Reading a book now I have a question

[rickp1]

A little while back I was having some issues with exposure so after some research and recommendations I picket up the book called "Understanding Exposure" by Bryan Peterson.

I'm still a bit unsure about how I feel about the book. In the beginning of the book he talks about the 3 items needed to achieve a correct or creative exposure, shutter speed, aperture and ISO.

As I was reading about each topic I noticed that during his explanations and descriptions of each image all he really described was shutter speed and aperture used and leaving out ISO. At the beginning of the book he talks about ISO and what it is but after that he doesn't mention what ISO he used to compose his shots.
I thought the lack of this information in each instance was a real void in understanding how things tied into each other. Especially for a newbie.

Anyway, one of the questions I have is in the book he makes reference (more than once) of getting his exposure by metering the sky, then recomposing. Is that a normal technique or am I missing something. He never explains in the book.

Thanks
R.

[RichardTaylor]

I think that book was basically written in the days of film where you didn't have the huge control over the ISO (ASA) that we have today.
I don't have my copy as I lent it to my sister.

Once you loaded your camera that basically was it, especially for amateur photographers. If you were shooting slides it was Kodachrome (25 ASA when I started) or high speed Etachrome (ASA 160 from memory), which you only used when absolutely necessary.
For B&W Tri-X was considered fast (ASA 400)

AS far as metering the sky goes I mostly use it for sunsets.

Example from our front yard from a couple of years ago.

Canon 350D (Rebel XT) with Canon 70-300 IS lens @ 70mm
ISO 200 1/100 @ F6.3 .Hand held. Manual exposure.

Here I metered the sky and recomposed. If I would have metered the whole scene, especially if using matrix/evaluative/area metering, the dark trees exposure reading would have have made the sky a lot lighter.

(2) Here there are two problems, the bright sun and the dark trees.
Metering the sky helped solve the problem along with some exposure compensation. This was part of a series where I was trying different exposures.

Camera: Canon EOS 40D
Exposure: 0.003 sec (1/400)
Aperture: f/20
Focal Length: 150 mm
ISO Speed: 200
Exposure Bias: -2 EV

[JAD40]

If you meter for a sky that is brighter than your subject then your subject will be underexposed. It will most likely lead to a silhouette type photograph.