Will changing subject size when using a focus rail affect focus stacking?
Asked 9/3/2022
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I’m experimenting with focus stacking using a rail to move the camera toward and away from the subject. In my first test, moving the camera across the subject made the subject appear larger in the closer frames, even though the images were otherwise scaled the same.
Will this magnification change cause problems for typical focus-stacking software? Should I try to minimize it by moving farther away, or by adjusting zoom to keep the subject the same size? Or is it better to keep the camera in one place and change focus instead?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
3y ago
2 Answers
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Taking the images for focus stacking by shifting the camera position, or by shifting the focus distance, both cause a change in the size of the subject.
Because the maximum magnification only occurs at the minimum focus distance, there really is no way of avoiding this issue and it is expected... it should not confuse the focus stacking algorithm. But if you only used the first and last images of the sequence it might (you might need to scale the images separately/differently before stacking).
Originally by user70370. Source · Licensed CC BY-SA 4.0
user70370
3y ago
0
Generated from our catalog & community — verify before relying on it.
A size change between frames is normal in focus stacking. Whether you move the camera on a rail or change focus with the lens, magnification usually changes somewhat, especially at close distances, and stacking software can often handle small differences.
The bigger issue with moving the camera is parallax: shifting camera position changes perspective, which can create alignment problems that are harder to fix than simple scaling. So for most subjects, it’s usually better to keep the camera position fixed and change focus rather than move the camera.
If your frames have slight magnification differences, alignment software can rescale them before stacking. Tools such as Hugin’s align_image_stack can help with this, and Enfuse can be used for stacking.
So: no, the size change alone should not usually confuse a typical stacker, but moving the camera introduces perspective changes that can. If possible, keep distance constant and rack focus; use alignment to correct the smaller magnification changes that remain.
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