Understanding Exposure Compensation

jamesward93

jamesward93

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Can anyone offer some advice on exposure compensation? I roughly know what it is and have a played around with it a bit while using the camera, but cant really get my head around it.

Any advice welcome
 
Is it the theory or the howto that your having trouble with?
 
A bit of both really, i know how to set it on the camera, thats not the issue, but its more when and the benefits of it. So the theory i more than anything
 
when i know the camera has it wrong.. say shooting towards the sun.. the camera will under expose the subject (you know.. dark face but rest of scene perfect) so I have to over expose and the face becomes perfect exposure.. so I compensate for the scene..



now I have written it i am thinking someone else can probably explain it better.. i ahve it in my head :)
 
spot read the area you are interested in
when you recompose and see the readings vary...use the +/- adjustment to set the exposure
this is compensation based on actual readings

i do spot reading on the subject...and focus
and then recompose...both go together

review...alter...reshoot
delete unwanted
 
So If I increase exposure compensation (+) for a shadow (or something) I run the risk of over-exposing other parts of the frame?
 
Correct. You have to shoot within the capabilities of the camera - some scenes just have too much contrast for the sensor to handle - and you have to decide (not the camera) where the correct exposure should be.

Camera exposure meters are pretty good most of the time. They are reading reflected light from the subject - not the most accurate way - but they compensate and are very reliable 90% of the time. If you want more accuracy use an incident meter (light falling on the subject) or take spot readings from key areas.

Whatever you do the camera has a brightness range and you have to work within that.
 
soliberus said:
So If I increase exposure compensation (+) for a shadow (or something) I run the risk of over-exposing other parts of the frame?
Click to expand...

yes because you cant under/over expose parts of a picture.. in my example shooting into the sun. i need to over expose to get a face right but then all the background is over exposed.
 
That explains the problem I had on Saturday - I went on a "photo walk" and the sun was quite bright. The problem I came across was this: I wanted to take a photo of a building, but the one wall is in the shadow and the other in direct sunlight. I exposed for the wall in the shadow and as a result the wall in the sun was grossly over-exposed. Exposed for the wall in the sun and then the wall in the shadow was way too dark.

Is this a case of give up and move on to the next photo opportunity?
 
note the settings for each wall.. set your camera for inbetween... go home, load up photoshop and bobs yer auntie :)
 
KIPAX said:
note the settings for each wall.. set your camera for inbetween... go home, load up photoshop and bobs yer auntie :)
Click to expand...

Not quite that simple - but if you shoot in RAW you may have a chance of saving things. Sounds like the contrast was just too great - and probably wouldn't make a great pic anyway. With buildings you some times have to visit a few times to get the sun just right. Don't give up on the pic - just go back at a better time of day!
 
ha :) I know but I couldnt do a whole tutorial on it.. the concept is to go inbetween and then see what you can get post process :)
 
Could you not capture 2 images in RAW, 1 with the correct exposure for the lighter wall and one for the darker wall, then merge the 2 RAW files in photoshop?

Or am i cheating?
 
getting into the realms of HDR - camera needs to be on a firm tripod - sometimes it might work - sometimes better to go back when the light is better - it's all about getting the best light - whatever you're shooting.
 
jamesward93 said:
Could you not capture 2 images in RAW, 1 with the correct exposure for the lighter wall and one for the darker wall, then merge the 2 RAW files in photoshop?

Or am i cheating?
Click to expand...

That tends to be difficult :( with hand held or moving subjects... but I do just that with tufusepro when using a tripod.

the reason we use exposure compensation is to compensate for the limitations of exposure meter measurements.

There is no such thing as a scientifically correct exposure. Just one that captures the brightness range you intend. in most situations the brightness range of the subject is greater than you can capture, so you must make a choice. Exposure compensation changes the range captured but not the range the sensor can capture. it is always a compromise. :'(
 
The camera reckons that the scene is an average Grey (18% grey was the standard but with digital 12% grey is often used)
If the scene is lighter than the average Grey, as snow would be, the camera thinks that it is an average scene on a bright day so it reduces the exposure to make the snow average Grey. You need to overexpose to compensate.
If you are photographing something black, an animal for example, the camera thinks that it is an average scene on a dull day so it increases the exposure to make the black animal average Grey. You need to underexpose to compensate.

More problems can arise because of the "intelligent" cameras we now have, some of them actually compare the meter output with readings in their memory and adjust the final reading accordingly.

In the old film days I used a seperate meter to take incident light readings where you metered the light source and not the subject, it did not matter if the subject was white, black or anything in between. The light from the source is what matters. Because we now meter the reflected light we have to compensate for whatever is doing the reflecting.
Worth repeating - The light from the source is what matters, if you think about that and understand it you will realise why compensation is needed.


Do this at home :)
Put the camera on Auto and take a picture of just a white card (fill the viewfinder with the card), then in the same lighting take a picture of just a black card, in post processing convert both to B&W (to get rid of any colour casts) and see what you get.
 
:agree:

I wish you had posted before me, great explanation and would have saved my typing fingers. :)
 
KIPAX said:
yes because you cant under/over expose parts of a picture.. in my example shooting into the sun. i need to over expose to get a face right but then all the background is over exposed.
Click to expand...

its wise to set up with most of your data within +/- 2 stops latitude

for trannies it was very tight...get the sun behind something...

you can take a reading direct from your hand or the face in question
stabbing at compensation readings is like one had two left feet
walk man walk!!! the trip is worth it...

i am processing some isles of scilly holiday snaps and i do see a vast exposure range...glad i took 3 of every one...that is my crutch
 
The building problem - you coul dhave done something about it at the time. It would simply involve using a neutral density grad, set to reduce the brighter wall, not to exactly the same as the shadow, but to drop the difference in EV between the two (I have just realised I have introduced a new term EV - I'll say it another way!)

The ND grad would reduce the amount of light hitting the bright wall. You choose one (yes, you have a few) that drops the amount of light getting through to the lens from that wall, in effect locally changing the exposure, it DOES NOT change the amount of light hitting the wall - just the light bouncing off it that is allowed through the lens. This gives the sensor a chance to resolve the scene. You have to meter the scene WITHOUT the filter, note the settings, then you cheat the camera by setting what it says you need without the filter in place (it doesn't know you are about to fit it. Even when you have fitted it, it doesn't know what you are doing!) The camera then records the scene YOU HAVE CREATED FOR IT.

Remember, a camera meter has no idea what it is looking at, nor does it know what youwant to do. It is trained to pick the happy middle ground, by producing a good average picture. We don't want good average, we want superb better than average. So do you your own thing and CONTROL the camera. You tell it what to do, not the other way round. That is the crux of photography - maintain control, even if you are wrong.
 
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