OP Home > Columns > Tech Tips > Slicing Up Depth Of Field


Tuesday, April 1, 2008

Slicing Up Depth Of Field

Formulas And Focus • Size, Weight And Will it Float? • From JPEG To RAW • Charging Overseas Without A Charger • Bifocal Focus

Click Images To EnlargeThis Article Features Photo Zoom
tech tips
Image of flowers at the Denver Botanical Garden taken with a Canon EOS 5D and processed using Helicon Focus Softwa

Formulas And Focus
I shoot a lot of wildflowers and have tinkered a bit with Helicon Focus Software (www.heliconfocus.com). The main objective is, of course, the soft background with a sharp subject. Do you have any formulas for the number of slices at various magnifications? I use a Really Right Stuff focusing rail and a Canon 90mm tilt/shift with and without extension tubes.
D. Nelson
Via the Internet

Helicon Focus is a software program that offers photographers unlimited depth of field, and it’s especially useful with macro subjects like flowers. With the camera on a tripod, the photographer takes a number of overlapping shots, adjusting the focus to achieve a set of sharply focused “slices.” The program processes the images to retain only the sharpest version of each part of the image and assembles a final composite that’s completely sharp. The key to using this program to retain a sharp subject with an out-of-focus background is to never offer a slice with the background in focus. To achieve this, use a fairly large ƒ-stop (ƒ/8) so the subject can be rendered completely sharp with a series of images, with none of the backgrounds in focus. As you preview the image for each slice, remember the viewfinder is showing you the field of focus attainable with the lens in its default widest aperture—less depth than what the set aperture will yield. Use this preview to determine the points of overlap, and your slices taken at ƒ/8 will give you a full set of sharp overlapping images. I don’t use any particular formula to choose focus points other than the process just described. When you get to the last shot with your subject in focus, use the depth-of-field preview to be sure you have the desired background effect.

The focusing rail you describe will work well for this series of images, but the 90mm tilt/shift wouldn’t be the lens I’d use to photograph wildflowers with an out-of-focus background. A longer telephoto (180-300mm) would be better, as it allows you to be selective in choosing sharp and soft elements. The 90mm tilt/shift, coupled with Helicon Focus, would be ideal for sharp rendition of a field of flowers from a close foreground to a distant background.

The attached photo shows a group of flowers totally in focus, while the background is completely out of focus. The image was accomplished using a Canon EF 180mm macro lens and six captures focused on different points in the flowers only. The six captures were processed in Helicon Focus.

Size, Weight And Will it Float?
What are the advantages of a D-SLR over a quality digital compact camera? I’m planning a photo safari to Africa (Malawi and Zambia). Most of the shooting will be from vehicles with other people in them. In Lake Malawi, I have the option of underwater photography. My photo equipment budget is about $2,000, and less is always better. I’d like to capture the best-quality images my budget allows. I’m looking at the Panasonic Lumix DMC-FZ18 for its long lens (28-504mm, 35mm-equivalent), image stabilization, small size and weight, and low price. I’m not sure the advantages of a D-SLR justify the price tag, size and weight. Could you explain some of the more important advantages of the D-SLR?
L. Rhoades
Hawaii, Via the Internet

It all depends on how you’re going to use your images. If your intent is to make smaller prints (8½x11), post images on the Internet and create digital slideshows, the compact camera will do an excellent job. If you plan to make larger prints, and possibly submit them for publication, then the larger sensor of the D-SLR and the resulting digital file are necessary. Other advantages of the D-SLR in shooting wildlife are capture speed (up to 10.5 frames per second) and a shorter time lag between activating the shutter and recording the image. There are many reasons professional photographers and advanced amateurs carry heavy tripods and camera bags—they need to make large prints or provide image files that are marketable in the professional realm. However, with your budget and preference for light weight and small size, the compact digital is a good choice. Achieving the same range of focal lengths in a D-SLR would take a camera body and several lenses.

If you want to do underwater photography, the compact digital camera has another advantage: the availability of underwater housings at a reasonable cost. The particular camera you mentioned, and numerous others, also have a movie mode that can be useful.

> Visit www.geolepp.com.


Add Comment


Popular OP Articles