So Im going away for the summer to do trail work (professional for the first time instead of volunteer) and Im bringing along a camera and tripod. I was wondering if I could get some good advice for exposure. I have a hand-held spot meter which I can point around at the sky and the subject to get a good ratio, but I am wondering where I should put my exposure in relation to the brightest and darkest part of my subject. I was thinking about it, and I realize that in constant lighting, objects reach a finite point of complete reflection but as they get darker they continue to lower in stops indefinitely. I guess I also want to know how many stops of light my film can record. I have Kodak T-Max 100 120 and Kodak Portra 160 standard 220. I will mostly be shooting landscapes. Thanks
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The subject you are inquiring about is called "latitude" or "dynamic range" -- the range of illumination which can be recorded by a sensor with some detail, between the limits of total black and total white. For B/W film or color negative film, this range is roughly 8-9 f/stops. For color positive film, this range is much more limited, perhaps around 5-6 f/stops.
Try doing a simple test for yourself -- photograph a uniform or slightly textured surface at your meter reading and also several f/stops above and below, then examine the results. If you do your own printing, print the metered exposure so that it comes out medium gray, then print the other exposures the same, letting them come out brighter and darker. You will then know what to expect when photographing a scene with high dynamic range. If you shoot digital, or if you scan your film and print digital, you can simply read the {R,G,B} or Luminance values directly from the digital files and see how they vary with exposure.
To really understand this subject, reading an Ansel Adams book on the Zone System is highly recommended.