Last updated: 2020-10-19

Photo Stacking... what is it?

Photos have a limited depth of field beyond which the image is out of focus. Focus bracketing is the technique of taking multiple photos in rapid succession with different focus. Photo stacking means to then merge all the areas that are sharpest to create a single image with a much wider depth of field, yet that picture will retain the same bokeh for what lies beyond.

My new OMD E-M1 II Olympus camera has automated photo bracketing and stacking capability when using compatible auto-focus lenses. None of my other cameras have ever offered either of these facility.

unstacked single image
stacked multiple image

Above is one of the first images I took. On the left is one of the bracketed set and on the right is photo-stacked image merged automatically by the camera firmware. The most important difference is the improved depth of field. There is also a color difference, but that is because I took the unstacked image from the raw image file, that had no white ballance, or other processing applied, while the stacked image is obviously entirely processed by the camera's internal firmware, by whaterever settings it had defaulted to.

No raw file exists for the stacked image, thus the most prominent caveat I learn is that the camera rendered the result using the reduced "thumb nail" resolution that I have for jpg results. I normally work with the raw file. I also notice that the bracketing steps were too big making most of the pictures in the set out of focus and no doubt excluded from contributing to the stacked image. I will have to experiment with different settings and so I configure camera custom setting C3 for stacked macro photography:

custom settings
9 shots
Thus a total of 10 per set makes it easier to recognize the set.
LF no raw
Large image, fine resolution to produce a decent quality stacked image. I decided not to waste space with all the individual raw images
File name C3__
identify macro bracketed sets
Static Focus + manual
not continuous, allow easy adjust of initial setting

My next attempt explores focal depth with a trumpet shaped flower.

first in set, I should have chosen the closest point
last in set has gone down the trumpet, not so interesting
stacked result

These tall flowers wave in the slightest breeze and so I felt wide aperture short time interval would give the best stacked result, but now I'm wondering, how does this compare with simply setting a much smaller aperture and not bothering with stacking?

stacked 8x shutter 5000
unstacked 1x shutter 500

As expected the slight crop that is introduced by the stacking algorithm is apparant, also the greater blur on what is outside the focus bracketing range. As these two would have had similar exposure durations (the time for focus bracketing steps is unknown) it's only a hint about the merit of either. I took a few more pictures but nothing noteworthy. I did see some replication from the merging of multiple images where there had been motion, like the seed in the bottom left here.

Next I want to look at bracketing step sizes and doing larger objects from further away, maybe even with a telephoto lens. Meanwhile click the icon to see some very inspiring work by Peter Baumgarten.