In this photograph, which is a 4-layer stack of just the central area, I left the front & back soft intentionally.
It has quite a strong area of what I can only call 'vertical chromatic aberration' at the back right, where the least in-focus area is.
Reading other questions makes me think the term for this is Longitudinal (axial) chromatic aberration. Please correct me if I'm wrong.
So, I have two linked questions, one objective, the other subordinate question [I'm afraid] more subjective. The second couldn't stand alone, so I'm sneaking it in & hope I don't bring down the wrath of the opinion-based close voters.
What caused this & can it be fixed?
Is it caused by my admittedly cheap lens just not being up to the task, or it it because the backlight is actually being diffracted as it hits the petal edge?
Photoshop's defringing doesn't seem to want to touch it because it's not lateral. Is there a suitable tool in Photoshop I've not yet found?
I could paint it out by hand, but I'm not certain I actually want to, which brings me to the subjective question...
Should I just leave it as it is? Does it work? Is it 'art' or a 'mistake'?
...or more objectively - do other photographers use this as a technique in itself, or do they take great pains to avoid it, even in intentionally soft-focus areas?
Is it, in effect 'colour bokeh'?
Additional information from comments, which helped towards the accepted answer...
How was the image sharpened? What happens to this effect if the overall sharpening settings are reduced?
It was sharpened with a high-pass overlay, but the softer edges are painted out of the high-pass manually, so there is no sharpening at the problem area. Each layer of the stack shows the same effect, lessening as that area gets closer to focus. Had I done 2 or 3 more layers to get the entire thing in focus, as I normally do, it would have disappeared; so it's an effect of the out-of-focus itself.
Nikon D5500 Tamron 70-300mm f4-5.6
300mm ISO 100 1/200 @f5.6
From similar questions - predominantly Photographic techniques to avoid chromatic aberration?
I can't avoid the contrast between foreground & background, the composition is dependant on the juxtaposition.
This is already a crop of a larger shot, but the aberration appears unchanged as the lens centre is approached.
Stopping down for this particular style leaves the front & back too sharp & also starts to kill the vignette background & make the actual shapes too visible; I do stop down if I need sharp right the way through, but there's something about focus-stacking with the lens wide open that I particularly like.
Is the only real answer, "Get a dedicated macro lens." ?