Kim Catton
Member
SO
Compose the picture.
Use spotmetering on the dark shadow in which I want some detail.
go down 2-1/2 stops.
Use (matrix 10 point system, which is in my f80?) to make Broad area reading.
Compare the two readings.
say the shadow spot reading is, after stopping: 1/125@f16
The broad area is : 1/180@f16
Use the shadow reading
say the shadow spot reading is, after stopping: 1/125@f16
The broad area is : 1/60@f16
use the Broad area
Did I get it right ?
Compose the picture.
Use spotmetering on the dark shadow in which I want some detail.
go down 2-1/2 stops.
Use (matrix 10 point system, which is in my f80?) to make Broad area reading.
Compare the two readings.
say the shadow spot reading is, after stopping: 1/125@f16
The broad area is : 1/180@f16
Use the shadow reading
say the shadow spot reading is, after stopping: 1/125@f16
The broad area is : 1/60@f16
use the Broad area
Did I get it right ?

Dear Kim,
'Broad area' means the subject you're photographing, from the camera position, with either the camera itself in one of its full-frame-reading modes or a hand-held, non-spot meter.
Reading the sky is wonderfully misleading. A deep blue sky is a tolerable mid-tone; a white sky (I have one outside at the moment) is typically around 4 stops brighter than grass (another tolerable mid-tone).
Now consider a scene with big puffy white clouds in a blue sky (clouds maybe 4 stops brighter than a mid-tone) and a mediaeval arcaded street with the shops 3 or 4 metres back from the street, under the overhang of the building above. Dark areas of the shop-fronts are quite likely to be 4 stops darker than a mid-tone. That's an 8-stop range. The only way to be sure of giving enough exposure, and no more, is to measure the dark areas of the shop-fronts: the darkest areas in which you want texture, in fact.
Yes, you can get the same reading in a number of other ways. A broad-area reading will give you an identical reading, at a given angle and distance from the shops -- but step back, or angle it up towards the puffy white clouds, and it'll recommend less exposure, or step forward, or angle it down, and it'll recommend more. Likewise, an incident-light or grey-card reading will give exactly the same reading -- for a very limited range of positions and angles. With experience, you can learn what those positions and angles are, which is why people get good readings that way, but there's a lot more experience and judgement involved in doing it that way than there is in taking a spot reading of the darkest area in which you want texture and detail.
Until I understood the simple fact that metering for negs is metering for the darkest area in which you want texture and detail, I wasted a lot of time with spot meters and grey cards, which is why I'm a bit evangelical about it now.
It's worth remembering that the first commercially successful spot meter (the SEI Photometer, still highly sought after today) didn't even have a mid-tone index, just shadow (for neg) and highlight (for movie). I'm not sure why they were added to later meters, because they really are of very limited usefulness.
Cheers,
Roger