This is the third in a multi-part series on Exposure. The first post introduced three corners of the Exposure Triangle – ISO, shutter and aperture. Last week we covered the ISO corner. We will investigate the shutter speed corner next.

I want to give this adequate coverage so we’ll talk about slow shutter speeds today and next week. The following  week we’ll speed up the shutter and look at fast action scenes. Stay with me to “get the whole picture” (sorry – I couldn’t resist).

Choosing the correct ISO should be the first step to ensure the correct exposure (not too dark, not too bright) is achieved while allowing shutter speeds and/or apertures that “work” for the scene. For instance, a sports photographer will work at high ISO to allow fast shutter speeds needed to capture the moment.

For now let’s discuss slow shutters which allow us to capture a wide variety of scenes. They can also be used for artistic effects if we’re so inclined.

But there is a dark side to slow shutter speeds — a villain responsible for more messed up photos than any other. The villain we need to avoid at all cost is camera shake.

If  the camera is moving during the exposure the picture will be blurred. As we slow down our shutter speed more of the camera shake is captured and the condition becomes fatal.

This photo is a prime example of camera induced blur. The photographer (who will remain anonymous) had the camera set at a low ISO while shooting in a dimly lit cathedral somewhere in London.

The camera opened its lens (i.e., aperture) as wide as possible. But it was a dimly lit location so the correct exposure required a 1/2 sec shutter. That’s far too long for a hand-held shot. The camera shake is obvious and fatal.

There is a rule of thumb used to guard us from the villain. We must keep our shutter speed at or higher than the focal length (aka zoom) of the lens. So if you’re shooting at 50 mm focal length — a common value — the minimum shutter speed would be 1/50th of a second.

Violate this rule and the villain will visit leaving you with a blurry photo of  your children.

Check out this earlier post that discusses techniques you can use today to minimize camera shake and keep the villain at bay.

Now that we’ve been warned, let’s look at situations that employ long, slow shutters to good effect.

Landscape photographers shoot at low ISO with very small apertures. Low ISO minimizes photo noise as demonstrated in last week’s post. A small aperture ensures everything, foreground to background, is in focus.

Small apertures and low ISO push the camera to very long shutter speeds to achieve proper exposure. That’s why a landscape artist will spend several hundred dollars on a sturdy tripod to keep the camera dead still during the long exposure.

In both photos above the aperture was small (f/16+) and a low ISO was intentionally used. This combo led to shutter speeds of as much as 20 seconds. A tripod was used for both.

So how does this apply to you?

Your camera allows you to choose picture modes. These modes have very common symbols. Landscape picture mode is depicted as the outline of a mountain.

When you shoot in landscape mode your camera will use a small aperture. If you are not using a tripod you will need to bump up your ISO to ensure the shutter is fast enough (1/50, 1/100, ….) to minimize the impact of camera shake. If you forget you’ll be visited by the camera shake villain.

Macro photography has similar needs. The macro picture mode on most cameras is identified with the symbol of a flower. If this is something you would like to try let’s tie it in with our Exposure Triangle and slow shutter discussion.

Very small apertures are used in macro photography for the same reason they are used by landscape photographers. The goal is to get everything in sharp focus.

In the photo above I used a tripod and got very close to the flower. That necessitated a small aperture (f/20) with a shutter approaching 1 sec.

To be technical (for a second only),  macro requires an image the same size or larger than the object. The photo above would be consider close-up photography. Let’s forget about that for now. We’ll cover macro photography in more detail in a future post – stay tuned.

OK – another long post with, hopefully, some useful information. Let’s pick this up next week with some more examples of how slow shutter speeds can be used in artistic ways.

Feel free to comment or show off some of your own compositions that illustrate this tip. In the meantime, stay tuned because more Tuesday Photo Tips are right around the corner. Better yet — be updated automatically by “friending” our Facebook site.

PS - This is one of dozens of photo tips in our continuing Tuesday Photo Tips series of posts. There  are other resource articles on our site you may enjoy covering basic and more advanced photography topics. There are also tips covering topics such as preparing for family or infant/child portrait sessions. If you would like a topic covered just jot it down in a comment or send us a note.