It's no use spot metering the highlights, midtones, and shadows and averaging the readings if the resultant average is outside the film's ability to record them, which will invariably happen with slide film., as Mark writes you need to decide which tones are the most important.
I have to disagree a bit. In essence, basing your exposure on important subject matter is exactly right. The problem with averaging several important areas of subject matter, especially with an unforgiving medium like slide film, is that you may end up with none of them being exposed as you like. Yes, averaging works in many cases, but in cases of high contrast, we need to make a better choice.
With black-and-white film, one "pegs" to the shadows. One develops and/or prints to get desired contrast.
For color negative films, the same thing, but with more limitations, applies.
For slide films and B&W reversal films, pegging to the highlights is a good practice for non-portrait scenes. In contrasty situation, the shadows, and to a lesser extent, the lower midtones, may suffer. For portraits, basing exposure on a skin tone is good. In contrasty portraits, then, the highlights and shadows would suffer. The portrait may not be acceptable; softer lighting may be the only solution.
Average meters work well in many situations and are pretty good with films that have lots of exposure latitude. They tend to have a higher failure rate with less-forgiving materials and contrasty scenes. There isn't always "an exposure that protects both the high and low tones." Sometimes you lose them both and end up with the mid-tone somewhere you don't like.
You can only place one value; others fall where they may. It's good to know this and use your meter help you make an informed decision.
So, to the OP I would advise the following: Identify your most important tonality. Evaluate the contrast of the scene. Mentally place your important value and then imagine what will happen with the others. Slide film has about a five-stop range. If you place a highlight, you can see which values will go black easily. If you place a mid-tone, you can imagine what will happen with shadows and highlights equally easily.
For low-contrast scenes, averaging often works really well. I'd use it in many cases. For scenes of higher contrast, I spend a good bit of time deciding where to place what. For landscapes with white water, it's the water: meter it and overexpose two stops. The shadows go black if the scene is too contrasty. There's nothing to do about that. Often, the shot is still acceptable. For a portrait, the skin tones and maybe let the highlights go blank white.
Sometimes the contrast of a scene precludes making a good photograph on slide film. In that case, don't shoot and save yourself the trouble and money.
There are some things you can do to tame the contrast of slide film: pre-exposure often helps, so does fill-flash and reflectors for portraits. For landscapes, waiting for a cloud to partially cover the sun is often gratifying.
Hope this helps,
Absolutely and as you point out the fix required is often a change of lighting, whether artificial or natural.
Originally Posted by Doremus Scudder
I will suggest though that this problem is common to all photographic mediums, the problem with slide film is that the fix has to be applied during the camera exposure because we are going straight-to-final-output. With negatives we can change the scene lighting or we can burn, dodge and manipulate when we print, or both.
This isn't necessarily the case, in fact Dunn and Wakefield essentially puts pegging to the shadows into more of a special-case-use classification in the grand scheme of photography. It's basic advantage being minimizing exposure, which is nothing to sneeze at, but not necessarily a priority for most shooters.
Originally Posted by Doremus Scudder
Personally I no longer peg any exposure to shadows, my choices are always centered on the mid-tones I want to print, shadows and highlights are simply allowed to fall around that come what may. I will on occasion use a high tone and an offset to peg my mid-tone. I avoid using shadows as a peg because I find judging them unreliable.
Onward, I'm not understanding what extra limits you see with color negatives, can you elaborate.
Your sunset on the lake shot (posted on DPUG) looks great. If you wanted to have detail in the foreground, then you might try to find a Neutral Density Graduated Filter. Galen Rowell used these for exactly the problem you posed. If you can find his filters or similar, you can have both the skies and the foreground details too.
You guys are all wrong!
Average speed is Total distance divided by Total time.
I simply cannot resist. . .
I really don't want to say how one should use the meter and arrive at the exposure he/she wants. I simply first show the OP how to calculate the average of several spot readings in the fashion that a meter with that function would do. I don't say it's a good or bad approach. I did make a comment that if you average a lot of readings then you come up with the same reading as if you use a wide angle averaging meter instead of a spot meter.
I was probably reading to quickly and to quick on my comment, no offense meant to you or Bill.
Originally Posted by Chan Tran
Gladly Mark ;)
Originally Posted by markbarendt
My observation that color negative film has more limitations is simply that color film cannot be developed to such different extremes as black-and-white negatives; no N+2 or N-4 for color negs without a lot of color crossover. Plus, there are no variable contrast color papers I am aware of to help deal with contrast at the printing stage. There are digital (gasp) possibilities but...
As for pegging shadows: we Zonies grew up on shadow-value placement; I feel fairly confident placing shadow values. However, when shooting roll film, I use a mid-tone as well for the most part. The only real danger when using an average value is in very contrasty situations, when the shadows can end up severely underexposed. Highlights will be hot as well, but that is not an issue with most black-and-white films; color is a different matter again. When shooting black-and-white with average readings in contrasty situations, I'll usually give an extra stop exposure to hold some shadow detail and then deal with the overexposed neg at the printing stage.
Thanks Doremus, very reasonable thoughts.
One thing that C-41 taught me about myself/my work, is that "normal" development works well for me.
I have brought that thought back to my B&W work and found it works just fine for me there too. My development target is to get the general "snappiness" I want, especially across the mid-tones. I find almost without exception that I prefer the result when I burn and dodge versus applying plus or minus development to a film, or a change of paper grade.
I give up fitting a scene to the paper in exchange for contrast consistency. Just a different priority.
And if direction is involved, it's velocity not speed as speed is a scalar quantity rather than a vector quantity.
Originally Posted by dehk