ISO vs Exposure Compensation

[astroNikon]

ISO vs Exposure Compensation

Which one would you use in what situation ?

I'm thinking they are kinda they same, except maybe EC allow smaller corrections in exposure control. And maybe it doesn't introduce noise.

 

[Warhorse]

ISO if you can not/do not want to change shutter/aperture combination.

 

[Overread]

They are very different things;

Photographic Exposure is defined by your aperture, shutter speed and ISO.

That's it - NOTHING else contributes to the final exposure that you get in the camera. If you are working with JPEGs then there are auto-edit settings that you can define that will tweak the final result, but that's only tweaking it the same as if you had a RAW and edited it in editing software.


Exposure compensation works in any mode that is semi or full auto. What it does is takes the cameras meter reading; but then under or over exposes the shot based upon the meter reading. The camera does this by changing its controlled setting(s) to allow this.

So for example if you are in shutter priority mode

Base reading gives you f4, 1/200sec, ISO 200

So you the photographer have set the shutter speed of 1/200sec and the ISO of 200. The camera then sets the value of the aperture at f4.

However if you then set exposure compensation to overexpose by 1 stop (+1) then you'd get:

f2.8, 1/200sec, ISO 200

Because the camera has taken the same meter reading from the light present; but then opened up the aperture by one stop - creating an "overexposure" based upon the meter reading of one stop.




Now in Nikon cameras you can use exposure compensation in manual mode; however here all it does is change the value of the middle point on the meter that is displayed. This allows you to continue to get the needle "in the middle" whilst at the same time over or under expose the shot by the amount you've selected (remember in manual you'll have to change the settings to get the effect).



Exposure compensation is thus not part of the actual exposure, its just a bias on the exposure that changes the setting that the camera uses

 

[Derrel]

"Sort of depends on how you view things!" Here is how I look at it.

ISO sets the default level of noise,resolution ability, dynamic range, and color richness. At base ISO levels, all digital cameras have their lowest noise, richest color, widest dynamic range, and their highest resolution capabilities. For example, the modern Nikons have 13.7 to 14 or so stops of dynamic range at BASE ISO value, and then as the ISO is raised, the dynamic range drops off, more and more and more. And so does the color depth: the wonderful, rich color rendering of ISO 100 declines to a pastel, watercolor painting-like mess at ISO 25,600. Resolving ability drops off markedly as the ISO's reach the highest possible values. So....the ISO determines what total compromises you are willing to live with, in exchange for the "ballpark settings" you need for a situation. In bright light, I normally set a lowish ISO; not always the lowest. In crappy light, I usually elevate my ISO to 800 to 1600.

Exposure Compensation (EC) is a way to get the LIGHT METERING's results in line with the desired exposure result. Exposure compensation is a way to "compensate the exposure" the light metering is giving, so that the desired subject is exposed the way the photographer wants it to be exposed. Exposure compensation is a well-known control to get the right exposure by biasing the metering system to favor over- or under-exposure, and can be used at any and all ISO setting the photographer has chosen to set, or which will be applied in AUTO-ISO situations. In many situations, Exposure Comp helps when the background is very bright, or very dark. A classic example: theatre productions where a spot-lighted actor is in front of a huge expanse of a dark, dimly-lighted background. One can spot meter, but it is also possible to set the exposure broadly at say, Minus 5.0 EV of EC, and get a good exposure using Center-weighted metering. In portraits, a person standing in front of dark, green foliage might very well benefit from Minus 1.7 EV EC if the shot is a full-length shot done with a 50mm lens from 15 feet back. A black dog on a snowy patch needs Minus 2.5 or so. Blacks need MINUS many times, white tones often need PLUS exposure compensation dialed in.

A great example: FOGGY DAYS. You almost always need to add at minimum, 1.0 to 1.5 EV of EC on foggy days, to make the scene look light and white, not grayish. One thing to keep in mind: Nikons, and newer Canons with color-aware light metering tend to "recognize" situations like foggy weather much more so than color-blind, "dumb" light meters from days of old, so that in my experience, the "intelligent" light meters that d-slrs have is not like a dumb, old Sekonic which meters everything so that the exposure is a baseline 18% reading.

Nikon cameras also offer a third option, exposure fine-tuning, which is NOT indicated in the viewfinder, and allows the photographer to deliberately create a semi-permanent, user-defined degree of exposure offset, so that the Zero'd Out or "dead On" exposure reading is in line with the shooter's opinion as to what a proper exposure ought to be, or to compensate for systemic errors, such as say, a lens that habitually under- or over-exposes, such as can happen when the diaphragm is wonky, or on zoom lenses that have a low T-stop due to loss of actual light transmission, etc.

 

[TCampbell]

That's it - NOTHING else contributes to the final exposure that you get in the camera.

...and lighting. Everyone seems to leave that off. It seems to be left off so often that people forget that it's an option to change an exposure by changing lighting.

In the "good 'ol days" when we were stuck with whatever film speed was loaded in the camera and couldn't change ISO and were already at the lowest f-stop and slowest shutter speed we dared use for the shot... lighting was the ONLY way left to alter the exposure.

Here on TPF, we frequently read posts by a person struggling to get the indoor low-light shot of their children who won't sit still and I think..... great... take them over near the window for the shot. When I did weddings... I almost never walked into a room without re-arranging the furniture to sit the models in such a way as to take advantage of the light from the windows.

But I digress.... everything else you say is spot on.

In a nutshell... exposure compensation is used when you don't want to use the exposure that the camera's light meter suggests using (especially in a semi-auto or program mode where the camera will control part of the exposure settings for you.) You might recognize the light meter is mis-reading the information (which it will do if the subject is mostly "black" or mostly "white" because these alter the reflectivity of the light and fool the meter.)

 

[Overread]

TC very true lighting in itself can be changed to change the exposure. Although I suspect it oft gets left off because most of the people we talk to here are at the first stage of learning - that of getting a hold on teh camera itself.

I think that its easier to work with if they use ambient lighting and learn to work the camera first; then once they've got that really understood they can move to the idea of directly manipulating the light that they are working with (in small ways with reflectors up to big ways with maybe multiple flash units).

 

[TCampbell]

TC very true lighting in itself can be changed to change the exposure. Although I suspect it oft gets left off because most of the people we talk to here are at the first stage of learning - that of getting a hold on teh camera itself.

I think that its easier to work with if they use ambient lighting and learn to work the camera first; then once they've got that really understood they can move to the idea of directly manipulating the light that they are working with (in small ways with reflectors up to big ways with maybe multiple flash units).

I agree... lighting isn't just "light"... it's shadows, directionality, lighting modifiers, light power, distance from subject, and angles of incidence & reflection (and we haven't even got to the color gels yet). Lighting opens up a whole new chapter of creativity and fun -- but I completely understand why it's probably not a good idea to flood beginners with that much information until they can at least grasp the relationships between aperture, shutter, and ISO.