ISO Vs. Exposure Compensation

[Travis]

Can someone please help me with principal differences between ISO and Exp Comp and how they should be applied?

I am aware of little tips (ie. Increase ISO when shooting indoors low light, or increase exp comp when shooting snowy scenes), but I don't really understand why.

I know that ISO increases the sensitivity of the image sensor, but isn't that what Exp Comp does too?

Thanks for any help

[Marko]

ISO fiddling and exposure compensation can be used to accomplish the same task. All exposure compensation does is make the scene brighter or darker relative to the camera meter's exposure setting. ISO - shutter speed - and aperture are all directly related in a linear fashion.

Let's say the meter reading says F4 at 1/60 and you are shooting at ISO 200 in manual mode.

Then setting the ISO to 400 is the same as plus 1 stop exposure compensation. You can do either and get the same result.

Due to the fact that higher ISO can introduce more noise, I use exposure compensation instead. As far as I know depending on what camera you have, at the end of the day exposure compensation works by manipulating the shutter speed or the aperture.
So again F4 at 1/60 at ISO 200.
Make that shutter speed 1/125 and it's identical to minus 1 exposure compensation. OR make the ISO 100 F4 at 1/60 and accomplish the same thing. OR make the F-stop F5.6 1/60 ISO 200 to accomplish the same thing.

Does that make sense?

thx
marko

[Travis]

uhhhh.... kinda... but not really....

for instance.... if ISO causes grain or noise... why do we even bother increasing it? why don't we always leave ISO at 100 and use exp comp to adjust sensor sensitivity?

thx

[Marko]

for instance.... if ISO causes grain or noise... why do we even bother increasing it? why don't we always leave ISO at 100 and use exp comp to adjust sensor sensitivity?

Firstly - The noise level on many cameras is acceptable until about ISO 800 - then you may (depending on camera) start to notice noise...more so in enlargements than small 4x6 prints or images for the web.

When you are shooting a still life your logic makes good sense. And in that case I would adjust the shutter speed OR play with exposure compensation since aperture choice also gives you depth of field choice (the level of sharpness between the forground and background in your image) ...and most photographers think that variable is the key to the majority of their shots.

However when shooting a person, a person cannot usually stay still at shutter speeds slower that 1/60 EVEN IF THE PHOTOGRAPHER's camera is on a tripod.
So if the shutter speed must be 1/60 or faster and you want to select your aperture...the only other alternative is to manipulate the ISO.

So it really depends on WHAT you are shooting....and again please ask more questions if this is not clear.

thx
Marko

[Travis]

I guess to kind of add to this....

I just started moving into using my D60 in full manual mode and noticed that exposure compensation control is disabled....

funny because I actually found this out through experiment.... I was taking some snow pictures in manual and was adjusting e.c. upward to whiten the snow.... when i got to +5ev and the picture looked the same I thought something was wrong with my camera.... I confirmed via the product manual the e.c. is disabled in "M" mode... it's a little misleading on the Nikon D60 because the menu allows you to make a e.c. adjustment but doesn't do anything. I would have preferred it to grey out the e.c. adjustment area in manual mode. I guess this is common in most DSLR's??

I also found out that ISO adjustment amplifies the sensor where as exp comp actually changes the shutter/aperture settings??? So if you are in a semi program mode with altered exp comp the display settings for shutter/aperture aren't actually accurate??? <--please correct me if i'm wrong

I was under the impression that most of the prosumer and professional photographers shoot exclusively in "M" mode..... but a lot of the technical advice I am reading on this forum mention exp compensation adjustments under certain shooting scenario's... so this leads me to believe that prosumers/professionals also use semi-automatic "P" and "A" modes too?

thank you

[tegan]

I would not say that most pro photographers shoot in M. mode but we do watch the settings very carefully and know how they influence lens sharpness, depth of field, background brightness, colour rendition, etc. We change modes to get the reults we want.

Tegan

[Marko]

So if you are in a semi program mode with altered exp comp the display settings for shutter/aperture aren't actually accurate??? <--please correct me if i'm wrong

I believe this is correct. It will say for example F4 at 1/60 but if you have added exposure compensation into the mix it will STILL say F4 at 1/60. So be careful when you change scenes. (it should tell you in another small window what the exposure compensation is...but the main exposure will look as it did before you added the E.C.)

I would say that both aperture priority and shutter priority are OFTEN used by pros when the situation calls for it (like at a racecar event where you would want shutter priority - or shooting a scene with changing lighting where you WANT a certain aperture)

[tegan]

I am not sure what you mean by semi-program mode but generally if you add in exposure compensation plus or minus, it DOES show up as a different fstop or shutterspeed in the information provided in the viewfinder and on the LCD screen.

Tegan

[Travis]

semi-program as in aperture priority or shutter priority

[Marko]

I am not sure what you mean by semi-program mode but generally if you add in exposure compensation plus or minus, it DOES show up as a different fstop or shutterspeed in the information provided in the viewfinder and on the LCD screen.

I guess it depends on the camera then since I have worked with both Nikons and Canons, and on several different models, in several different modes, exposure compensation DOES NOT affect the reading on the screen. This can and has fooled many photographers into thinking their next shots on their next shoots were well exposed when in fact they were not. They forgot to take off the exposure compensation and could NOT see it in the viewfinder. It DID show exposure compensation in LCD panel on top of the camera but not in the viewfinder. Of course this was way worse with film than with digital where you would SEE if shots were too dark or too light.

My current Canon 30D ALSO works in this way in one of its E.C. modes.

So be careful you understand how your particular camera works with Exposure Compensation.