A Focus bracketing / stacking experiment

This post is not my usual Central Florida Photo Op entry. Instead I want to cover a technique and some software I’ve been experimenting with.

One macro photography challenge is to get the desired portions of the subject in focus without using such a small aperture that the image quality is degraded by diffraction effects. One solution is to combine multiple images focused at different depths within the frame to extend depth of field. In this post I’ll talk about how to do this, including software that can be used to automate the process. I’ve posted one focus bracket image before in this blog. That image was created manually. Using software to help is much easier.

Note: double click any of these images to view them on Flickr, where there is a larger version available. You can also visit the entire set at this link or view a slide show at this link.

Dry Backlit Orchid - focus bracket at f/8Back-lit Orchid – 15 separate captures at f/8.

As with all macro photography, good technique remains important. Focus bracketing will not make up for poor composition and exposure or sloppy camera handling. But for stationary subjects focus bracketing can give the photographer complete control over depth of field, background appearance / bokeh, and help optimize image quality. I used a program called Helicon Focus for this experiment. I think you can accomplish the same thing using Photoshop CS4, but I don’t have this latest version, so I haven’t tried. Helicon Focus is available as a fully functional 30 day trial download, so you can experiment with it too.

The Helicon Focus web site has a lot of information on how to use their software. To learn more, browse these links:

Here are some of my additional hints based on what I learned while evaluating the software.

  1. Use good macro and general technique
    • As for any type of bracketing, a sturdy tripod will help make sure all images are aligned.
    • Use a cable release or remote so you don’t jar the camera.
    • Use the mirror lock up function on your camera with low shutter speeds
    • Know your lens and camera.
      • Which aperture has the best image quality? (Usually ~ 2 stops down from wide open)
      • Make several test images at a different apertures. Use them to select the aperture to use with the focus bracket series. You can also use one of these later if you like the background bokeh better than in the focus bracket result.
      • Where does diffraction start to affect the image quality? (About f/11 for full frame cameras and ~f/8 for APS C size sensors
      • Don’t forget about composition.
        • Eliminate unnecessary image content
        • Remember (or not) the Rule of Thirds
        • Isolate the subject and make sure the background isn’t distracting (e.g. bright spots)
  2. When you’re ready to start the focus bracket capture, set your camera in manual focus and exposure modes. Also set your camera to a manual white balance, or do this post capture if you use RAW.
  3. Make a series of captures working from far to near and varying the focus slightly closer for each one. I found that the smallest movement of the focus ring that I could make worked best.
  4. I saved the images in RAW format and processed them through Capture NX2 in batch mode to apply the same pre-processing edits (overall lighting adjustment, some highlight recovery, a little dodging and burning and some basic sharpening) to each photo. I also used NX2 to convert the RAW images to TIFF format.
  5. Then I ran the TIFF images through Helicon Focus. By the way, it is Intel i7 aware and so it runs pretty fast on my iMac. The only change I made to the default settings was selecting Lancos8 resample quality.
  6. My resulting composite image had a few areas that could be improved by cloning from one of the source images. Helicon Focus supports this with a “resampling” mode which allows you to clone from any of the source files into the final before saving.
  7. Once I had the final composite output saved, I opened it in Photoshop. Since I liked the bokeh of the f/36 image, I cloned from that background into the composite – and I was done, except for importing into Lightroom where I added some clarity and adjusted contrast.

Here’s a series of images to illustrate.

Wet Backlit Orchid at f/5.6Wet Back-lit Orchid at f/5.6. At this aperture (2 stops from wide open) the lens optical quality is very good, but the depth of field is shallow. Parts of the flower and the stem are not in focus. The background is completely blurred out.

Wet Backlit Orchid at f/36Wet Back-lit Orchid at f/36. At this very narrow aperture, the depth of field is maximized. The out of focus leaves and background are pleasing. But the small aperture is causing diffraction to degrade the optical quality of the capture.

Wet Backlit Orchid - focus bracketWet Backlit Orchid – focus bracket. In this composite photo made using the Helicon Focus program and 16 individual captures at f/5.6, the depth of field covers the entire flower and stem and the background is completely blurred. The optical quality is improved since the wider aperture does not suffer from diffraction.

Wet Backlit Orchid - focus bracket with small aperture backgroundThe final image: Wet Back-lit Orchid – focus bracket with small aperture background. You can completely control the background. If you prefer the bokeh / background of the f/36 image, selectively clone it into the focus bracket image.

Conclusions: Focus bracketing is a useful technique that can give photographers a tremendous degree of control over depth of field in situations where the subject matter is still and there is time to set up, capture and process for it. If you add a manual step to the final output, you can selectively enhance the bokeh. Helicon Focus runs well and does what it is supposed to – make this process easier.

©2010, Ed Rosack. All rights reserved.

2 thoughts on “A Focus bracketing / stacking experiment

  1. I did try the focus bracketing function in Photoshop CS4 with very poor results.

    For close in subjects like this flower, Helicon Focus seems to handle the change in magnification at different focus distances while Photoshop does not.

  2. This seems like a neat way to create unique images. I have seen at least a couple of others that apparently did use photoshop. That seems like much more work though.

    In Oregon last year I happened upon a gallery where a guy had done this with some irises, with a black background. Evidently it was 150 shots. The result was just beyond belief. Like Avatar, but still life.

    Thanks for this great writeup. I hope to make time one of these days to try this out.

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