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Tuesday, February 28, 2012

Max Depth Of Field

Stacking Ghosts • Film Scanners And The Year Of The Lion • Choosing B&W Print Media

Labels: ColumnTech Tips

This Amazon boa was photographed in the studio using a Canon EOS 5D and a Canon EF 180mm ƒ/3.5L macro lens. I quickly took four shots at ƒ/16 and 1⁄60 sec. from a tripod. Each image captured a different plane of focus, slicing through the image from front to back, and then all four images were combined in Helicon Focus.

Stacking Ghosts
Q I've tried macro image-stacking software repeatedly, but have had terrible luck with it. When I change focus points, the image size changes slightly. After enough of these resizings, the composition has changed considerably. When I try to blend the images together, either in Helicon Focus or Photoshop, I get a really bad image with lots of ghosting effects. I'm shooting on a tripod and using the Canon 100mm ƒ/2.8 macro lens. When shooting, I'm only adjusting the focus ring on the lens, with no other movements.
J. Rusk
Via email

A Precision matters when seeking unlimited depth of field. The basic idea is to increase the overall sharpness of a photograph by capturing several images with overlapping areas of focus, then compositing the images into a single image in software that retains only the sharp elements of each capture. You can use the technique for any unmoving subject, from landscapes to high-magnification snowflakes. Note that even the slightest amount of movement will make the process impossible, so whenever possible, I work in the still of the morning and bring macro subjects into a sheltered area or the studio.

For several years, I've been a big fan of using Helicon Focus (www.heliconsoft.com), Photoshop CS5 and its Blending Modes (www.adobe.com) and Zerene Stacker (www.zerenesystems.com), but I'm here to tell you that not every attempt will work. Sometimes one program will do a better job than the others on a particular set of captures, so if one fails, I'll try compositing again with another. My favorite at the moment is Zerene Stacker, which seems to offer the best results with the work I do. But all of the software programs are pretty simple to use and remarkably consistent, so the best approach is to improve the captures you're providing to them. Here are some tips that might help you achieve a better success rate.

Composition Counts. If a foreground object is prominent in your composition (such as a single flower larger than those at the back of the group), be aware that the object will "bloom" larger as it's thrown out of focus when the photographer moves the focus past it. The out-of-focus foreground object may then obstruct elements of the background. Blooming is a significant cause of the ghosting you mention. Sometimes it's just not possible to properly render particularly complex compositions with expanded depth-of-field techniques. In macro compositions, it sometimes helps to pull back on the magnification a bit to give some room for cropping the final composite to eliminate some edges that might not line up, a problem that shows up more often in the CS5 version.

Adjusting The Focus. As you note, working from a tripod is imperative when attempting expanded depth-of-field techniques. Set your focus to manual. Choose an ƒ-stop that maximizes lens sharpness (usually ƒ/8 or ƒ/11). Frame the image, then focus on the front elements of the composition and take your first capture. Adjust the focus slightly to bring the next "slice" of the image into sharp detail, overlapping about 30% with the area of focus in the first capture. I generally use more images than may be necessary (more overlap) to make the transitions less severe between each slice of focus. Continue to work through the composition until you've covered everything you want to render in sharp focus. Then do it again so you have at least two sets of images to work with later at the computer.

Moving The Camera. For macro photography, I use the Canon MP-E 65mm macro, Canon 100mm macro and Canon 180mm macro lenses. Especially with macro work, simply adjusting the lens focus incrementally isn't usually the answer because it's just not precise enough. I often work with a macro focusing rail that moves the camera/lens precisely in measurable, incremental amounts to capture the slices of sharp focus.

Moving The Subject. For truly high-magnification photographs of very small subjects, such as butterfly wing scales, crystals and snowflakes, I put the subject on a glass slide on a movable stage, mount the camera above it on a copy stand, and light it from above and below with LED lights and/or flashes. I view the composition on my laptop computer using Canon's Live View feature. The focus adjustments are made by moving the stage in minute increments, closer to or farther away from the fixed camera/lens. The camera is fired from the computer.

Film Scanners And The Year Of The Lion
Q A few years ago, I contacted you regarding scanners for 6x7 and 35mm images. At the time, you recommended the Nikon 9000 ED and 5000 ED Super Coolscans. I delayed on the purchase in the hopes the next-generation scanner would give more resolution; when I finally pursued the purchase, I found the Nikons were no longer manufactured. Any new recommendations?
J. Murtha
Via email


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