This weeks digital task was to create an image that was sharp from front to back using a technique called focus stacking. Following guidance in an on-line tutorial by Gavin Hoey the basic technique is to take multiple images with a tripod mounted camera changing only the focus and then combining (stacking) the images in Photoshop by using the auto-blend function to create a combined image that automatically extracts the sharply focussed area of each image to create a single uniformly sharp image.
A day trip to Hayling Island provided an ideal opportunity for some land and seascape shots to practice the technique. The images above are the first and last in a series of 4 used to create a final combined image clearly showing the different points of focus.
Care needs to be taken in creating the images to ensure there is minimal movement of the camera between images to ensure they stack as cleanly as possible, this was difficult on the day as although the weather was bright it was extremely windy. This can be offset to some degree using the auto align option in the “stack images” function but obviously the better the in camera alignment the better the final result.
The process is to open all the images required, then make any individual adjustments as normal post processing, using the “stack images” function a new file is created with each of the images on a separate layer. Then to automatically mask and create a combined image simply select all the image layers and then “auto-blend layers” from the edit menu. There are no user options for the part of the process it is completely automatic.
The resulting image has some issues e.g. around the 50p piece for example there are some aberrations, I think this is due to the movement of the waves behind the 50p across the various images and the focus distance “jump” between the groyne the 50p is standing on and the beach area which is probably at least 20 metres behind it, indicating that such images need to be created from a scene where is a continuous scene i.e. the focus gradually and continuously changes.
A second series also resulted in some serious issues with the final image again I believe caused by movement in the scene i.e. in upper left area of sky and waters edge as the static part of the image – the line of wooden posts the processing has worked well. The prevailing weather conditions were extremely windy which caused the clouds to be moving at speed and casting moving shadows on the beach.
Final Image 2nd Series
I was able to improve the result by manually masking the last image i.e. the one with the furthest focus distance and obtain an acceptable image. This experience leads me to conclude that this technique is best suited to relatively static scenes with consistent lighting and continuity of focus and hence I can understand the appeal of this technique for macro subjects.
I decided to try the technique with more static scenes and on a visit to Lyme House Park a National Trust property in Cheshire I took a series of images of the house and some landscape scenes which I believe are far more successful at demonstrating the technique than my previous attempt.
A different view, made from 5 images starting with the foreground grass and ending with the house. I manually adjusted the masking on this image to exclude some distracting figures on the path which appeared twice in different positions between exposures, lastly I selectively applied a high pass filter to the house and a graduated filter to the sky.
Finally the same scene and technique shot in infra red. There is a slight difference in the scene due to the difference between the full frame Canon 5D and the crop sensor IR modified Canon 40D.