Mike,

A back-of-the envelope rough calculation of the maximum size of Mars at its closest in a couple of days:

maximum diameter about 20 seconds of arc, or .0055 degrees

angle of view of a 500mm lens = about 4.125 degrees on the long axis of a 35mm frame

So on 35mm film with a 500mm lens, you can get about 645 Mars diameters along the 36mm dimension, giving a size of about .0558 millimeters for the diameter of Mars on the film.

In other words, Mars is small, even if it appears bright, and you'll need special equipment to get it to appear large enough for a perspective on size. Even with enough focal length, capturing a moment of still air with good enough "seeing" for detail on the planet is very elusive, and one of the reasons professional observatories are built on high mountains with still local pools of air.

For a wider angle view with distinctive Mars and star colors (i.e. reasonable expectations for your situation), shoot with a barn door drive, a Fuji 400 ISO print film or Elite Chrome 200, and bracket your exposure times widely. A well aligned barn door drive can give you a few minutes of good tracking with a 135mm or shorter lens, and a really well aligned drive (experience and knowledge required) with no tangent error will get you up to 180mm to 300mm for up to 15 minutes or so.

You should also be able to get star trails for Mars and surrounding bright stars (such as the Pleiades and Hyades) with either of the above films and a fixed tripod. Bracket your exposures. Colors will show here as well.

Lee