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Shutter Speed, Aperture and ISO

Digital cameras are based on a sensor that reacts to the light reflecting off the subject of the photo you are taking. A certain amount of light is required in order to get a good shot, and that optimum amount of light is basically the same in any situation.

The three things we have to play with to adjust the amount of light are shutter speed, aperture and ISO.

Shutter speed and aperture are closely related. If you increase the aperture (lower F-Stop number) more light gets to the sensor, so the shutter speed has to be increased to adjust the amount of light. Conversely, if you choose a small aperture (bit F-Stop number) then the shutter will have to stay open longer to let in more light. Think of filling a bathtub. If you open the tap all the way (aperture), the tub will fill in less time, and you will turn the water off sooner (shutter speed).

In order to get a good exposure, you need the right combination os aperture and shutter speed. Most cameras have settings where you can adjust one and the camera will automatically adjust the other to compensate and give you a great shot every time. If you have a more professional camera, you may be able to override this feature and choose both manually, and alas, some point and shoot models give you almost no freedom. I have one model that has no aperture settings at all.

In terms of exposure, a narrow aperture/slow shutter speed will give you the same result as a wide aperture/fast shutter speed combination, but varying the aperture also affects the depth of field (DoF) or how much of your subjects background will be in focus. If you are trying to achive a blurry background like in our cherry blossom shot above, you will want a narrow depth of field which can be achieved by choosing a wide aperture setting (low F-stop number), or if you can’t control that, and fast shutter speed, which will force the camera to change the settings to increase aperture.

ISO used to indicate the sensitivity of the film you were using. A high ISO film was more sensitive, and needed less light. Now that most of us are using digital cameras, the ISO setting is actually just a simulation. Increasing the ISO number will cause the camera to have a higher shutter speed which may result in a small depth of field, but use it in moderation, as you may see more digital noise with a highter ISO (that awful ‘grainy’ effect)

Once again, if you want to achive that ellusive blurry background:

Thanks to Elizabeth Laurel for the great shot of last spring’s cherry blossoms!

Controlling Depth of Field With a Pocket Camera

I’ve covered the problem of controlling depth of field with a pocket camera once, but found some interesting information since then.

The idea in controlling depth of field with a pocket camera, or an camera, is to create a photo composition where the subject is in sharp focus, and the background is blurred. This produces a clean result that draws the eye to the subject without compromising the richness of color in the background.

This type of photo composition is normally achieved by adjusting the aperture, or f-stop, and the actual distance to the subject. A larger aperture (smaller f-stop number) and shorter focal distance will result in a narrow depth of field and serve to produce a photo composition with the desired effect.

This is all very well and good with a proper SLR, but sadly, most pocket cameras have such a tiny lens that it isn’t practical to change the aperture, so there are no f-stop settings.

There is a theory that controlling depth of field with a pocket camera is possible by zooming up on the subject, but in actuality, if you zoom up on the subject, you will have to step back and increase the distance, so the depth of field remains essentially the same. There is some merit in using the macro setting and making sure the background is some distance away from the subject, which will work to some extent for flowers and other small objects, but of course wouldn’t be practical for a larger photo composition such as a portrait.

As I mentioned in an earlier post, pocket cameras are set to focus on as much of the frame as possible. In other words, it’s set to have the largest possible depth of field, which essentially renders controlling depth of field with a pocket camera impossible.

Cell phones, on the other hand, are usually set to have the sharpest possible focus for any given object, and have a shorter depth of field. This photo was taken with a Japanes Panasonic cell phone (905i) with a 5.1 megapixel camera. I’m not familiar enough with i-phones to know if they would work the same way. Perhaps someone who has one could comment on this?

Photo Critique

Welcome to the Photo Critique corner of Photo Lifestyle dot com.

I recieved this request for a photo critique from Jade Mayari this morning. What a precious baby photo! Here’s what Jade had to say about it:

Here is a baby photo of my daughter laying on a blanket and the sun was not really out that day and it wasn’t overcast either and it made the picture come up better than I expected. It was taken outside with a Kodak Easyshare 4.0megapixel camera but we used the outdoor setting and possibly that’s what made the colors so vibrant? I love the colors in this photo and it’s one of my favorites.

Indeed. I looked up the Kodak Easyshare 4 megapixel and discovered that while some people are unhappy with the slow start-up speed, it focuses quickly, and produces the brightest colors of any pocket digital camera. The new model of the Kodak Easyshare is integrated with Wii for easy storage and sharing, and has a very reasonable price tag. Good camera choice, Jade!

The colors in this adorable baby photo are brilliant, and it’s obvious this kid is full of life. The removed shoe and tousled dress show she’s been squirming big time, and she looks very happy indeed to be outdoors in her colorful clothes and blanket.

As to the photo critique, I feel a bit uneasy about the angle I find myself looking at this photo from. In fact, when I first saw it, it seemed that the subject was mildly upside down, and I caught myself tilting my head to one side to look into the baby’s face.

Here’s the same picture cropped to a more pleasing angle. It’s not a total solution, as I’ve had to hide her precious pudgy feet, but you can see that it would have been a better picture if Jade had just twisted the camera a tiny bit before squeezing the shutter.

One important component in photography that is missing from this photo is depth of field. Depth of field relates to how close and and how far the camera is able to focus, but it also means simply how much close and far you’ve added to your composition. This photo’s basically two dimensional as the baby is on a flat surface, and the photo is taken from a rather high angle. The green grass is so bright and beautiful, it would have been lovely to have a bit more of it, and have some close up in the foreground, and a background of green as well. This could have been achieved by simply kneeling down in the grass, taking the picture from a 45 degree angle, and zooming out a bit to show more grass in the photo. This would have added a three dimensional depth of field, and made the photo a real contest winner.

Next time your in the mood for snapping a baby photo, I’d recommend taking three pictures instead of one. One from above, one from a 45 degree angle, and one from much lower down, almost at the baby’s level to achieve a profile with large grass blades in the foreground. I think you’ll be surprised by how much more you like a photo with more depth of field.

Thanks for the great photo, Jade, and congratulations on your purchase of the Kodak Easyshare 4 megapixel camera. It looks like it was just the right camera for you!