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.

[tegan]

Interesting! In Minolta, Sony Alpha, and Leica the f stop changed in the viewfinder when I adjusted exposure compensation. I did not have a Nikon or Canon around at the time.

Tegan

[Marko]

It really does depend on the camera.

For me this is a clear flaw in the software that runs the camera. You should ALWAYS see the true exposure in the camera's viewfinder OR at least see a plus /minus sign with the letters EC and the degree of EC (+1/3, -2 etc.)

[Beginner]

I am confused about Exposure Compensation being "minus" or "positive"... I have read on one or two websites and in the manual for this camera that to tone down too-bright or too- white areas, one should make the Exposure Compensation more positive. This makes it worse!

So, I am using negative numbers to cope with some bright backlighting or brightly-lit distant areas in a scene... plus keeping the ISO low.

There seems to be some opposite advice on this subject. Can others help?

[Travis]

I am confused about Exposure Compensation being "minus" or "positive"... I have read on one or two websites and in the manual for this camera that to tone down too-bright or too- white areas, one should make the Exposure Compensation more positive. This makes it worse!

So, I am using negative numbers to cope with some bright backlighting or brightly-lit distant areas in a scene... plus keeping the ISO low.

There seems to be some opposite advice on this subject. Can others help?

They advice you are reading is backwards...

If your camera is reading the scene too bright you must pull back the exposure compensation.... ie -0.3

If your camera is reading the scene to dark you must increase the exposure compensation ... ie +0.3

Using the example of Aperture Priority mode (or av Canon) exposure compensation merely adjusts the shutter speed to compensate the exposure

example

Assuming you are locked in an aperture of 2.8 the camera might suggest the use of a 1/125 to properly expose your scene. If the image produced was overexposed by 1 stop(too bright), you would set your exposure compensation -1.0. The resulting adjustment by the camera would double the shutter speed 1/250 to properly expose the shot.

In manual mode you will not typically use exp comp. You will simply use the cameras meter to make your adjustments.

[tegan]

I am confused about Exposure Compensation being "minus" or "positive"... I have read on one or two websites and in the manual for this camera that to tone down too-bright or too- white areas, one should make the Exposure Compensation more positive. This makes it worse!

So, I am using negative numbers to cope with some bright backlighting or brightly-lit distant areas in a scene... plus keeping the ISO low.

There seems to be some opposite advice on this subject. Can others help?

Minus underexposes and makes it darker. Plus makes it brighter in exposure compensation. A LOW ISO however tends to increase contrast, so an ISO of about 400 would be better.

For a bright backlit scenic a polarizing or graduated ND filter is needed to control the brightness from the sky and yet still expose the foreground correctly.

If people are in the foreground then you need to use fill flash or for those that have it in their camera menus: a dynamic range control.

Tegan

[baddness]

Travis, how does one use the metering in their camera? I've been shooting in manual. I'm still trying to figure out the metering. In the manual it says to leave it to default and that the professionals worry about the metering lol

[tirediron]

Travis, how does one use the metering in their camera? I've been shooting in manual. I'm still trying to figure out the metering. In the manual it says to leave it to default and that the professionals worry about the metering lol

If all you want to take is snapshots, sure, that'll work, otherwise, it's crap advice. This is actually a hugely complicated topic; your best bet would be to head to either your local library or a used book store, and find a good 'How to' book on photography from the late 70s or earlier. Exposure techniques are exactly the same now as they were then, with the exception of rather than exposing for the shadows and developing for the highlights, we now expose for the highlights and process for the shadows.

The reason I'm suggesting an older book like that is because in the days when the use of hand-held light meters was common, a lot more emphasis was put on how to meter scenes correctly (ie The Zone System), even a lot of good books today (With the possible exception of Bryan Peterson's "Understanding Exposure") pay little more than lip service to the correct methods of properly metering a scene.

[Travis]

Travis, how does one use the metering in their camera? I've been shooting in manual. I'm still trying to figure out the metering. In the manual it says to leave it to default and that the professionals worry about the metering lol

wow!.... you might want to pour some gas on that manual and burn it.... feel free to add your own sinister laugh as it's reduced to ashes...

not sure what you are shooting with but generally in manual mode you can see the cameras meter through the viewfinder.... most have tiny little bars that stray to the left of right of center.... the meter shows you if the image will be overexposed or underexposed based on your aperture/shutter selections... you want the meter to be in the center for a correct exposure...

if you meter shows to the left or right you will have to select either a different shutter speed or aperture until the meter reads in the center..


Use the virtual camera on site listed below..... in fact absorb most of that site.... it will really help get you started....

http://www.camerasinteractive.com/home.php