I've seen your website before, love your work.
30sec exposure sounds about right, I shoot with a canon 5d.
I found that I can use it up to 30 seconds with acceptable noise and flare.
To bad that at f8 in MF you have much more limited DOF. But I guess you can do longer exposures without quality loss?
Can you squeze longer exposures from the sensor? When does noise kick in?
I know P1 says exposures up to one hour, I like to see samples before I believe it :-)
It was 30 seconds at f/8
not the best shot, just testing out the 35.
All of my work is shot at night. Check it out. http://www.ImagesOfNight.com