Are there any very slow (ISO 6 or 12.5) medium format films availiable?

Stacking filters tends to cause vignetting with some lenses. I often shoot in situations where a 400 speed film is too fast for the available shutter speeds on my camera. But I will not convince anyone that there is a reason to want to pull films as I'm clearly wrong. Lets figure out how to make the OP change his question so we can talk about something else.

Tech Pan was available in 120 and is still available on ebay and elsewhere. Normal rating of 25, and with age shooting it at 12 might be about right.

Punker said:

Sorry I was referring to paper negatives.

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No "sorry" required. It was my fault in fact for making a false connection between a previous post (#11 ) which referred to Pan F in another context and then your post 12 which was in response to another post. It would have become quite clear if I had taken the time to read the quote in your post to which you were replying.

pentaxuser

Since you mentioned fine-grain, this suggestion is probably not what you're after, but it bears mentioning that Rollei IR 400/Superpan 200/Retro 400s are exposed at an EI of about 3 to 12 when shot through Hoya R72 filter or equivalent (IR pass 720 nm.) Available in medium format.

iandvaag said:

Since you mentioned fine-grain, this suggestion is probably not what you're after, but it bears mentioning that Rollei IR 400/Superpan 200/Retro 400s are exposed at an EI of about 3 to 12 when shot through Hoya R72 filter or equivalent (IR pass 720 nm.) Available in medium format.

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Fomapan 400 as well. Beautiful results.