Can someone explain what the various ISO ratings of a digital camera really mean? I hear quite often that you can create say ISO 3200 by shooting with a -2 exposure compensation setting. Is it really the same thing? Just looking for some good education! Thanks in advance to all contributors!
The last link was the geeky tech stuff, and does explain ISO..
for the rest of us:
It is a standard that allows us to go understand relationships between different elements of photographic controls.
ISO (ASA in old school terms), is a rating that lets us know how sensitive film/sensor is to light. Higher number are more sensitive and require less exposure, the trade off is more grain/noise.
It is the same ratio as f/stops and Shutter speeds.
ISO 100/200/400/800 In 1 stop increments
(because 1 stop is the accepted term... it really is 1/stop in one direction, or 1/2 stop in the other direction)
ISO 100/125/160/200/250/320/400/500/640/800 in 1/3 stop increments
f/stops f2 f/2.8 f/4 f/5.6 f/8 in 1 stop increments
f/stops f/2.8 f/3.2 f/3.5 f/4.5 f/5 f/5.6 in 1/3 stop increments
Shutter Speeds 1 1/2 1/4 1/8 1/15 1/30 1/60 1/125 1/250 in 1 stop increments
Shutter Speeds 1/20 1/25 1/30 1/40 1/50 1/60 1/80 1/100 in 1/3 stops increments
Now, each progression wither in full stops or 1/3 stops (going higher) will either 1/2 the exposure or 1/3 the exposure from the
former setting. Wither it is ISO, f/stops or Shutter speeds
NOW, Just adding to the EV setting to a WILL technically give you a higher ISO, BUT, It will be underexposed without in camera correction (Push Processing the JPG/RAW file), So, unless you shoot RAW, you probably won't have a usable file. and, even then, 2 stops underexposure will give a very dark JPG, and RAW. But, you may (May) be able to recover the RAW to a normal file.. but, you may also loose a lot of the shadows, since, they (the shadows) were exposed 2 stops under also.
With Film... you have to change (Increase) the developer time to compensate for underexposure (the phrase "expose for the highlights, develop for the shadows") means, you slightly under expose to hold Highlight detail, and over develop to bring up the shadows. Same holds true for digital film.
Cameras that have a "extended" range ISO (3200 or 6400) add an in camera "Push Processing" algorithm to help retain the shadow. Shoot RAW in any case.
Hope This helps a little