Stains on c41 film

[Benchat]

Hello,
I've been having some repeated stains on 4x5 sheets that I have given to develop, that I then scan.
Given that it looks like chemical stains I thought it was an issue to do with processing.
The lab who does it having no explanation, I have given them to another lab and had the same issues.
Since it doesn't happen all time but is almost always visible on uniforme skys or surfaces I wonder if it has something to do with the way I expose the film. A problem possibly made made visible once I scan the negative. Its Portra 160 and 400, overexposed a third of a stop. I have joined an image. Note that I have put a curve to better show the problem.
190039
If anyone would have an explanation or has had same problems I would be very grateful to hear from you.
Cheers,
Ben

[koraks]

It looks like insufficient agitation or insufficient bleaching or fixing to me. I'd try re-bleaching and fixing to see if that solves the issue. If it doesn't, it's a problem related to the color development step.

[agregov]

I doubt this is a processing or chemistry issue given two pro labs display the same issues. Is this new film or old? Did the film go through an X-ray scanner? Are you using a modern multi coated lens? Are the film holders light tight? Is your scanner clean? An easy way to test is you could reshoot some images with a new box of film (I'd order from B&H where you know it won’t be old), send it to a pro lab you know does solid work and have them scan the negs. If the negs still exhibits the same issue, you need start looking at your equipment/workflow. If the negs and scans are clean, it was likely your film.

[Benchat]

Thank you both for your help,
The film is new and has not been through X-ray. The scanner is new and I have scanned the film with another scanner so I'm positive it's on the negative.
However if it would be the lens (Rodenstock APO Sironar N 150mm f5,6) would I not see the same stains on the whole set of negatives? Could I see this on the lens itself?
The film holders I'm not a 100% sure about. But I use 6 filmholders and it seems to be though out the whole lot. I have in the meantime changed camera so I'll see if it was a light leak in the camara.

[Joe O'Hara]

Benchat, FWIW, I had a similar problem trying to develop Ektar 100 in a Jobo tank in a controlled temperature bath, without the processing machine. The development step is so short (3:15) that it is easy to imagine that small errors the color development step could lead to staining.

It does not look like fog from the camera or film holders (most likely would look white) or a lens problem to me. Was it really completely dark where the film holders were loaded?

Despite the fact that you sent the films to two different labs and saw the same problem, I wonder how much C41 those labs are doing these days. I would not rule out processing as being the cause.

I gave up trying to develop what little Ektar I use and send it out to Praus Productions instead. I never had a problem with their work.

[Benchat]

Thank you for your feedback. The lab only does c41 and has only ever done that. But it doesn't of course rule it out. The film have been loaded in the dark.
I'm working on a project in Jordan, and will have more film to process in 2 months so I'll keep everyone posted if it still occurs.

[blue4130]

Its a long shot, but I seem to recall toyo? holders having an issue with the darkslides not being truly opaque and the result looks quite similar to this.

[koraks]

Good catch Vance. It does look like it.