Exposure compensation

The other day I was shooting some horses that were being putthrough their paces jumping at a stable outside of town. The light was fairlypoor and so we were trying to get as much lens opening ast we could. I wasshooting a Nikon D3S in manual mode. Iwas shooting 160 sec at f/2.8, ISO 2500. The exposure compensation was set at0. For whatever reason I changed the exposure compensation to +2/3, but nothingelse was changed. The two images were almost identical in content but thesecond one was obviously lighter than the first one, which is what you wouldexpect. My question is this, it is my understanding that total exposure isdetermined by speed, amount of light, and ISO. None of these changed asrecorded in the meta data. What is change to get the lighter image when changingthe exposure compensation? By the way the lens was a f/2.8 and I was shootingwide open. I hope my question is clear,if not please tell me what is not clear and I will try to correct it.

Thanks for any help you can give me.
Mac

Maybe I am totally off the mark, but it was my understanding that exposure comp means nothing in manual mode. It is a way of telling the camera to change settings up or down from the automatically selected value in one of the auto modes.

Ian,
it is my understanding that what you say is true nof Cannon, but not of Nikon.

Mac

What change was the light when in manual mode your camera does not change one of the settings when the light changes. For example lets say your shooting a middle tone scene on a cloudy day and after setting your shutter and aperture you get a meter reading of 0 which gives you a perfect exposure for your scene a few minutes latter the sun breaks thru for a few minutes and now the scene is metering at +2 if you take an image now without making an adjustment to to either the shutter speed or aperture your image will be overexposed. Now let take the same scenario and instead of shooting in manual your shooting in aperture mode when the suns starts to shine the camera will automatically change the shutter speed to keep the scene metered at 0. In manual you need to pay attention to the light and make adjustments as it changes in one of the auto modes you need to pay attention to the subject and BG and make adjustments as they change in tonalities.

If you are truly in Manual mode (i.e. no auto-iso) and not using flash, then the exposure compensation setting should have
no effect on the resulting image. In other words, if you have two images with the same shutter, aperture, and ISO in the metadata,
then they should look like identical exposures regardless of how the EC is set. However, setting EC WILL affect the metering readout
in Manual mode. For example, let's say you determine your manual exposure settings by spot metering a gray card and zeroing the meter.
That will work fine as long as the EC is set to 0. If you change the EC, it will bias the meter readout by that amount. In effect, the EC in
manual mode changes the meaning of 0 with respect to the metering readout. For example, if you set the EC to +1 and then spot meter
a gray card and zero the meter, the settings you end up with will be one stop brighter than they would be if EC was set to 0. To get the
correct exposure with EC set to +1, you would spot meter the gray card and change the settings until your meter readout is at -1.
This is true for Nikon but not Canon. In fact, with Canon, there is no way to even enter an explicit EC in Manual mode.

But if you are using Nikon flash (prior to the D4), setting EC WILL affect the flash output even if you are in Manual exposure mode.
For example, setting EC to +1 in manual exposure mode will have no effect on the ambient exposure but it will increase the flash
output by one stop. The D4 is the first Nikon body where you can separate the ambient EC from the flash EC, making it work the
same way as the Canon system. More info here :

http://www.nikonusa.com/Learn-And-Ex...th-the-D4.html

The only explanation I can think of for what you describe where two images with the same exposure settings in the metadata look like
different exposures would be if the amount of ambient light changed between the two shots.

Quote:

---

Originally Posted by Mike Milicia

If you are truly in Manual mode (i.e. no auto-iso) and not using flash, then the exposure compensation setting should have
no effect on the resulting image. In other words, if you have two images with the same shutter, aperture, and ISO in the metadata,
then they should look like identical exposures regardless of how the EC is set. However, setting EC WILL affect the metering readout
in Manual mode. For example, let's say you determine your manual exposure settings by spot metering a gray card and zeroing the meter.
That will work fine as long as the EC is set to 0. If you change the EC, it will bias the meter readout by that amount. In effect, the EC in
manual mode changes the meaning of 0 with respect to the metering readout. For example, if you set the EC to +1 and then spot meter
a gray card and zero the meter, the settings you end up with will be one stop brighter than they would be if EC was set to 0. To get the
correct exposure with EC set to +1, you would spot meter the gray card and change the settings until your meter readout is at -1.
This is true for Nikon but not Canon. In fact, with Canon, there is no way to even enter an explicit EC in Manual mode.

But if you are using Nikon flash (prior to the D4), setting EC WILL affect the flash output even if you are in Manual exposure mode.
For example, setting EC to +1 in manual exposure mode will have no effect on the ambient exposure but it will increase the flash
output by one stop. The D4 is the first Nikon body where you can separate the ambient EC from the flash EC, making it work the
same way as the Canon system. More info here :

http://www.nikonusa.com/Learn-And-Ex...th-the-D4.html

The only explanation I can think of for what you describe where two images with the same exposure settings in the metadata look like
different exposures would be if the amount of ambient light changed between the two shots.

---

Being a Canon shooter EC has no effect in manual mode the wheel that controls the EC in auto modes controls the shutter setting in manual did not know it was different with Nikons but we agree that the light changed and no adjustment was made to the aperture or shutter to compensate.

Quote:

---

Originally Posted by Don Lacy

Being a Canon shooter EC has no effect in manual mode the wheel that controls the EC in auto modes controls the shutter setting in manual did not know it was different with Nikons but we agree that the light changed and no adjustment was made to the aperture or shutter to compensate.

---

I am a Canon shooter also but when doing instruction, it helps to know a bit about the Nikon system as well.
I find these particular aspects of Nikon operation to be a bit obtuse. At least they are changing the D4 to give
you the ability to separate flash and ambient compensation. But, as far as I know, The EC will still bias
the meter in Manual mode which I would guess causes more problems than it solves.

I want to thank you for the information you have imparted. Below I have included the two images that I was refering to. The one on the left wrote the following Meta Data to the file.
70-200mm @ 70mm<o:p></o:p>
70mm (in 35mm film)<o:p></o:p>1/800 sec, f/2.8
Mode: Manual
Metering: Multi-segment<o:p></o:p>
ISO: 6400
White balance: Auto<o:p></o:p>
Flash: Off
File size: 69.0MB<o:p></o:p>
Image size: 4256 x 2832
Saturation: Normal<o:p></o:p>
Sharpness: Normal
Contrast: Normal<o:p></o:p>Color profile: sRGB IEC61966-2.1

The one on the right wrote this data:
70-200mm @ 70mm
70mm (in 35mm film)
1/800 sec, f/2.8
Mode: Manual
Metering: Multi-segment
Exp comp: +3
ISO: 6400
White balance: Auto
Flash: Off
File size: 69.0MB
Image size: 4256 x 2832
Saturation: Normal
Sharpness: Normal
Contrast: Normal
Color profile: sRGB IEC61966-2.1<o:p></o:p>
As you can see the files are identical except for the 2/3 change in the EC. I am still confused as I took a series of images as Mike described and they cam out as he said they would. Any more ideas?

Aha ... looks like your issue is WB rather than exposure.
If you bring both of these into Camera RAW and give them the same WB, I bet they will look close to identical.

You are using auto WB and some lighting such as mercury vapor constantly changes color temperature at a high frequency.
At 1/800 second shutter speed, it's the luck of the draw as to what color temperature you will get.
The only way to get consistent color balance would be to shoot at a slow enough shutter speed that things
will even out during the exposure or significantly underexpose the ambient and light the whole thing with
flash if that is an option.

Here's a good explanation of what I think is happening here :

http://www.sportsshooter.com/message...html?tid=20873

Quote:

---

Originally Posted by Mike Milicia

I am a Canon shooter also but when doing instruction, it helps to know a bit about the Nikon system as well.
I find these particular aspects of Nikon operation to be a bit obtuse. At least they are changing the D4 to give
you the ability to separate flash and ambient compensation. But, as far as I know, The EC will still bias
the meter in Manual mode which I would guess causes more problems than it solves.

---

The more I think about EC in manual mode the less sense it makes to me I need the meter reading to be correct for me to place my tonalities within the scene or on the subject where I want them I can see this being a problem for someone learning manual on a Nikon camera since it ads another variable to the equation.

Mike,
I really think you have the problemsolved, but I think you must have missed something. I took both images into Lightroom and changed the white balance on both images to Tungston. The result of the two images are below. They pretty much look the same. I wonder whether if I were to set the WB to a specific number they would look the same, although I can't imagine why the would.
Mac

Yes, I misspoke in the last post. If the color of the ambient light was indeed different at the time of capture,
you need to neutralize the effect in each image which will require a different WB setting on each image.
For example, if the light had a green cast, you would need to boost magenta but if it had a blue cast,
you would need to boost yellow.

What happens if you use the eye dropper tool in Camera RAW and click on the doors which appear to be white?
This should neutralize the color of each image to make the doors white and make everything else fall in line as well.

I think there is definitely a WB issue here but I'm not sure if it entirely explains the results you got.

Thanks all and especially Mike for your input on this subject. I think I know now what caused my misunderstanding. Now I am clear on the subject.
Mac

Florescent light fluctuates in color temp, making it difficult when many lights are present to maintain correct color throughout the entire scene. You can easily see this with the green and magenta areas appearing in your image. I find it best in these conditions to create a custom WB setting. You will most likely still have to selectively color correct a few areas within the image.

NIK Color Effex Pro 4's White Neutralizer filter will do a good of negating the color cast in your image.

Chas