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focus stack: fuzzy transitions

Forum|Forum|8 years ago
December 22, 2017
3 replies
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I have a shot with some columns very close (50cm away?) and sky background at infinity focus. I have a two-shot focus stack, one for the columns and one for the infinity-focused sky.

The problem is, the transition between the two is rather harsh. And the unfocused areas of one bleeds into the other. Is there any way I can fix this?

Or should I have shot it differently? I'm not sure how shooting more shots in the focus stack would help, since there's nothing to focus on in between the sky and the columns.

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Correct answer D Fosse

Yes, this can be a problem. Photoshop's Auto-Blend algorithm still has some shortcomings.

What I always do is duplicate the relevant layers after the Auto Align, so that I can use them to later paint in these fuzzy areas if needed.

There is specialized stacking software that supposedly does better. I haven't tried any of them, but Helicon Focus seems to come highly recommended everywhere. It's not free, though.

Norman Sanders

Legend

At this point, with the photographs already shot, the following suggestion is offered in the event you run into a similar situation in the future. I believe if the sky shot was focused on the hyperfocal distance rather than infinity, chances are the near (burred) elements in that sky shot would be far less fuzzy. Here goes:

When a lens is focused at Infinity, the depth of field extends from infinity to some point nearer the camera. If the lens is focused on that near point (the hyperfocal distance) the depth of field extends from half the hyperfocal distance to infinity and the wall/columns in the sky shot would be less blurred. That would make the composite image easier to handle. How much of an improvement?

That depends: Since hyperfocal distance is affected by lens focal length and f/stop (which we don’t know) there is no way of predicting, how much this would have helped. But, for what it’s worth, working without that specific information, it is likely that if you shot more exposures of the sky, at a variety of distances less than infinity, one or more of them would have been recognizably better that the current one.

D Fosse

Community Expert

Yes, Norman, that's how we all used to work. Depending on the camera in question, however, this ancient wisdom may no longer be valid.

The fact is that with the new 36 - 50 MP sensors, and a modern lens to match, there is no longer such a thing as "depth of field". You can zoom in to pixel level and discover that the plane of critical focus is in fact thin as a sheet of paper. Everything behind and in front of that thin plane is...well, out of focus. This is true even for a 24 mm wide angle lens.

Few people realize how little resolution you actually had with film, compared to modern sensors, until they see it demonstrated. And the lenses have followed suit. I have tried a couple of the old manual Nikkors on my D800, and not one of them is even close to the contemporary versions.

It changed my habits profoundly. I used to generally focus 1/3 in (if not hyperfocal) - which used to bring everything important into focus. That's no longer so. Today I need to pick critical focus point with extreme care, because I have to stand by it. I need to be able to explain why that is in focus and this is not.

All that said - a couple more frames here would certainly have helped.

Chuck Uebele

Community Expert

A lot of that is just due to optics, as there is either a blurred area by the bg or by the foreground that overlap without any in focus detail in those areas. PS does have it's shortcomings with stacking. I've found Zerene Stacker does a better job with some soft areas that PS seems to produce.

D Fosse

Correct answer

Community Expert

Yes, this can be a problem. Photoshop's Auto-Blend algorithm still has some shortcomings.

What I always do is duplicate the relevant layers after the Auto Align, so that I can use them to later paint in these fuzzy areas if needed.

There is specialized stacking software that supposedly does better. I haven't tried any of them, but Helicon Focus seems to come highly recommended everywhere. It's not free, though.

H

hhost05Author

Known Participant

The thing is, I wasn't using a focus stacking software like PS's blend mode.

Instead, I just aligned the images in PS. Then I blended them manually using masks. I included the 3rd image to show the trouble. The fuzziness of the bottom image cannot be completely "covered" by the clear and in-focus image of the top part. The part of the "fuzzy" image that isn't covered by in-focus image is what creates the halo in the combined image.

D Fosse

Community Expert

OK. If you already have a mask the job is done. That's what takes time, the rest is easy. The quick'n'dirty solution then is to just use the clone stamp.

But what I would do is divide the background in three, one part for each window, and then shrink the foreground layer just enough. Realign the background for each window.

Since you haven't tried it, you could give Auto Blend a shot.

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