Not sure about the rainbow, sure you don't have any light leaks? Could be a sliver, diffracting, but seems unlikely. Were they both with the same lens?
Up to you about the Contina, I can fix it on X only and put it back together, you'd have to figure out a viewfinder, but you could attach an accessory rangefinder and use that, or there are some accessory viewfinders, and figure out who good the coverage is. If you want to then put the plate in the post, if not I'll just put it to one side.
Any scores at the flea market?
Flickr group - thanks. Might see if someone could date the film. I scanned a few from the Pentax:
Tilly by
John Rodriguez, on Flickr
Swing2 by
John Rodriguez, on Flickr
Ana in furs by
John Rodriguez, on Flickr
The last one really shows the bokeh of this lens, i.e. how it renders the out-of-focus bits. Actually looks loads better on the print, seems to have gone a bit blurry(er). The large aperture enabled me to get pics I wouldn't normally be able to - the dog was at 1/30th, if this were f2.8 it'd be a shutter speed of 1/4 and I'd need a tripod and a miracle.
My wife suggested using our ipad as a light box so I managed some less-crap scans of the Verichrome. It confirmed really what I knew, the reciprocity failure went up enormously and only a few are worth printing. Will get them done in due course though. I don't bother with post-processing so don't really need a negative scanner, I guess it's not so good at print scanning either though even at 1200dpi so maybe I'll think about it for Christmas!