I started as an EOS3 user and the limited 30 second maximum aperture priority AE duration was an annoyance. Not knowing any better, I assumed all these aperture priority AE types were all limited until I read about the Olympus OM4 and Pentax LX and found in their technical specifications that they can go 240 and 125 seconds respectively. After I acquired both, I found out that the OM4's 4 minute limit is hard coded while the LX will go on for as long as it takes to properly expose the scene - while monitoring it in real time and changing accordingly, or the batteries are depleted. Certainly a good argument for not strictly relying on the spec sheets!
Originally Posted by fstop
BTW, if this is an important function to anyone, I tested the maximum aperture priority AE durations on numerous cameras and found that only the Pentax LX can do this but let me know if you are aware of any other. I have 3 LX bodies and all three have been tested to expose the same duration up to an hour given the same exposure but I have conducted individual tests with >2 hour durations. I also found all the Canon's I tested have the 30 second limit and most all other brands and models vary unpredictably but typically not dependable past a few minutes.