This site is moderately light-polluted, and I find that photos made without a light pollution filter get overexposed at 40 to 50 minutes at f4.5 or 6. I have not yet quantitated the background fog density. I also have a handy home-made eyepiece holder on the pier. My cameras include a 35 mm Nikon FM2N and a Pentax II 6x7 medium format camera. I have just begun to use the Pentax and do not yet have a scanner capable of better than 1200 ppi on medium format film, so experience to date is very limited.
All film is processed by a local processing specialist shop.
These people use machines rather than dip and dunk processing but are knowledgeable and cooperative about the needs of astrophotographers. Because of the lack of clear image boundaries on astro negative strips I often have to move the image selection box around to cover all of the negative. I then do a final scan into a directory named for the date of the photo session. If it looks promising, I use the Levels or Curves sliders to improve the color balance and contrast as much as possible without washing out highlights or increasing grain excessively. I try to avoid letting the sky go to jet black, following the advice of Jerry Lodrigus and Chuck Vaughn and try to keep it at a level of 10 to 20.