Digital photography has brought us many multi shot techniques like focus stacking and HDRI. This story is about Focus Stacking, this is a technique that we can use to get a much larger depth of field than we normally get with digital camera's. The most well known is HDRI or High Dynamic Range Imaging. That is a technique that we can use to greatly enlarge the dynamic range of a digital camera. That is necessary because digital camera's do not offer us enough dynamic range in many natural conditions. That's not a problem of digital camera's, dynamic range was definitely not better with old school analog camera's.
A close-up photo normally has a very limited depth of field. This is due to the optical properties of the lens in combination with the chip size of the camera. Photographers try to get around this issue by using large aperture numbers like f22 or even f32. A drawback of using these large aperture values is that the lens is definitely not performing at it's best with these values. Sharpness and optical resolution of the lens is way better with smaller openings like f5.6; but then you have a very shallow depth of field.
Focus stacking is a multi shot technique that you can use to greatly enhance the overall depth of field of a picture. The trick is to take a lot of images of the same subject. After each image the camera needs to be moved closer to the subject. That way you take slices of the subject. Each image has it's focal plane at a different location of the image. You can use small apertures with this techniques, like f5.6. You then use software like Helicon Focus to merge the images together to one image with a very large depth of field.
The opening images of this blog is taken by taking 40 subsequent images. The aperture that was used was only f5.6. The camera was automatically moved 0.10mm closer to the image after each shot. I used my DIY time-lapse dolly to do this. The results in 40mm difference in the focal plane between the first and the last image that was taken.
The following video shows the dolly while taking the images. Note that this is being done completely automatically. The OpenMoco firmware does it all.
The Helicon Focus software analysis each input images and uses some kind of contrast detection algorithm to determine the sharpness. The input images are then stacked into one output images with a larege depth of field. I have not altered the images that came out of the camera in any way. Helicon Focus just used the RAW images that came out of my Nikon D700. The output of the analysis can also be used to create a 3D model of your image. The following short video shows the 3D model that was generated.
Here is one other example of the same flower. This images is based on 50 shots. Aperture f5.6 was used again. The total movement of the focal plane was 50mm, 0.1mm after each input image.
Note that you need some post production work at the edges of the final image. The images could be cropped or altered in another way so that the edges if the image have a better quality. I have not done that with these sample images yet. The sample images do clearly show that the dolly can be used with great success for other multi shot techniques than time-lapse sequences. Watch this blog, one of the next stories will be about HDR time-lapse sequences in combination with the dolly.