exposure compensation

[Dean Pascoe Williams]

when I set my cameras exposure compensation mode to +1, am I in effect increasing or decreasing film speed

In other words...am I over exposing by 1 stop or under exposing by 1 stop

 

[wiltw]

You are adding 1EV more exposure. It has nothing to do with 'film speed' increase, it is merely compensating for the fact that the reflected light meter is expecting a target with 18% reflectivity, but it is seeing a target with more reflectivity than that (e.g. Caucasian skin) and you are telling the meter that the target is 1EV brighter than it assumes.

 

[John Koehrer]

wiltw is correct, but in effect +1 is the same as reducing the film speed.

 

[wiltw]

A 'film speed increase' effectively changes exposure for ALL shots on that roll of film, not merely some shots & dependent upon subject brightness!
For example, shooting Velvia (ISO 50) at EI40 is changing film speed. Compensating for false subject brightness (deviation from 18% gray) is simply adjusting exposure...a reading with incident light meter would use ISO 100 on the meter for the entire roll, not use EI50 because a bride in white is not an factor for any incident meter! You COMPENSATE reflected light readings, you adjust film speed with incident light readings.

 

[MattKing]

when I set my cameras exposure compensation mode to +1, am I in effect increasing or decreasing film speed

In other words...am I over exposing by 1 stop or under exposing by 1 stop

This will really sound anal, but ...

"Over exposure" means too much exposure. "Under exposure" means too little exposure.

By setting the exposure compensation mode to +1, you are telling the camera to adjust its settings so as to give the film one stop more exposure than what the meter recommends. You do this because you believe that the meter will be fooled by the reflectivity of the subject - the meter will try to make the subject average out on the film as an 18% grey (or a coloured version of same) and you want the subject to average out on the film as what it really is.

 

[removed account4]

hi dean

all that setting does is it allows you to over or under expose your film
without having to "remember to do it". you know how they say, if you are out
photographing in the snow or on the beach &C and you have to add a few stops
of light to compensate for the false reading your camera gives you ...

have fun !
john

 

[Mainecoonmaniac]

You can't really change the speed of your film, but +1 is equivalent to halving the your ASA setting or in other words, doubling the amount of light metered. Some cameras have a bracket setting for "exposure compensation". I have a Canon F-1 that has that setting that overrides the automatic exposure. If I shoot manually and need a +1 compensation, I just half my shutter speed or open up 1 stop. I don't think it will effect the whole roll since you can set it back to the original setting.

 

[tkamiya]

By setting your exposure compensation to +1 you are:

OVER exposing it by one stop.

Same thing as setting ISO dial for film speed to 1/2 of what it was before, ie from 400 to 200
Same thing as slowing your shutter speed, ie. from 1/250 to 1/125 (and leaving your aperture constant)
Same thing as opening your aperture by one stop, ie. from f/4 to f/2.8 (and leaving your shutter speed constant)

 

[Focus No. 9]

By setting your exposure compensation to +1 you are:

OVER exposing it by one stop.

Same thing as setting ISO dial for film speed to 1/2 of what it was before, ie from 400 to 200
Same thing as slowing your shutter speed, ie. from 1/250 to 1/125 (and leaving your aperture constant)
Same thing as opening your aperture by one stop, ie. from f/4 to f/2.8 (and leaving your shutter speed constant)

assuming there are no arguments to what you said...THANK YOU ! i was a gettn confusioned.

 

[lxdude]

tkamiya is correct.


Except for using i.e. ("that is"), instead of e.g. ("for example").

 

[wiltw]

Let us assume a sunny day, and the 'Sunny 16' rule applies...1/100 f/16 at ISO 100.

We pull out our incident light meter, and it also reads at ISO 100, 1/100 f/16...that is the suggested 'correct exposure' for the amount of light which falls on the scene. It is consistent with the Sunny 16 rule of thumb.


We pull out our camera meter (reflected light meter) and point it at the face of a child, and it reads 1/200 f/16. We dial in EC +1 because the child's face is brighter than a 18% gray card by 1EV...we are COMPENSATING for the fact that the object being metered is brighter than 18% gray. We are NOT re-rating the film, we are giving it the correct exposure, 1/100 f/16, for the lighting conditions. We are NOT 'overexposing' or giving MORE THAN the 'proper exposure' for the amount of light on the scene.

Now we turn around and point the camera meter at a bride in a white gown. and it reads 1/400 f/16. We dial in EC +2 because the gown is brighter than a 18% gray card by 2EV...we are COMPENSATING for the fact that the object being metered is much brighter than 18% gray. We are NOT re-rating the film, we are giving it the correct exposure, 1/100 f/16, for the lighting conditions. We are NOT 'overexposing' or giving MORE THAN the 'proper exposure' for the amount of light on the scene.

 

[puptent]

One other thought here. In a scene with a lot of back light, like someone's face with a bright sky and sun behind, moving the exposure compensation to plus one will "brighten" the face by one f-stop(and also the background, of course). If left to the internal meter, the person you were hoping to take a picture of may only have been a silhouette, a shadow with no detail. And it also works the other way, if you think the internal meter will "overexpose" a particular feature that you would rather have correctly exposed; going negative 1 on the compensation dial will reduce the exposere by 1 f-stop. There are a couple of tricks that you can adopt to do the same thing as moving the compensation knob. If you are using the meter for exposure only, that is in manual mode, the swing needle usually indicates proper exposure within a bracket, or a circle. So by experimenting with the built in meter, and your f-stops to get a proper indicated exposure, and comparing where the compensation dial would put your f-stop, you should be able to figure out in your particular meter swing where plus 1 and negative 1 would be in the view finder, for example, top of the bracket (or circle) equals plus one, needle on bottom of bracket (or circle) equals minus one. You don't have to expose film for this experiment. Knowing this will let you make the adjustments "on the fly" Olympus cameras like the OM-1 and 2, have this feature built into their meters. Maybe we should start a thread on f-stops and EI...

 

[puptent]

I duplicated miltw by being soooo slow. This might help in the future, and you may want to make a little cheat sheet. f-stops f/1.2, f/1.4, f/2, f/2.8, f/4, f/5.6/ f/8, f/11, f/16, f/22, and f/32 are "standard" or "full" f-stops. Moving a single f-stop is the same as changing the shutter speed by halving or doubling. f/8 at 1/500 is the "same" exposure as f/16 at 1/250. Each halving or doubling; by moving from 1/250 to 1/500 is also a full stop. There are "half" stops, or "non-standard" stops on most modern lenses, like f/1.8, and more often f/3.5 which can get in the way of quick calculations; just because you've moved the f-stop ring one click may not mean you've adjusted one standard stop. But if you're depending on your built in meter then... If there is a tricky exposure, the backlit face, or something like that, move very close to your subject and take a light reading with the built in meter at close range, then use that exposure for your shot. Or use a concrete surface to set an "over-all" exposure reading. The palm of your hand is about 2 stops lighter than an 18% grey card, which by the way, can be purchased at any photographic outlet for under $10, and often under $5. Now-a-days, gray cards come with a white face so digi people can set white balance. And f-stop, in case you're wondering why f-16 is a different diameter in your telephoto than it is in your wide angle lens, is the relationship of the len's focal length ("f" stop) to it's aperture. For a 50mm lens, f-2 would be 1/2 of the focal length, therefore an aperture of 25mm. An f-stop of f-16, (1/16) for a 50mm lens, would be an aperture of 3.125mm. I hope some of this has been of help. Exposure is what it's all about. I might suggest going to the library, or going on line, and picking up books on the Zone System, which may help explain the relationship of light and time.