of the 5D’s suffered a fair number of failures.
The largest group of failures through were among the Canon 5D MKIIs. Of the 26 samples of this camera onboard, one quarter (six) failed at one time or another, and while three recovered, the other three never did.
- Luminous Landscape: Antarctica 2009
[UPDATE 12/17] One thing that might not be clear to those that have not been closely following this issue: all the reports of over-heating relate to long periods of continuous video shooting, and usually don't appear until the second hour of usage. If you're shooting stills, or shooting short video sequences (say one or two four-five minute sequences) then you should have no problems with over-heating