Saturday, May 2, 2009

On The "Technical" Side...

I attended about a half a dozen classroom sessions at the Foto Festival. There were so many choices, but as I made my selections I had one primary goal in mind. I wanted to learn more about achieving good exposure. I'm happy to say that I came away with a better understanding and a lot to practice with.

As a photographer, you have a concept of what you want to convey or capture in an image. But without an understanding of exposure, it becomes an issue of luck. I definitely have a problem with nailing my exposure more often than not. But I intend to put these points into regular practice and hopefully with time, they will all become second nature.

The number one tip I learned (which I already do) is to put your camera in manual. As long as you're shooting in aperture or shutter priority, you are not in complete control of your exposure. Your camera can make a very good estimation of what you're going for, but it is programmed to make white gray. If you want to stay in one of these priority modes, learn about EV and how to use it to compensate.

A stop is a halving or doubling of light. If you shut down one stop, you have halved the light that will hit your sensor. If you move up a stop, you double it. One click of your shutter speed, aperture, or ISO is not necessarily one stop. In my camera, it is set that each click is 1/3 of a stop. So, I need to make 3 clicks in a single direction to adjust my exposure one stop. The stop adjustment can be made using a combination of ISO setting, shutter speed and aperture depending on what the photographer is trying to achieve with the image. (Stop action, bokkah, etc)

Expose for highlights! If your highlights are blown out, they are gone and that often blows the image. In bird photography, you cannot blow out white highlights and capture feather detail in the white end of the spectrum. I had a lot of trouble with this, I was not as sensitive to the location of the hottest highlights as I needed to be. This is where the histogram becomes invaluable.

The histogram is a wonderful tool. I would check my histogram on many of my images, but until now I didn't take advantage of some of the valuable information it provides. Your histogram shows you the distribution of tone in your image. If it is pushed to the right, you are going to have a light image. If there is a spike on the far right, you are going to have blown highlights and you need to stop down. I can see that even a small spike on the right indicates that something is overexposed in the frame. It might be just the top of a bird's head, or a peak of light between leaves. In that case I might want to stop down a fraction of a stop to correct that.

Stop down = increase shutter speed, increase aperture, or decrease ISO. Any of these actions will reduce the amount of light reaching your sensor.

If your histogram is pushed way to the left, your image will be very dark or underexposed. This is preferable to overexposed as the details may well exists in the shadows and can be revealed in the editing process. However, they may be a lot of noise in the shadows as well.

A histogram shaped like a wide U means that your tones are concentrated in both highlight and shadow. This is a tough exposure situation. I would probably shut down to accommodate the highlights (hoping to retrieve detail in the shadow), change my angle or composition to attempt to remove hot highlights from the scene, or wait for the light to change.

A histogram that has a skinny spike in one area is not a bad exposure (unless it's all the way to the right or to the left). I believed that a good exposure was indicated only by a nice bell curve, and a spike was bad. This is not the case. It means that all the tones in the scene are concentrated in one range. This is the type of histogram that would often occur photographing a bird on the beach or in the sky. Most of the tones in the scene are the same (the spike) with the tones of the bird being spread throughout the rest of the histogram.

Learning to get the right exposure is a real challenge. The beauty of digital is that we can review an image instantly and the camera provides us with a histogram for exposure evaluation. We're not taking home a roll of film and crossing our fingers while we wait for processing. We're all destined to miss the mark again and again, but with practice, we can develop an eye for proper exposure. I believe it's part of learning to see with a photographer's eye. I intend to go out and shoot a lot in less than perfect conditions, the challenge being learning to see the exposure that will make the best image.

I want to take it to heart that a day of shooting, with no great shots is not necessarily a bad thing. Yeah, those days are disappointing, but I have to look at them as an opportunity to learn. I'd like to share a wonderful post I read recently by Marc Graf on Embracing Failure. After reading this essay, I will never look at a "bad" day of shooting the same way again.


MariesImages said...

I am very impressed, Kat, with your post & what you've brought back to our community challenge blog.
Thanks for sharing your knowledge & experience with us!!

Clyde said...

Thanks for clearing up some fuzzies that I would not have if I had been paying attention years ago. Some things become second nature after 50 years but they still need reviewing. I think I'm on the down slope of a learning curve where you start forgetting stuff everyday.