Why does the exposure vary in these Nikon flash photos?

Question

The following 4 photos were all taken with a Nikon D300 at 1/250s, f/5.3, ISO-400, in shutter priority mode, with the on-camera pop-up flash. The only difference between them is the exposure bias, which varies from -4EV to +2EV. You can clearly see that the four pictures get brighter, despite having the same exposure settings.

Can you explain how/why this is happening? I have come up with a few possibilities, but I don't know which (if any) is actually correct:

• Is the camera adjusting the output of the flash to compensate for the exposure bias? This seems like the most likely solution to me, based on how the images look, but my understanding is that exposure bias was supposed to control the amount of ambient light in the scene, while leaving the flash alone, whereas flash exposure compensation is supposed to control the power output from the flash. (Flash exposure compensation remained constant for the four images).
• Alternately, is the camera applying some sort of automatic lighting correction in post-processing after the images were shot? (These images were all taken in JPEG mode, not as Raw).
• Is there some other effect at play here that I don't understand?

Edit I've copied-and-pasted the relevant exif data, extracted by exiftool, for the photos. The data is identical in all important fields (I checked using diff), except for the Exposure Compensation and Exposure Difference fields (I don't know what the latter means):

Camera Model Name               : NIKON D300
Exposure Time                   : 1/250
F Number                        : 5.3
Exposure Program                : Shutter speed priority AE
ISO                             : 400
Flash                           : On, Return not detected
Flash Type                      : Built-in,TTL
Flash Exposure Compensation     : +2/3
Active D-Lighting               : Normal

The Exposure Compensation and Exposure Difference fields for each image, from top to bottom is as follows:

Exposure Compensation           : -4
Exposure Difference             : -0.3Exposure Compensation           : -2
Exposure Difference             : -2.5Exposure Compensation           : 0
Exposure Difference             : -4.4Exposure Compensation           : +2
Exposure Difference             : -6.6

Asked by David

Answer

With Nikon, Exposure Compensation affects the overall exposure, including any automatically metered flash, while Flash Exposure Compensation (when available) affects only the flash's contribution to the overall exposure.

If the scene weren't essentially a flat plane (there isn't much depth to the scene at all), you could use Exposure Compensation to bring down the entire exposure, then boost the flash exposure to correctly expose your main subject. That would isolate the subject from the background. (The opposite can be set in theory, but it won't work unless and until somebody invents a "flash" that subtracts light from the ambient exposure.) More often, though, you'd use the Exposure compensation to compensate for the tonality of the scene (bumping it up for scenes consisting mostly of lighter tones or lowering it for predominantly dark scenes), then independently adjust the flash (usually downward) to add the desired amount of fill.

Note that with these pictures, there isn't much contribution to the exposure from ambient light at all, so if you had set the Exposure compensation to -1 EV and the Flash Exposure Compensation to +1 EV, you would have gotten pretty much the same picture as the normal exposure.

Answered by Stan Rogers

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How can I get nice, vivid colors in food photography without blown-out brightness from the flash?

Question

Whenever I click pictures of people and food using flash, the whole picture becomes bright. When I click without flash, the camera takes in the light from the surroundings and gives me a monotonous and dull colour pattern, particularly when photographing food..

I was trying to capture photos that retain the colour pattern but make the colours more vibrant. Is it possible to achieve this without h post-image processing via editing software? What camera settings or technique should I use to improve my results?

My P & S Camera is Samsung i8.

Answer

I'd suggest you look at using exposure compensation. If your pictures are too bright, then go ahead and use the flash, but turn the exposure compensation down (-.5 or -2/3 for a start). This tells the camera you think it's too bright and it will adjust down.

You can get very dull colors if the light is too low, or if the flash is too bright and washes everything out. If you get the exposure (brightness) right, the colors should be much more vibrant.

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How does adjusting the brightness on my LCD screen affect the photo?

Question

On my DSLR, there is a setting to adjust the LCD screen's brightness level. If I were to turn this setting up (make the LCD brighter), does this affect the quality of the picture? I would assume that something looks nice at a "brighter level", is going to look darker than I expected once I transfer it to the computer. Is there an appropriate method to compensate for modifying the LCD brightness? (maybe turn the exposure down a stop?)

Answer

LCD brightness affects your perception of the photo, not the photo.

At worst, a poorly adjusted LCD will cause you to make bad settings decisions. Make your decisions based on data in the histogram to avoid such errors.

The goal when adjusting brightness is that white areas emit as much light as a white object would reflect. This means the LCD should be dimmer in low light, and brighter in bright light.

Proper adjustment is difficult to maintain. It's impossible to perfect without hardware. Just stick to the histogram.

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