Go Back   Steve's Digicams Forums > Digital Cameras (Point and Shoot) > Panasonic / Leica

Reply
 
Thread Tools Search this Thread
Old Apr 9, 2010, 8:46 AM   #1
Senior Member
 
Chris0383's Avatar
 
Join Date: Mar 2010
Location: Southern Connecticut
Posts: 254
Default Waht is the Mechanism for Exposure Compensation

I always thought a camera uses ISO, Shutter Speed, or Aperture to control exposure.

Given that all three variables are set supposedly properly, the manual tells you to revert to exposure control to get the right amount of light if the light still isn't proper.

So what mechanism does the camera use to introduce a forth variable (Exposure Control) to get the right amount of light. Is it redundant where actually tweaking of the other 3 variables properly can bypass the need for exposure control? Is exposure control like increasing gamma using post processing software ?
Chris0383 is offline   Reply With Quote
Sponsored Links
Old Apr 9, 2010, 8:59 AM   #2
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

Quote:
I always thought a camera uses ISO, Shutter Speed, or Aperture to control exposure
That's correct.

As long as the ISO speed is set to a specific speed, it should be varying either the Aperture or the Shutter speed if you're referring to using Exposure Compensation with a + or - EV setting.

If you're in Av (Aperture Value, a.k.a., Aperture Priority) mode, when you spin the control dial, you're changing the Aperture Value (expressed as f/stop). When you vary the aperture, you're controlling the iris in the lens (which like a pupil in your eye, can be opened up to let in more light or closed down to let less light in). When you use Av mode, you select the desired aperture. Then, the camera selects the correct shutter speed for proper exposure, based on how it's metering the scene.

If the camera is metering the scene where you end up with a darker or brighter exposure than desired, you can use Exposure Compensation to change it's behavior.

If you use a -EV setting (needle to the left of center) with Exposure Compensation while shooting in Aperture Priority mode, you'll have a darker exposure than the camera would have used. It gives you a darker exposure by using a faster shutter speed with the selected Aperture. If you use a +EV setting (needle to the right of center), you'll have a brighter exposure than the camera would have used. It gives you a brighter exposure by using a slower shutter speed with the selected Aperture.

If you go to Shutter Priority (where you select the Shutter Speed and the camera selects the Aperture needed), it does the same thing (brighter or darker exposure with Exposure Compensation) by varying the Aperture instead. If you shoot in Programmed Auto, it may vary either one (or both) to change the exposure.

If you're using manual exposure, there is no Exposure Compensation. You're controlling the variables by setting the Aperture and Shutter speed (using the meter as a guide, with the needle to the left of center giving you a darker exposure, and the needle to the right of center giving you a brighter exposure, as compared to the way the camera metered the scene).

The selected Aperture impacts the shutter speeds you'll need for proper exposure. For example, an aperture setting of f/2.8 (if you're using a brighter lens with that aperture available) will allow you to use shutter speeds 4 times as fast as one as you could use at f/5.6 for a given lighting condition and ISO Speed. Aperture also impacts Depth of Field (wider apertures will allow for a shallower depth of field when desired to help subjects stand out from distracting backgrounds).

The aperture scale in one stop increments (with larger than f/1 apertures possible but very rare in lenses) goes f/1.0, f/1.4, f/2.0, f/2.8, f/4.0, f/5.6, f/8.0, f/11, f/16, f/22... With each one stop move to a smaller aperture (represented by higher f/stop numbers), you will need shutter speeds twice as long for proper exposure for the same lighting and ISO speed (only half the light gets through compared to a one stop larger aperture).

There are only 4 main variables involved for proper exposure. We've already discussed Aperture. The other variables are Lighting (typically measured in EV, which stands for Exposure Value), ISO speed and Shutter speed.

ISO speed is how sensitive the film or sensor is to light and is the same thing as the older ASA rating for film. The higher the ISO speed, the faster you can expose it (each time you double the ISO speed, you can use shutter speeds twice as fast for the same lighting and aperture.

Shutter Speed is how long the camera's shutter stays open to expose the film or sensor.

IOW, it all boils down to how much light you have, how sensitive the film or sensor is to light (which you control via the ISO speed), and how much light you need to let it see to "expose" the image (which you control via the aperture opening size and shutter speed).

Exposure compensation is just a tool that makes it easier to vary your exposure while still taking advantage of other auto type features, without the need to resort to setting both aperture and shutter speed manually in changing lighting.
JimC is offline   Reply With Quote
Old Apr 9, 2010, 1:04 PM   #3
Senior Member
 
Chris0383's Avatar
 
Join Date: Mar 2010
Location: Southern Connecticut
Posts: 254
Default

Excellent explanation JimC. It is important as there are times we want a certain aperture for a certain depth of field or shutter speed to capture or freeze action all the while keeping the noise down or being satisfied with more noise.
And it is good to know which variable will be altered when using EV.

Thanks for taking time to give that great EV lesson to a newbie Jim.

That was excellent.

Last edited by Chris0383; Apr 9, 2010 at 1:07 PM.
Chris0383 is offline   Reply With Quote
Old Apr 9, 2010, 2:18 PM   #4
Senior Member
 
Join Date: Jan 2010
Location: South Africa
Posts: 233
Default

That's a good post from Jim: One to be printed and kept.

I shoot most of the time with my FZ38/35 set to -1/3 EV.
I find this a necessary adjustment, and have read a number
of similar opinions posted by FZ28 owners too.
dbnnet is offline   Reply With Quote
Old Apr 9, 2010, 2:31 PM   #5
Senior Member
 
Chris0383's Avatar
 
Join Date: Mar 2010
Location: Southern Connecticut
Posts: 254
Default

dbnnet;

do you have a preferable mode you use most often. I read that most photographers us Aperture mode; but once you acquire a good camera like the FZ35, I believe one has to be more flexible with the modes they use to get the most out of such a feature rich camera.
Chris0383 is offline   Reply With Quote
Old Apr 9, 2010, 2:54 PM   #6
Senior Member
 
Join Date: Jan 2010
Location: South Africa
Posts: 233
Default

Chris, there is a trend amongst a number of us here on this Forum.... but please tread with caution Remember that these are ALWAYS personal and specific to ones own preference and likes!
But I would say that "P" mode is the most advantageous mode for a number of reasons, but the most important being that the iA mode will not really provide you with the greatest results that are possible with such a versatile camera. A mode has its place too, i.e. if one wants to shoot fast moving objects and fix the aperture as open as possible. M mode has its place for long exposures (the FZ38/35 can handle up to 60 seconds).

Many people here have debated about other preferences and settings: There are also a number of us who set Sharpness and Saturation at +1. But its all about ones own preference i.e. I find my flash to be too bold, producing ghost looking images when filming people.... so have mine permanently set to -1/3. There are others here to do the exact opposite.
Regards
dbnnet is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 4:23 PM.