PS CS6: Align layers -- Layers do not overlap enough error?

[Bob_B]

I've been practicing macro focus stacking techniques in studio lately, and ran into what I consider to be a strange error when aligning layers in photoshop CS6. The setup: Canon 7D with EF 100 mm f/2.8L macro on a firm,stable tripod imaging a stable metal rod with a bit of corrosion. I use a macro focusing rail (Really Right Stuff) to move the camera:lens through the focal field. I shot 13 photos, which I imported into LR 5.7 and edited as layers in PS. I've done this many times in past without incidence. However, with this series of 13*, when I select all 13 layers and click auto-align layers, using the default 'auto' projection, I get an error: "Layers do not overlap enough to detect alignment. In general, images intended for alignment should overlap by approximately 40%." These layers, I assure you, are nearly perfectly aligned going into PS. In fact, if I simply go ahead and stack them in PS (without the auto-align step), I get a very reasonable focus stack, with no discernible imaging errors. The same set of images create no issues in Zerene Stacker, and other images shot at the same time, but of different and more complex subjects (flyfishing flies), aligned without error in PS CS6.

Thus, my question: Why is PS CS6 upset about this group of nearly-perfectly aligned images? I ask simply to learn and understand the limitations of photoshop. I have alternative means to deal with PS stacking problems, ie., Zerene Stacker.

Thanks for your time and replies,

   Bob

* I should note that a second set of 9 images of the same subject also caused the error. It seems that the subject (= simple metal rod) is a common feature that causes this error.

[Bart_van_der_Wolf]

Thus, my question: Why is PS CS6 upset about this group of nearly-perfectly aligned images? I ask simply to learn and understand the limitations of photoshop. I have alternative means to deal with PS stacking problems, ie., Zerene Stacker.

Hi Bob,

No explanation, it's a mystery. The only thing I can think of is that the focus step interval is maybe too large for Photoshop to determine matching features? Maybe the corrosion or the edges of the rod are not distinct enough to be seen as detail that needs alignment? Just guessing.

Other than that, it demonstrates the benefit of a dedicate application for such special tasks. Photoshop offers nothing to help finish the task, there are no manual controls. When it works automatically, fine, but if it doesn't work, you're out of luck.

Cheers,
Bart

[Bob_B]

Thanks Bart. Regarding the focus step size, very small: approx. 0.75 to 1.0 mm between steps as measured on the scale provided by the RRS macro rail. My best guess on what caused this error is not enough difference between images. The rod was only ca. 8-9 mm, so there was a lot of overlap in focus. No matter, as you say, use the right tool (in this case Zerene) and the job gets done.

   Bob