Mysterious rings on Hasselblad viewfinder

When using my Hasselblad 501CM in quite heavy rain and wind the other day, after about two hours I noticed these mysterious rings appearing on the Acutte Matt D viewfinder.

Once the Blad had tried out, they dissapeared.

What are they, and do I need to worry about it? Obviously a cause of the wet, but quite odd how they are perfectly circular and cylindrical. I assume they won't impact the image on film as the picture goes out the back through the curtains.

You probably got a drop of water between the screen and the Fresnel. Once in there capillary action pulled it around.
That's my guess, anyway.
No it won't affect the image. If everything is dry there probably won't be a lasting problem. I would probably remove the screen and make sure it doesn't have any lingering moisture either on or around it.

Yeah, I took your advice and took the screen out just now to clean it and dry it (never done that before - didn't realise it was so easy!).

What I noticed is that really faint circular rings could be seen - almost opaque against the glass, so I think when it gets wet, the magnification distance to the mirrors emphasises them to make them as visible as they were in the screenshots above.

ted_smith said:

Yeah, I took your advice and took the screen out just now to clean it and dry it (never done that before - didn't realise it was so easy!).

What I noticed is that really faint circular rings could be seen - almost opaque against the glass, so I think when it gets wet, the magnification distance to the mirrors emphasises them to make them as visible as they were in the screenshots above.

Click to expand...

Ted:

Google "fresnel" and consider "faint circular rings"