Being the control freak that I am, I quickly made the change from shooting in fully automatic to fully manual. My rationale was that if I let the camera make the choices and it chooses poorly, then there is little I can learn from to get better the next time. If *I* make all of the choices and take a poor picture, then at least I can learn from my mistakes and strive to do better next time.
There are hard and fast rules one must understand when setting these variables yourself, but fortunately they are simple ones, too. Every time you double the shutter speed, it doubles the amount of light that reaches the sensor at the back of the camera. Similarly, every time you double the ISO value, the sensitivity also doubles. And, yes, you guessed it, every time you go up one f/stop (the aperture is measured in f/stops), this also doubles the amount of light. So you can see, by creatively doubling one variable and halving another, you can effectively control what kind of picture you will have.
Somewhere along the line, someone with way too much time on their hands decided to analyze thousands (if not probably more) of photographs to determine what the average light reflectivity was in each photo. After what I'm sure was a mind-numbing effort, it was determined that the average light reflectivity was 18%. This meant that of all the light that struck the subjects in the photographs, only 18% of that light was reflected off of them and into the camera. Thus, the light meters built into all cameras from that point forward were set up to expect that every exposure would contain 18% reflected light.
In a perfect world, this would be great. But, as I'm sure everyone out there knows, we do not live in a perfect world. If I were to send back all of the food that didn't meter a perfect 18%, I would be a very hungry food blogger. Fortunately, a relatively easy solution exists to help out with this problem. Most (if not all) camera stores carry what are called "Gray Cards" which is a large cardboard (usually) rectangle that ... wait for it ... reflects exactly 18% of the light that strikes it. The theory goes that if you position the card where your photographic subject will be, fill the LCD screen with the gray card by zooming in, and adjust the three variables until your exposure meter reads "0", you should have a proper exposure. Now the only step left is to remove the gray card and snap the photo at the preset exposure levels and et voila! A perfectly exposed picture.
Hmmm ... don't believe the hype. At lunch today I decided to try this out before my first course arrived at my table. I leaned the gray card against my glass of water and after setting the ISO to 100 and the aperture to f/2.8, I adjusted the shutter speed until the exposure meter marker sat exactly at zero. According to the exposure meter, the correct shutter speed was two full seconds. Okay, a little long given the light levels where I was sitting, but hey, this is SCIENCE(tm)! It is accurate and repeatable! Additionally, the live histogram on the LCD panel had a spike right in the dead center, just as it should.
When my soup arrived, I removed the gray card and placed the cup of soup exactly where my water had been on the table. Here was the shot my camera took:
ACK!! Clearly this looked overexposed on the LCD panel and when I checked the histrogram in picture review mode, my suspicions were easily confirmed. The graph was heavily bunched up on the right side of the graph and spiked up to the top.
Scratching my head, I decided to start reducing the shutter speed until I got a good histogram reading (where it was evenly spread from dark to light) and took another shot, this time with the shutter speed being at four-tenths of a second:
Hey, look a that! It's actually a cup of soup, not the light from the nuclear bomb that just detonated outside the window! I would expect that at the first exposure setting, there might be a tick up or down on the actual shutter speed, but at ONE-FIFTH the original setting ... either I'm doing something horribly wrong or all this gray card metering before taking a "proper" exposure is just bullshit. Strong words, I know.
Honestly, the entire reason for going through this step makes sense to my science addled brain, but with results like this? Well, I clearly hope that I have just made a mistake in the process i used to utilize the gray card.
If anyone out there has any ideas of why this failed so spectacularly, I am open to any and all suggestions. For now, I'm going to continue to base my exposure settings on the live histogram on the back of my camera. While it isn't foolproof, it also has produced the most consistent results to date.
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