How much is one stop?

I am a newbie and trying to learn on an istDS.

What do you do when someone reccommends decreasing or increasing the

exposure by one stop?

One stop is either double or half the light. It can be achieved by doubling/halving the shutter speed or adjusting the f/stop 1 stop (f/5.6 to f/8 for example).

 

You should get a basic photography book or just read up on-line (that's how I started out learning). Everything you want to know is out there...google is your friend.

 

http://www.photo.net/learn/

 

Alan

As said upthread, 1 stop is doubling or halving the light. That makes it a 1 step change on the standard shutter speed (1/125 to 1/250th for example) aperture (f/2.8 to f4 for example) or ISO (100 to 200 for example) progressions. Shutter speed and ISO progress by halving/doubling. Aperture progresses by every alternate value doubling (f/1, f/1.4, f/2, f/2.8, f/4, f/5.6 etc)

As said above, each aperture stop doubles or halves the light. The aperture number refers to the opening DIAMETER, and the light admitted depends on the aperture AREA - so the relationship that controls the exposure is the Inverse of the SQUARE of the aperture number:

 

f/1, f/1.4, f/2, f/2.8, f/4, f/5.6

 

1^2 = 1

 

1.4^2=1.96 ~ 2

 

2^2 = 4

 

2.8^2 = 7,84 ~ 8

 

4^2 = 16

etc

 

so f/4 lets in 1/8 th the amount of light, for a given time exposure, as f1.4, as it has 1/8th of the area of a f/1.4 aperture

 

So, on this basis, going from f/1.4 to f/1.7 is about a half stop: (1.7^2)/(1.4^2) = 1.47 ~ 1.51.

I am beginning to see the light :-)

Chuck,<p>

I would recommend that you invest in the soft-cover, "how-to", book written by

Bahman Farzad that is titled "The Confused Photographer's Guide to On-Camera

Spotmetering." It discusses metering techniques and has many analogies and

illustrations that are easy to read and understand. The neat feature is that it

specifically addresses these features on several specific film and digital cameras

including the Pentax DSLR *istD. Several other popular digital cameras are included

and several film camera makers, including Pentax 645N! It's a cool book and for

$20USD or less via Amazon, you can get a mini-course in spotmetering, zone system,

and a lot of basic exposure info.<p>