how does exposure compensation work?

fguihen · 09-03-2008 10:20pm #1

I know what exposure compensation does, but what im wondering is how does it do it? If you increase the exposure compensation will the camera increase the time the shutter is open , or is processing done in camera to make the image appear brighter?

minikin · 09-03-2008 10:41pm

It adjusts the settings prior to exposure (to increase or reduce the amount of light hitting the sensor/film)
If you're shooting in aperture priority it will apply the adjustment to the shutter speed.
If you're shooting in shutter priority it will apply the adjustment to the aperture value.
If you're shooting in full program mode it will apply to both.

say you're shooting something like a white door, the reflective meter reading will result in underexposure (Say it's 1/125 F11)... so you need to apply (for simplicity sake) one stop of compensation to get a correctly exposed image.

In the case of A.P. the resulting image would be exposed at 1/60 F11
In the case of S.P. the resulting image would be exposed at 1/125 F8
In full program mode the resulting image would be exposed at 1/90 F9.5

h.t.h.

ThOnda · 09-03-2008 10:50pm

Recent shutters are electronically controlled, so they are able to adjust exposure time not only in the whole EV steps (from 1/125 to 1/60) but also in halves or thirds of those steps.
I am not sure how that works in Shutter priority mode, but modern lenses have also "half" stops. Maybe the aperture in lenses could be set even to thirds.

Use Av programme (Aperture priority) and watch the speed setting in your viewfinder if you can handhold it :-)

minikin · 10-03-2008 8:03pm

did that clear things up for you fguihen?

ThOnda · 10-03-2008 8:21pm

I hope he didn't get scared :-)

fguihen · 11-03-2008 9:52am

hi guys. sorry for not replying sooner. Yes, that perfectly clears things up.

After reading your replies i remember doing this very test a year ago wtih my panasonic, and I still had the snaps and exif data to show me the shutter value was changed to adjust the exposure.

Its vital info IMO but is not mentioned in the camera manual. thanks a mil guys.

minikin · 11-03-2008 9:56am

camera manual?... that's that book thing that's wrapped in cellophane, yeah?
makes a great coaster!

Mellor · 11-03-2008 12:49pm

ThOnda wrote: »

I am not sure how that works in Shutter priority mode, but modern lenses have also "half" stops. Maybe the aperture in lenses could be set even to thirds.

Yeah, lens ang shutters both do thirds
http://en.wikipedia.org/wiki/F_stop#Typical_one-third-stop_f-number_scale

If the exposure comp on your camera can comp in third steps, then the shutter speed and f-stop are both in thirds.
This is so that 1/3 comp is available in both AV and TV mode.

how does exposure compensation work?

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