I'm aware the P25 has some issues in design and therefore cannot do long exposures in the same way as P25+ despite using the same sensor. Heat transfer from battery and LCD I suppose. I'm after a low cost second hand back, and while I'd prefer the P25+ it is hard to come by second hand unlike the P25.
With ISO50, f/11, center filter, early morning the official 32 second limit of the P25 is a little tight. I don't need 30 minutes, but 2 - 4 minutes would be nice.
It looks like the P25 can be powered via the firewire cable, which might resolve some heat issues. Has anyone tested to do longer exposures in this mode?