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1

Photoshop Auto Align function for focus stacking

Explorer ,
Dec 14, 2022 Dec 14, 2022

When using the Auto Align feature of Photoshop, is there a way to forbid the function from changing the geometry of the frames it is aligning?  

 

I use the Auto Align feature primarily for focus stacking product photos.  Is there a way to limit the function to only those transformations that preserve the geometry and aspect ratio of the layers?  This would help eliminate many problems where the align function gets confused. The function gets distracted by possible operations such as key-stoning and stretching corners, which are never valid solutions to my alignment needs.  

 

Please see an example of an error in my screenshots.

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Adobe
Community Expert ,
Dec 14, 2022 Dec 14, 2022

For this purpose you definitely don’t want to leave Photomerge on Auto. Try selecting the Reposition option or maybe Collage; according to the Create panoramic images with Photomerge topic in Photoshop online help, these are the descriptions for those options:

 

quote
  • Collage Aligns the layers and matches overlapping content and transforms (rotate or scale) any of the source layers.
  • Reposition Aligns the layers and matches overlapping content, but does not transform (stretch or skew) any of the source layers.

 

Most of the other options distort because the more common cases for panoramas (e.g., landscape photography) look best with some kind of projection (such as spherical) that requires altering the geometry of each source image, so Auto tends to pick an option that does that. Collage and Reposition are for things like merging multiple scans of a big flat printed piece, so they don’t distort.

 

In other words, if I understand Reposition correctly, that option means “just move it” — no other changes to each layer.

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Explorer ,
Dec 23, 2022 Dec 23, 2022

I worry that I'm left choosing between the software not correcting for the fact that the image size changes as you rack focus through a focus stack - or it continuting to bend the edges in ways that aren't rectangular... I'll give it a try and let you know. 

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Community Expert ,
Dec 23, 2022 Dec 23, 2022

Lens barrel focusing is always a bit risky for this, because the lens optical center moves by quite a substantial distance, and so it changes the actual viewpoint along the axis. The safest way is to focus by just moving the camera body with the lens absolutely fixed (using bellows and focusing rail). If that's not possible, moving the camera body and lens together - without moving the focusing ring on the lens - is the next best. The optical travel is still much less than with the lens barrel alone.

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Explorer ,
Jan 23, 2023 Jan 23, 2023

I never thought of this solution; I don't currently have a slider that will allow me to test your idea, but I hope to get to test this out soon.  I will let you know.  

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New Here ,
Jul 18, 2024 Jul 18, 2024

Won't that change the size of the image the lens projects on the sensor. You still have the problem. In fact I suspect this option will increase the size of the problem.

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Community Expert ,
Jul 18, 2024 Jul 18, 2024

Size isn't a problem; the moving viewpoint is.

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New Here ,
Jul 18, 2024 Jul 18, 2024

Using a bellows like this will essentially be changing the focal length of the lens. Are you saying that Photoshop can manage this mismatch of size in aligning images. How much difference can it manage.

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Community Expert ,
Jul 18, 2024 Jul 18, 2024
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Auto-align will handle size differences with no problem, probably as far as 2x or 3x.

 

All macro lenses change focal length as you move closer. I once read that a Micro-Nikkor 60/2.8 at close focus is actually 35mm focal length.

 

That probably happens generally in most lenses, but with a standard (non-macro) focusing range it's not significant.

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