Stacking from ordinary (not post focus) videos

Started Oct 28, 2019 | Discussions thread
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gardenersassistant Veteran Member • Posts: 7,699
Stacking from ordinary (not post focus) videos

Mainly for close-ups of flowers etc I use Panasonic's post focus to capture videos from which I can extract JPEGs to stack. This sort of thing.

Stack of 23 JPEGs extracted from a 6K post focus video.

Post focus racks the focus from the front to the back of the scene while the video is captured. In this post the question arose of whether it would be possible to do this with a camera that does not have post focus. So I did an experiment.

Here is an image captured at f/2.8. The flower towards the bottom left is in front of the plane of focus and the flower towards the upper right is behind the plane of focus.

It is only at around f/16 that both of these flowers come fully into focus, by which point the background has become quite intrusive. Also, with the minimum shutter speed set to 1/80 sec, the ISO had risen to ISO 2000.

I then captured a 30 fps 6K post focus video, hand-held. The capture took 4 seconds. As you can see from the video here at Flickr , there was a little subject movement. With the aperture set to f/2.8 and using auto ISO, the camera used base ISO 200 with shutter speed 1/200 sec.

Using Helicon Focus I stacked 47 JPEGs extracted from the video and did one tiny dab of retouching. This produced a TIFF which I processed mildly in Lightroom, to produce this 1300 pixel high image (1300 pixels high is my normal output size). It is uncropped, in the camera's native 4:3 aspect ratio.

I then set the camera to video mode. 6K is not available and so I had to use 4K, and had to use a 16:9 aspect ratio. I accidentally used 25 fps rather than 30 fps. I put the camera in manual focus mode and with the focus fixed I captured a video as I moved the camera, hand-held, so the focus moved from in front of the nearest flower to behind the furthest flower.

Not having done this before I didn't know how fast to move the camera. In the event the capture took 13 seconds. As you can see from the video here at Flickr, there was some quite large hand movement and possibly more subject movement than with the post focus capture. Even if the subject movement was not greater in size, it was certainly much longer in time while the relevant part of the scene was being captured, giving more opportunity for the movement to create problems.

With the aperture at f/2.8 and using auto ISO, the camera used ISO 250 with shutter speed 1/250 sec. (Given the 1/80 sec minimum shutter speed setting, I don't know why the camera raised the ISO.)

Using Helicon Focus I stacked 162 JPEGs extracted from the video. I retouched half a dozen or more edges. This produced a TIFF which I processed mildly in Lightroom, to produce this 1300 pixel high image.

Here is the 6K post focus stack cropped to the same 16:9 aspect ratio.

There are several stacking issues here. Hand movement is not necessarily problematic given suitable stacking software. However, the flowers were moving relative to one another, and overlapping, both of which can cause stacking problems. This was presumably worse for the 4K video because of the much longer duration. With more experience I imagine a much shorter duration could be used.

Relative movement would not be an issue in calmer conditions, but the overlapping issue would. (Where two areas overlap and both are required in focus, there will be a halo around the edge of the nearer area, and the greater the front to back distance between the areas, the worse the halo will be.) This problem arises whatever capture method is used (video or stills).

Especially given that this was not an entirely straightforward scene and conditions, and I have no prior experience with the technique, this experiment suggests to me that stacking from video can be a practical proposition for non-post focus videos.

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