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Tuesday, July 24, 2012

Deep Focus


Focus On Wildflowers • To Print, Or Not To Print • Auto ISO Isn’t Just For Beginners

Labels: How-ToColumnTech Tips
This Article Features Photo Zoom

Achieving sharpness from the foreground to the distant hills requires several images focused at different zones. Canon EF 28-135mm ƒ/3.5-5.6 IS USM lens at 135mm (for a little compression) and ƒ/11 for each of the exposures.

Focus On Wildflowers

Q My wildflower photographs usually fall short. I can't get the whole field sharp, or when I photograph closer up, the backgrounds are always too busy. Do you have any basic techniques to improve my success this season?
B. Norton
Toronto, Canada


A An abundant field of flowers in bloom is a beautiful subject, and one we love to share with others. "You would not believe how many flowers there were; they just went on and on!" If you really want people to experience what you saw, you'll want the entire image sharp from the foreground to the farthest edge of the field. The simplest way to do this is to stop down a wide-angle lens to around ƒ/16 for maximum depth of field. Keep in mind that using ƒ-stops of ƒ/22 or ƒ/32 won't work as well because at those extreme apertures sharpness is lost due to diffraction.


To isolate this single California poppy from the background, a Canon EF 180mm ƒ/3.5L Macro USM telephoto macro lens was used at ƒ/3.5. It's important to position the zone of sharpness on a significant part of the flower.
If you want to approach the image from a lower, creative angle or use a telephoto lens, you can achieve excellent results with a technique called "stacking." Mount the camera on a tripod and compose the scene. The camera needs to be on a tripod and the scene composed. Set your exposure and use manual focus. Then take a series of captures, beginning with the closest area of focus, and refocusing and capturing at intervals throughout the scene in what could be described as slices of sharpness that overlap from front to back. Assemble the images in software that retains the sharp areas and discards out-of-focus parts, rendering a completely sharp composite with essentially unlimited depth of field (no pun intended). There are several options for the software, including Photoshop (www.adobe.com), Zerene Stacker (www.zerenesystems.com) or Helicon Focus (www.heliconsoft.com). Each offers a trial period, so you can check them out before purchasing.

Unfortunately, stacking doesn't work if the wind is moving the flowers about. It's best to photograph early in the morning before the wind picks up. You can use a higher ISO to increase the shutter speed and stop motion, but often this isn't enough. A solution, albeit expensive, is a tilt/shift lens. By tilting the front element, the zone of focus tilts as well, allowing you to skim across the tops of all the flowers with a larger ƒ-stop (ƒ/5.6 or ƒ/8, as an example). Increase the ISO and shutter speed, and you'll have everything sharp from front to back. If I were to buy only one tilt/shift lens, it would be a 90mm (Canon) or an 85mm Perspective Control lens (Nikon).

If you want to isolate one flower from the rest of the field, you need to control the busy background. The quickest way to do this is to use a telephoto lens set to a large aperture. Telephotos from 200mm to 400mm can be very effective. A 70-200mm or 70-300mm zoom combined with an extension tube for closer focus can be a great isolation setup. Keep the aperture at around ƒ/5.6, and be sure the zone of focus is on the most important aspect of the subject. The ideal lens for the isolation technique is a telephoto macro lens. There are a number of 180mm to 200mm macros that actually focus to a life-size (1X) image. With this lens you can lie down at the edge of a group of flowers and capture many compelling isolated flower images. It's a beautiful way to spend the day.
If you want to isolate one flower from the rest of the field, you need to control the busy background. The quickest way to do this is to use a telephoto lens set to a large aperture. Telephotos from 200mm to 400mm can be very effective. A 70-200mm or 70-300mm zoom combined with an extension tube for closer focus can be a great isolation setup. Keep the aperture at around ƒ/5.6, and be sure the zone of focus is on the most important aspect of the subject.


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