In this post we will be going back to some really basic stuff, but it bears mentioning as we often tend to forget (or ignore) some of the more basic functions of photography. In this case it is the minimum focal distance of your lens. Here are three tips that will help.
Why the minimum distance, you ask? We'll if you think about it there is no maximum distance. It's not like we get to 'x' number of feet and we can't focus any more. If you look at all your lenses they all max out at infinity. So maximum is not the critical distance. How close you can get is.
If you have ever tried to get in close to your subject and the lens starts going crazy when you press the shutter half way it is because it's trying to focus on something that's too close. Nothing is more annoying than wanting to get focussed and the lens does that back-and-forth hunt and seek dance.
As a rule of thumb the shorter the focal distance the closer you can get to your subject. The closest being with a macro lens. By understanding how close you can get to your subject you understand what you can get away with in composition. Take a telephoto lens as an example; my 70-300mm zoom has a minimum focal distance of about 18 inches. That means the closest I can get to my subject is 1 1/2 feet away. So when I have that lens attached to my camera I need to keep back if I want to get up and close.
So I grab my 70-300mm telephoto lens and patiently work my way closer to the action as the butterflies acclimate to my presence. Since the closest I can get to my subject is a foot and a half I know I can get in tight but still keep a comfortable distance from the insects. The great side effect is the ability to really blur out the background with the shallow depth of field.
Tip number 2: Some variable focal zoom lenses will have two minimum aperture allowances. For example, my 70-300mm has a 4.0/5.6 variance. So at 70mm I can get 4.0 and at the zoomed out 300mm I get 5.6. Some lenses will do the same with their minimum focusing distances too. Check the specifications on your lens to determine focal distances.
Unlike the butterfly image above, the telephoto lens will not be of any use if you are trying to get a wider field of view. A wide angle or fish-eye lens allows you to get all the scene in and can often be used to exaggerate the story.
At the Simsbury Fly-In, an annual auto/air show, I came across an elaborate set up reminiscent of a fifties drive-in diner. I wanted to highlight the 'waitress' but she needed to be kept in context. With my lens set at 30mm I was able to get in close to my subject, filling the frame with her and still have room for the car.
In the image at right I was literally a few inches away from the mannequin. At 30mm it kept distortion to a minimum while taking in a wide area. Because I knew I could get really close with this lens I was able to use its properties to convey the story nicely.
Tip number 3: Some wide angle and most fisheye lenses distort perspectives and round off lines, specially at the edges. The wrong lens on the wrong body can also introduce vignetting at the corners. These issues are not necessarily detrimental to your picture taking and can often be used for great effects. You need to push the boundaries of your lens and physically look at the results to get a sense of what your lens does. Spend time with the lens and experiment.
So you can see from just these two examples that understanding how close you can get is a good way of getting the results you want. Next time you are up and close to your subject and your camera's focus can't seem to lock in, you may be too close.
If you are unsure of your lens' minimums check your equipment manual or go to the lens manufacturer's web site for specifications. Remember that some variable zoom lenses may have variable short distances.
NOTE: The image of the eye is actually a close up of an advertising decal in a window. It was taken on our Stamford Street Shoot meet up.