ISO or exposure compensation

[kabalman]

This may be a stupid question to ask, but will still ask. The aperture, shutter speed and ISO are considered the holy grail of exposure. How about the exposure compensation?

For example when I'm taking pictures inside the house, instead of increasing the ISO (and thereby introducing more noise), can I just increase the exposure compensation? Mine is an entry level DSLR and even that allows the exposure compensation to be increased to +5.0 (I presume 5 stops?).

What are the disadvantages of doing this? There must be some, otherwise this would be used more in my opinion. Our am I barking mad to even suggest something as stupid as this? Fine if I am, just want to know why.

 

[pablo_paul]

exposure compensation adjust the shutter speed either increasing or decreasing it. If the shutter speed falls lower than I want I would then increase the Iso last because it can introduce noise.

 

[Suvv]

If you are in Aperture Priority (A or Av)mode then dialling in Exposure Compensation will change the Shutter speed from whatever the camera has decided was "correct".
If you are in Shutter Priority (S or Tv) mode then dialling in Exposure Compensation will change the Aperture from whatever the camera has decided was "correct".
If you are in P (Program) mode then dialling in Exposure Compensation will change the Aperture and/or the Shutter speed from whatever the camera has decided was "correct".
In all cases you are not making the camera more sensitive or "better" you are just changing the exposure, the term Exposure Compensation does suggest that it is a way of compensating for low light or too bright light but it should be thought of as an Exposure Adjustment which can be applied when in one of the semi-auto modes.

 

[Phil V]

Kev put it well, but I'll try a different angle.
What your camera meter reads as a correct exposure isn't necessarily 'correct'.
Basically, the camera meter is looking for a mid grey tone** - so is expecting the light levels in your photo to average out at a mid grey. which would give you 'correct' exposure.
However if your subject is brighter than mid grey - a snow scene - or darker - a night shot, the camera will under / over expose. When using a semi auto mode, you would choose exposure compensation, when shooting manually, you'd set your meter reading for under / over exposure.

**Metering patterns:
In the old days all camera meters averaged the light across the whole scene, this is 'average metering'.
Later they concentrated the metering area towards the centre of the frame - 'centre weighted metering'
Modern cameras use an intelligent metering pattern which looks to compensate for dark points, highlights etc - 'evaluative metering' or 'matrix metering'
We also have a choice of partial or spot metering where the photographer can choose a small area of the scene to meter.

 

[kabalman]

Thanks for your replies. I have slowly graduated to shooting in the Manual mode, and away from the Aperture/Shutter Priority mode (as far as possible). Does this mean that setting the exposure compensation won't make a difference to the exposure in manual mode?

 

[CT]

I think it's important to understand why you have an exposure compensation facility on your camera in addition to being able to adjust aperture and shutter speed.

Exposure compensation never existed, nor was it needed until the the first aperture priority camera came on the market, which I think was the Pentax ME.

In aperture priority mode if you alter the aperture, the camera automatically adjusts the shutter speed to maintain the same exposure value and provide an exposure which the camera meter deems to be the correct one. Altering the ISO in an attempt to override the meter will simply result in the camera meter producing an identically exposed shot, as left to it's own devices the camera will always take what it considers the correctly exposed shot regardless of camera settings (*). In auto modes the meter is a silicon overlord which most of the time provides you with decent exposures in many situations, but it can get it wrong surprisingly easily and you need to be able to override it using your own judgement on these occasions.

Without an exposure compensation facility you would simply have no way of overriding the camera in auto modes and thats why it's there - to enable you to give more or less exposure than is indicated by the camera meter. You'll never see an exposure compensation dial on purely manual cameras because they simply don't need one.

(*) Altering the ISO to override the meter WILL work with a film camera as film will have a fixed ISO rating, which a digital sensor doesn't.

 

[Phil V]

Thanks for your replies. I have slowly graduated to shooting in the Manual mode, and away from the Aperture/Shutter Priority mode (as far as possible). Does this mean that setting the exposure compensation won't make a difference to the exposure in manual mode?

Yes.
Exposure compensation is to compensate for the camera's metering in auto modes.

This is a prime example of one of my soapbox issues.:bonk:

Shooting Manual isn't giving you anything that a semi auto mode would if you haven't got a solid understanding of exposure. Go back to my other post and read about metering modes (they're the really important bits). Then I'd recommend some more research on the internet, then some practice, creating the picture isn't about being able to say 'I shot it in Manual' which many believe. It's about understanding the light, metering that light properly then deciding whether your priority is to control the depth of field or shutter speed, (and now with digital your ISO to make the most of both).

Then the semi auto modes may help you shoot faster and more accurately, or they may not, but if you're choosing Manual, you'll at least be doing it because it suits you rather than as some 'badge of honour'.

And if the penny drops and you 'get' this, come back and say so, because internet forum's are full of people telling you that the only way to be in control is to shoot Manual, without the slightest acknowledgement of the important bit; Understanding your meter.
Thanks

 

[CT]

Phil is on the money actually - I shoot in aperture priority mode for probably 98% of my shots.

If you shoot in manual mode and simply balance the viewfinder curser in the centre of the scale, you might as well be shooting in an auto mode -you're simply balancing the exposure to what the meter deems to be correct and it can be wrong.

Shooting in manual mode isn't some some sort of promotion and it doesn't make you a better photographer. There are occasions when manual mode is an advantage but without an understanding of basic metering and how your camera meter works in it's various modes you'll forever remain confused. The mode you shoot in doesn't matter one jot as long as you understand how to override the camera meter when necessary and more importantly - why you need to.

Have a look in the Tutorials section - there are some good basic explanations of metering technique in there, including a particularly good one by Ed Bray.

 

[HoppyUK]

Good to start off the new year with a fundamental question and some good answers

The basic problem is that the important thing for correct exposure is the brightness of the light falling on the subject, eg the sun, but because that's either inconvenient to measure* (or even impossible) all on-board metering systems measure the light reflected from the subject, based on the assumption that when all the light and dark and medium tones are scrambled up, they will equate to mid-grey.

This works surprisingly well most of the time, but gets skewed when the subject is predominently light or dark, as Phil mentions above. The classic case is a bride and groom, when the light falling on them both is the same, and therefore the correct exposure for both is the same.

However, when you point the camera at just the bride, it sees only a lot of white and assumes that the subject is very bright and therefore needs less exposure, resulting in a grey dress (snow scenes give the same result). Metering just from the groom in black has the opposite result, the camera sees a dark subject and so increases the exposure making the groom too light.

The correct exposure for both lies somewhere between the two and smart systems like evaluative/matrix are able to detect scenes like this and will attempt to get it right, but they are far from infallible so you still need to apply your own judgement, and exposure compensation as necessary.

Or you can make your own settings in manual, ignoring the meter and using the LCD, the histogram and blinkies (highlight over-exposure alert, enabled in the menu) as your guide. This is an extremely accurate method of setting exposure, under any conditions, if you understand the basics and can read the historgram properly (easy - not as hard as it looks!).

* measuring the light falling on the subject is done by pointing the meter towards the camera, from the subject position. It's usually done with a hand meter and a white dome over the sensor, though you can do it in various other ways, including with a DSLR.

 

[CT]

Understanding exposure really isn't that difficult but you can write reams trying to explain what is a pretty basic principle. Generations of photographers have worked out that if you place the exposure to expose correctly for a mid tone grey which we call 18% grey- then all other tones in the shot including light and dark areas will be correctly exposed also. Unfortunately it doesn't always work when there are predominant light or dark areas in the shot (such as the bride's dress referred to by Hoppy above.) and on these occasions we need to switch off the auto pilot and take control ourselves.

Early cameras had full frame average metering (which Phil referred to earlier) These meters simply did what all meters do and looked to place the exposure around an 18%grey and they achieved this by mixing all the tones in the viewfinder down to a common colour rather like stirring a pot with a big stick . Whatever tone resulted the meter decided it was 18% grey regardless of what tone it actually was, so it was far from an ideal system.

Things have moved on since then and we have some very sophisticated metering systems in modern SLRs including Evaluative metering (Canon) and Matrix metering (Nikon). Both systems work in pretty much the same way and it's a fair bet that all modern SLRs regardless of manufacturer will have similar systems. The way these systems work is to divide the focusing screen into a number of invisible small segments and take individual readings from each segment which it then compares with each one to try to ascertain which is 18% grey and how the exposure should be adjusted to best expose the shot you see in your viewfinder. It's not just looking to place the exposure for 18% grey - it's taking the overall tones into account, where they fall in the scene and how important a particular tone is likely to be to getting the exposure right. It's a very sophisticated system.

If all of that wasn't impressive enough though, the camera then compares these readings with thousands of example shots stored in your camera in an attempt to get you the right exposure. It sounds fantastic and it is , but the fact is that good as it is it can be very easily fooled- it can't think but you can!

I'd urge everyone to try this simple test....

Set the camera to Evaluative or Matrix metering and take a shot of a piece of plain white paper filling the viewfinder. Now take a shot of a piece of black paper filling the viewfinder. What you'll get is two identical images both corresponding to 18% grey. If you look at the histogram you'll see a tall thin spike right in the centre representing 18% grey and no other tones.

What's happened is that in each case despite all that metering sophistication and all those separate little readings, all the tones are the same, so the meter simply assumes that white, black or any other tone at all is 18% grey regardless of whether it's actually white or black. The result is that the white image is under-exposed while the black one is over-exposed.

 

[s162216]

Exposure compensation never existed, nor was it needed until the the first aperture priority camera came on the market, which I think was the Pentax ME.

Close - It was the Pentax ES of 1972 (or technically speaking, the Pentax 'electro-spotmatic' of 1971 is the first but that was only virtually a prototype of the ES and was released in extremely small numbers in Japan, they were found to not be very reliable and each one is slightly different in some way) and that introduced the concept of exposure compensation with a small dial that let you set +1,+2 or -1 stops of compensation although you could also put it in any position between the two clicks to get whatever you liked.

 

[HoppyUK]

While we're on a roll then

Even when exposure is correct, that doesn't always mean everything will be successfully exposed, because of the limitations of the sensor's dynamic range. Some things will be too bright and will blow to pure white (and if you have blinkies enabled, which you should, they will be flashing like mad) and the darkest tones may hardly register at all.

A common example is a landscape where if you expose correctly for the foreground, a bright sky will just bleach to white - it's more than the sensor can handle. Evaluative/matrix will attempt to adjust the exposure for this, because it knows there's a very light area at the top and how bright it is, it knows the camera is in a horizontal framing position, and it knows the lens is focused on a distant setting. So there's a good chance that this is a landscape shot (though it might not be!) and it will therefore reduce the exposure in an attempt to hold on to some sky detail, but there's only so much it can do.

This is why graduated filters (darker at the top, fading to clear) are popular for landscape as they darken the sky and reduce the dynamic range so the sensor can handle it. There are other ways of adjusting dynamic range, like using flash to brighten the foreground, or HDR technique which blends several different exposures to compress all the tones into a manageable dynamic range, but that's another story.

Giong back to manual for a moment, it's a bit of a misnomer IMHO. Calling it Set & Lock is a more accurate description, because that's all it does, whether the exposure is right or wrong.

 

[CT]

I do remember the ES.I bought an ME as soon as it hit the market and took to it like a duck to water. I still remember the controversy around the auto concept at the time and how 'proper' photography was doomed!

 

[Goody13]

Yes.
Exposure compensation is to compensate for the camera's metering in auto modes.

This is a prime example of one of my soapbox issues.:bonk:

Shooting Manual isn't giving you anything that a semi auto mode would if you haven't got a solid understanding of exposure. Go back to my other post and read about metering modes (they're the really important bits). Then I'd recommend some more research on the internet, then some practice, creating the picture isn't about being able to say 'I shot it in Manual' which many believe. It's about understanding the light, metering that light properly then deciding whether your priority is to control the depth of field or shutter speed, (and now with digital your ISO to make the most of both).

Then the semi auto modes may help you shoot faster and more accurately, or they may not, but if you're choosing Manual, you'll at least be doing it because it suits you rather than as some 'badge of honour'.

And if the penny drops and you 'get' this, come back and say so, because internet forum's are full of people telling you that the only way to be in control is to shoot Manual, without the slightest acknowledgement of the important bit; Understanding your meter.
Thanks

Thank God for that! I am by no stretch of the imagination an expert photographer, although I had my first SLR in 1982, so I would like to think I have gained an understanding of exposure in that time. I, however, am quite happy to use Av, Tv or P and dial in compensation as I see fit, so it can get annoying when people suggest that shooting manual is the right way to do and infer that you are only any good if you do shoot in manual.

I use manual very occasionally in extreme lighting conditions, but other than that, I find the auto modes suit me well.

 

[kabalman]

I'm glad my comment about shooting in manual mode has resulted in some angry comments, but I would like to clarify that when I said "graduated to shouting in manual mode" I meant I have learned to shoot in manual mode. I have by no means stopped shooting in the auto modes.

Thanks for all the useful comments though.

 

[Suvv]

My take on Manual v. the Semi-Auto modes is:

If you are in a Semi-Auto mode and the light changes the exposure will also change , however if the scene or subject changes then the exposure will still change even though the light levels may be the same .
If you are in Manual and the light changes the exposure will not change , however if the scene or subject changes the exposure will not change

A couple of examples:

Imagine a landscape, in this case the scene itself will not change much but the lighting may, therefore you need to change the exposure - a Semi-Auto mode will do that itself but Manual will not unless you keep changing settings .

Imagine shooting a bird which flies across different backgrounds, trees, sky, ground etc. under the same light, you need the same exposure for the bird but the different backgrounds will cause the camera to suggest different exposure - a Semi-Auto mode will keep changing the exposure but Manual will keep it constant .

As has been said already, understand all the different modes and what Exposure Compensation does and when to use it and then select the mode which suits your needs at the time.

 

[scottthehat]

Imagine shooting a bird which flies across different backgrounds, trees, sky, ground etc. under the same light, you need the same exposure for the bird but the different backgrounds will cause the camera to suggest different exposure - a Semi-Auto mode will keep changing the exposure but Manual will keep it constant .

true but if you have exposure locked via ae-l button of on half shutter press then it wont.

 

[Phil V]

I'm glad my comment about shooting in manual mode has resulted in some angry comments, but I would like to clarify that when I said "graduated to shouting in manual mode" I meant I have learned to shoot in manual mode. I have by no means stopped shooting in the auto modes.

Thanks for all the useful comments though.

It's not anger, it's frustration, and clearly it's necessary:bonk:.

In your words; you've 'learned to shoot in manual mode', which is how many people see it -the really big issue is, and I apologise for my bluntness;

You haven't learned to 'shoot' in Manual mode at all, all that you have done is worked out how to switch the camera to M and then centre your meter. Your original question is proof of this. You'll have 'learned' to shoot in Manual when you've looked at a potential photograph, worked out how the situation will effect your metering, what your priorities are (speed of operation, accurate exposure, prioritising shutter speed or depth of field), and then decided to shoot in Manual for your chosen result.

I really do blame the internet forum, 'shoot manual -it's the only way' for pushing this. As I said, concentrate on learning about exposure and metering, whether you're shooting Manual or Program doesn't make any difference - as long as you understand program shifting and exposure compensation. The metering is the important element and it gets lost in the internet's ridiculous statements about auto exposure modes.

As you can see, I feel strongly about this, but only because it's a right load of nonsense that gets in the way of people learning the stuff that will really help them.

I've actually seen people argue that 2 shots with exactly the same SS/ ISO /aperture will be different shot in M to AV or TV, that's how mental this can become.

 

[Dippy]

a reasobale question to ask in the first place with some brilliants answers, a very useful post to read! Thanks to all who input x

 

[HoppyUK]

Good luck in your quest Phil, though I fear you may wear your fingers to the bone in the attempt.

Folks believe what they want to believe, and using manual is one of those things that makes them feel they're in control and doing a better job. I faced hoots of derision when I announced on a motoring forum that I wanted an automatic car, and despite the fact that it changes gear faster and more smoothly than Jenson Button, it clearly put my manhood in question.

Shooting Raw is another must, alongside spot metering and second-curtain sync. The good thing is that most of the time is really doesn't matter, but it does get a bit depressing.

I'm surprised that nobody on this thread (and it's been a good thread) has so far mentioned that dreadful book Understanding Exposure by Bryan Peterson. It's very popular because people that don't understand exposure (even after reading it) keep saying it's good and so the myth is perpetuated!

 

[Phil V]

Good luck in your quest Phil, though I fear you may wear your fingers to the bone in the attempt.

Folks believe what they want to believe, and using manual is one of those things that makes them feel they're in control and doing a better job. I faced hoots of derision when I announced on a motoring forum that I wanted an automatic car, and despite the fact that it changes gear faster and more smoothly than Jenson Button, it clearly put my manhood in question.

Shooting Raw is another must, alongside spot metering and second-curtain sync. The good thing is that most of the time is really doesn't matter, but it does get a bit depressing.

I'm surprised that nobody on this thread (and it's been a good thread) has so far mentioned that dreadful book Understanding Exposure by Bryan Peterson. It's very popular because people that don't understand exposure (even after reading it) keep saying it's good and so the myth is perpetuated!

I know, it drives me bats, and I'm too much of a pragmatist to make the best of it. Because whilst people are hanging on to all this drivel they don't understand why their photography isn't improving and still have to pay people to take photo's.

Don't tell me that book's rubbish:bonk:
I've bought it for people to 'help' them when I couldn't get them to listen to me.

 

[HoppyUK]

I know, it drives me bats, and I'm too much of a pragmatist to make the best of it. Because whilst people are hanging on to all this drivel they don't understand why their photography isn't improving and still have to pay people to take photo's.

Don't tell me that book's rubbish:bonk:
I've bought it for people to 'help' them when I couldn't get them to listen to me.

Haha! In which case, while they'll know all about The Sky Brothers and Mr Green Jeans with techniques for shooting film, they will know nothing about the histogram, or ETTR, or blinkies, or adjusting white balance, JPEG and Raw... The best and most useful tools for optimum digital exposure, zero - and that includes last year's new, updated edition :shrug:

 

[Dblock]

It's not anger, it's frustration, and clearly it's necessary:bonk:.

In your words; you've 'learned to shoot in manual mode', which is how many people see it -the really big issue is, and I apologise for my bluntness;

You haven't learned to 'shoot' in Manual mode at all, all that you have done is worked out how to switch the camera to M and then centre your meter. Your original question is proof of this. You'll have 'learned' to shoot in Manual when you've looked at a potential photograph, worked out how the situation will effect your metering, what your priorities are (speed of operation, accurate exposure, prioritising shutter speed or depth of field), and then decided to shoot in Manual for your chosen result.

I really do blame the internet forum, 'shoot manual -it's the only way' for pushing this. As I said, concentrate on learning about exposure and metering, whether you're shooting Manual or Program doesn't make any difference - as long as you understand program shifting and exposure compensation. The metering is the important element and it gets lost in the internet's ridiculous statements about auto exposure modes.

As you can see, I feel strongly about this, but only because it's a right load of nonsense that gets in the way of people learning the stuff that will really help them.

I've actually seen people argue that 2 shots with exactly the same SS/ ISO /aperture will be different shot in M to AV or TV, that's how mental this can become.

Very true, Its like if you dont shoot manual you dont like photography or something

Its true, I use manual mode when the camera wont give me what I want or doesnt know what I want. But other times Av or Tv and sometimes P is fine too. I generally take pictures of people and the Av is great you can get pretty much what you want with the camera taking the bulk of the calculating. In that time your messing about with settings you could have missed a great shot.

Im no pro but I am using Av and Tv more and more. But some of my best shots are in P because someone pulled a face at that time or something happened. Just my opionion though.

 

[HoppyUK]

Very true, Its like if you dont shoot manual you dont like photography or something

Its true, I use manual mode when the camera wont give me what I want or doesnt know what I want. But other times Av or Tv and sometimes P is fine too. I generally take pictures of people and the Av is great you can get pretty much what you want with the camera taking the bulk of the calculating. In that time your messing about with settings you could have missed a great shot.

Im no pro but I am using Av and Tv more and more. But some of my best shots are in P because someone pulled a face at that time or something happened. Just my opionion though.

LOL yes Use whatever gets the job done best.

I think most folks use a combination of aperture-priority and manual usually. A few on-line polls have come up with that, and that's what I use too. I'm in the studio a lot so that's manual, but out and about almost aways Av. Hardly ever use that now.

That has changed over the years, when I used shutter-priority a lot because camera shake was a major problem with low ISO film and no IS meant you just had to always keep the shutter speed up. Hardly ever use that now.