Sunday, August 28, 2011

Perspective And Long Lenses

Long lenses definitely have their place when photographing distant subjects. Mention wildlife or sports photography and one instantly thinks of enormous telephoto lenses capable of photographing insects from a distance of one mile. Sorry to disappoint, but there aren't many lenses with that level of magnification.

This shot was taken in Richmond during a sand lot sporting event. Exposure was F 5.6, 1/2000 second, ISO 200. The lens, a 70-300 variable aperture lens, was set to 5.6 which is nearly wide open when the lens is set to 190mm, as it was in this photo. Megan, in the foreground, appears to be touching her brother Brandon, even though they are separated by a distance of nearly 3 feet.

Long Lens Perspective: Long lenses are believed to have a "flattening" effect, which is to say they bring the background closer to the foreground. I contend that it's the distance, not the lens, that creates the effect.

To illustrate, I mounted a 18-200 zoom lens on a D1X body and set it to 18mm. The camera was mounted on a tripod and the camera leveled with Kermit. This first image was taken at a distance of 2 feet.

All  of the images would be photographed at 1/6400 at F 5/6 at ISO 800. 5.6 was chosen because it was the largest aperture available at all focal lengths. No exposure adjustments were made, but the images were cropped square.

After the shot was made, the tripod was moved along a reference line in the pavement.

For this first pair of photos, I doubled the distance to 4 feet. The photo on the left was with the lens set to 18 mm. I then increased the focal length (zoomed) until Kermit again nearly filled the frame from top to bottom. Notice the scale of the background when compared to Kermit.

For this second pair, the distance was doubled again. The shots were made at 8 feet with the left shot at 18mm and the right shot zoomed in. Again, the background appears larger and less distinct than before.

This final pair of shots was made at 16 feet. Again, the left shot was at 18mm, while the right was made with the lens at 200mm, the longest focal length available. Now the background is barely recognizable, and Kermit is clearly the focal point of the photo.

Foreshortening: Foreshortening occurs when the background is rendered smaller in size when compared to the main subject in the foreground. While it is obvious that distant objects should be smaller, it is easy to overlook problems associated with foreshortening, especially when working at short distances.

If you look closely at the first image of Kermit (taken at 2 feet), you'll see that his feet appear to be as large as his head. In the image on the right, taken at a distance of 16 feet, you will see that the relative size of Kermit's foot is smaller than what we might expect. These two images illustrate foreshortening at both extremes. You need to remember that it's the distance to the subject that creates the disparity between the images and not the focal length of the lens.

This problem is generally associated with wide angle lenses, since they are often used whenever it is necessary to photograph a wide subject at close range. This shot, made during San Francisco's Carnaval in 2011, shows a group of dancers standing on the street. I used a Vivitar 283 flash mounted on a monopod, triggered by an extension cable passing through a Wein Safe Sync. The exposure was 1/2000 at F 8.0, ISO 200, which gave me an image that was underexposed by one stop. Ooops. Click on the image for a closer look.

If you look closely, you will notice that the fourth dancer from the left has her arm outstretched toward me. You will notice that her hand appears disproportionately large when compared to her head. This is how foreshortening sneaks up on you when you're in a hurry. The group's choreographer thought this would be the most theatrical pose, but as you can see, it doesn't work when you are forced to shoot at close range.

If I were to photograph this group again, I would have had them all position their arms nearly touching the dancer beside them. This would keep the hand within the same image plane of the face, minimizing the effects of foreshortening. 

Of course, if we did everything perfectly 100% of the time, our lives would be totally boring. At least, that's what I'm telling you.