Thanks guys. Here's the photo that I was working on:
It's a digital photo. I was shooting with Dan Newton (liquidinplastic.com). He has instructions for stacking startrails with a digital camera. I liked it but I'm still a film junkie. Before I started the digital photo which consistes of over a hundred 30 second exposures, I set up the medium format with VS100 film. I also set up the 4X5.
The nice thing about VS100 is that the reciprocity starts to kick in and sort of self regulate the exposure. I just focused, set the aperture to f16 and opened the shutter.