Exposure Compensation Question

[Abitconfused]

I understand using EC to adjust for greater or lesser indices of reflection but is EC also the best way to adjust the histogram toward white point or black point should a gap be incicated what an image is reviewed in camera?

[Tronhard]

In the end there are only 3 variable for exposure: ISO, shutter speed and Aperture. When you use one of the auto or semi auto modes you are giving control over one or two of the other variables - for example if you go to aperture priority you are allowing the camera to calculate the correct exposure (according to its algorithms) and adjust shutter speed and (if you allow it) ISO. The same thing would happen in shutter priority or program mode.

Exposure compensation works on the camera's algorithms within those parameters to allow you to select the value of your choice and then manipulate the resulting solution for the other variable(s) using exposure compensation. Thus if you don't like the solution for an aperture you set you can force under or over exposure with the EC dial. This does not apply to manual mode as you have full control over the variables.

[William W]

I believe that I know exactly what you mean, but, previously, I have needed to clarify what is exactly meant by "Manual Mode" when the phrase is used in this context . . .

I believe Trev specifically means in this context "Manual Mode" (i.e. setting the dial to "M") ... AND ... having "Auto ISO" DIS-engaged

. . . Thus if you don't like the solution for an aperture you set you can force under or over exposure with the EC dial. This does not apply to manual mode as you have full control over the variables.

I think (Nikon experts please), that Nikon (perhaps others too) will allow Exposure Compensation when the camera is in "Manual Mode" and when Auto ISO is selected.

This is a feature which Canon DSLRs lack and I understand Trev (like me) is/was a Canon user . . .

This Nikon EC feature can be very useful and is perhaps applicable to the Nikon Df.

WW

[Manfred M]

Bill - on Nikon, when in manual (M) mode and auto-ISO is on, then changing the exposure compensation changes the ISO.

[Manfred M]

I understand using EC to adjust for greater or lesser indices of reflection but is EC also the best way to adjust the histogram toward white point or black point should a gap be incicated what an image is reviewed in camera?

Ed - from a purely technical standpoint it is important that the data that the camera captures does not crush shadow detail or clip highlight detail, so exposure compensation (EC) is useful when the histogram shows that this has happened. Using EC in this way ensures that we have "good" data to work with in post processing.

There are a couple of caveats that go with that statement:

1. The histogram on that our cameras display are based on a JPEG image, so if we are shooting in raw, there is usually around one stop of "headroom", i.e. the histogram indicates clipping, but there is really some usable data in the raw file.

2. If the scene we are shooting exceeds the camera's dynamic range at a given ISO setting, then there could be clipping at both ends and there may be nothing one can do about it.

[Tronhard]

What I tried to say (badly!) was that on some cameras you can fix the ISO, either within a defined range or to a specific value. If the ISO is not so limited then EC will likely use that as one of its variables.

To go with Bill's comments. I found that SOME Canon cameras allow the ISO to be fixed or limited while others do not, and certainly my particular Nikon has the ability to "lock" the ISO. If the ISO is so limited, then EC will work on the other variable: if you are in Aperture Priority it will play with the Shutter speed and vise versa. If are in program mode (where the camera will allow you to vary either the shutter or aperture and will change the other accordingly, EC will alter that algorithm.

If you have access to Lynda.com there are some excellent videos on this subject by Ben Long

I tend to use Aperture Priority mostly, and I use EC when I am not satisfied with the camera's solution to the image that I am metering, so the EC allows me to modify that solution on the fly without taking my eye of the viewfinder.

I believe that I know exactly what you mean, but, previously, I have needed to clarify what is exactly meant by "Manual Mode" when the phrase is used in this context . . .

I believe Trev specifically means in this context "Manual Mode" (i.e. setting the dial to "M") ... AND ... having "Auto ISO" DIS-engaged



I think (Nikon experts please), that Nikon (perhaps others too) will allow Exposure Compensation when the camera is in "Manual Mode" and when Auto ISO is selected.

This is a feature which Canon DSLRs lack and I understand Trev (like me) is/was a Canon user . . .

This Nikon EC feature can be very useful and is perhaps applicable to the Nikon Df.

WW

[pnodrog]

With Nikon EC simply offsets the metered result and the centre point is displayed in the offset position in A, S or M exposure modes. In all other respects the exposure modes behave as usual but use the offset exposure value.

I would have to check in the manual as to how it affects any other mode as I never use them.

For situations such as taking photographs with a snow background and wanting to apply a positive EC it still being active in M mode with auto ISO is a distinct advantage. In M mode without auto ISO you need to remember you are referencing the apature and speed values to an offset exposure indication.

[Abitconfused]

Will increasing ISO also increase dynamic range (a little??) or are we totally stuck with the dynamic range of the sensor? Not that I feel dynamic range is always important. I see no need to make a camera see like a human or an owl (high dynamic range) but sometimes more detail inshadow is useful even as a starting point for Raw.

[Manfred M]

Will increasing ISO also increase dynamic range (a little??) or are we totally stuck with the dynamic range of the sensor? Not that I feel dynamic range is always important. I see no need to make a camera see like a human or an owl (high dynamic range) but sometimes more detail inshadow is useful even as a starting point for Raw.

No, it actually has the opposite effect. As ISO increases, dynamic range decreases. The "base" ISO, i.e. the lowest numeric ISO setting on your camera has the best dynamic range, lowest amount of digital noise and the best colour depth.

The reason is fairly simple. In a digital camera, your sensor has a fixed ISO and everything we think of as ISO is created by amplifying the signal, which is why image quality decreases.

[pnodrog]

Will increasing ISO also increase dynamic range (a little??) or are we totally stuck with the dynamic range of the sensor? Not that I feel dynamic range is always important. I see no need to make a camera see like a human or an owl (high dynamic range) but sometimes more detail inshadow is useful even as a starting point for Raw.

The dynamic range is a function of the sensor and the ISO settings. EC can help by adjusting the exposure to take maximum advantage of the dynamic range available.e.g. best exposure or ETTR etc

[Abitconfused]

I see the truth of it. Exposure compensation, then, is a useful tool when adjusting for brightness other than 50% or when pushing toward white point or black point for sake of better tonal values. It that it?

[pnodrog]

I see the truth of it. Exposure compensation, then, is a useful tool when adjusting for brightness other than 50% or when pushing toward white point or black point for sake of better tonal values. It that it?

Basically yes...🙂

[Tronhard]

The dynamic range of the sensor and processor are a defining limit. Changing the settings for exposure will work within those limits and, for example noise. That said technique can make a big difference as can the type of file you create. Shooting in RAW will give you a lot of variables to play with, shooting in JPG is different because algorithms in the camera have processed and compressed the image to achieve the file size and type.

Do you have access via your library to Lynda.com? Check and see, because lots of them do...
If so look at Ben Long's video course on File Formats - apart from being informative, its highly entertaining.

Will increasing ISO also increase dynamic range (a little??) or are we totally stuck with the dynamic range of the sensor? Not that I feel dynamic range is always important. I see no need to make a camera see like a human or an owl (high dynamic range) but sometimes more detail inshadow is useful even as a starting point for Raw.

[Manfred M]

I see the truth of it. Exposure compensation, then, is a useful tool when adjusting for brightness other than 50% or when pushing toward white point or black point for sake of better tonal values. It that it?

I'd suggest something even simpler. It is a way for the photographer to correct for the assumptions built into the camera's metering system when the shooting conditions fool the meter into selecting an inappropriate exposure. Shooting at night, into the sky or on a snowy day are typical examples of where this happens.

[Tronhard]

I'd suggest something even simpler. It is a way for the photographer to correct for the assumptions built into the camera's metering system when the shooting conditions fool the meter into selecting an inappropriate exposure. Shooting at night, into the sky or on a snowy day are typical examples of where this happens.

Eliquently put Manfred... That was what I was trying to explain...

[Abitconfused]

Thank you all....

[Dave Humphries]

Touched on above, in various places, by various esteemed members, was the difference in behaviour of EC between Canon and Nikon in "Manual" Mode.

IIRC (and I'm pretty sure I do) with Nikon, even in Manual mode with Auto-ISO DISengaged, changing EC will bias the meter, which in turn will (for a given scene) 'encourage' you to turn whatever knobs are necessary to effect the exposure change you want.

e.g. If you're shooting a person wearing dark clothes in a snowy scene, we probably know the camera would, left to its own devices (auto), underexpose the scene, so we set some +EC to compensate.

In full Manual mode (with Auto-ISO disengaged) and not using spot metering, the same would happen if we expose with the meter centred.

With most/all Nikon cameras*, we can still use EC to change how the meter displays 'correct' exposure, so if the scene doesn't change**, but the lighting does (say the sun comes out), the meter can again be centred for a correct exposure and this will still include the offset you desire, in order to have white (not grey) snow (and an even darker subject).

Under the same circumstances, I believe* Canon cameras would not see a change of metering when the EC control is altered.

* Last time I researched this was a few years back, but I'm not aware of it having changed.
** e.g. the area ratio of white snow to darker subject remains the same, since this is what causes the exposure error when we use average or centre-weighted meter modes willy-nilly.

Of course, if you're used to using spot metering, that will probably remove the need for this 'Nikon benefit', since you'll very likely be metering on a single tonal value anyway - and you'll have picked a tone that is mid-grey and result in the correct exposure.

[DanK]

Manfred (post 14) beat me to it. I'm going to suggest that you step back further and separate two things: getting the exposure you want, and deciding how to get it.

The answer to the first question has two parts. First, you don't want to clip at either end of the histogram. Second, in most cases, if the histogram is less wide than the full range, you are better off exposing to the right and having the mass of the histogram nearer the top end.

The answer to the second question is: there are lots of ways to get to the exposure you want. You have only three variables, as noted in an earlier post: shutter speed, aperture, and ISO. In general, to keep dynamic range at its maximum and noise at its minimum, you are better off with the lowest ISO you can manage. The other two you chose based on other factors, such as how much depth of field you want and whether you have to freeze motion.

Once you have figured out the values of those three that you want, it makes no difference how you choose to get there. For example, let's say that the optimal settings for a given photo are 1/125, f/8, ISO 100. However, because of the nature of the scene, the particular metering you chose leads the camera to select 1/500, f/8, ISO 100, shifting the histogram two stops to the left of where you want it. This can happen, for example, if you meter off the entire scene and the scene includes a lot of snow. You can use EC to adjust upwards, you can meter differently, or you put the camera in manual mode and select 1/125 yourself. It makes no difference which of these methods you use.

[Tronhard]

A good demonstration of interrelationship between ISO, shutter and aperture is to put your camera in Program Mode. Point at a constantly lit target and take a meter reading. Then take turns rotating the aperture, then the shutter, and then the ISO. As you do so the camera will compensate with the other variables (according to the algorithms of the manufacturer) to come up with the same exposure result - if you are comfortable with the relationship between those variables' values.



In Program, Av or Tv modes you can override the algorithms by using the EC dial as follows:


In FULL manual mode - i.e. where you set all three variables yourself, EC is not effective, You will see the exposure results of your settings in the viewfinder exposure vernier and you will adjust accordingly - there is no algorithm to override.

Manfred (post 14)

The answer to the second question is: there are lots of ways to get to the exposure you want. You have only three variables, as noted in an earlier post: shutter speed, aperture, and ISO. In general, to keep dynamic range at its maximum and noise at its minimum, you are better off with the lowest ISO you can manage. The other two you chose based on other factors, such as how much depth of field you want and whether you have to freeze motion.

Once you have figured out the values of those three that you want, it makes no difference how you choose to get there. For example, let's say that the optimal settings for a given photo are 1/125, f/8, ISO 100. However, because of the nature of the scene, the particular metering you chose leads the camera to select 1/500, f/8, ISO 100, shifting the histogram two stops to the left of where you want it. This can happen, for example, if you meter off the entire scene and the scene includes a lot of snow. You can use EC to adjust upwards, you can meter differently, or you put the camera in manual mode and select 1/125 yourself. It makes no difference which of these methods you use.

[Tronhard]

I have a Nikon Df, which granted is a fairly unique box as it is meant to emulate a film camera in its behaviour.
If I set the ISO to locked then it remains so. It makes sense for a couple of reasons:
1. Film cameras had the ISO locked for the whole film (unless you went for push processing, but that's a whole different story).
2. In manual one wants to control the exposure, usually by adjusting aperture and shutter, having the ISO keep changing on its own would be defeating the purpose.

Touched on above, in various places, by various esteemed members, was the difference in behaviour of EC between Canon and Nikon in "Manual" Mode.

IIRC (and I'm pretty sure I do) with Nikon, even in Manual mode with Auto-ISO DISengaged, changing EC will bias the meter, which in turn will (for a given scene) 'encourage' you to turn whatever knobs are necessary to effect the exposure change you want.