Finally got round to scanning the negs from my little Isolette, and it looks like it's leaking. These are just snapshots to test the cam, is it possible to patch it up or will it need another set of bellows? Cost me £5, so it's no great loss, but it is a nice funky little cam. **edit** I think I posted this in the wrong forum - trust me eh.
Looks to me like it is not leaking from the bellows but rather from the film window in the back, or that your 120 film was not wound tightly on the spool.
A light leak in the bellows would show up very white and be way overblown. This looks more like a subtle light leak that sneaks it way through the film window or comes from loose film on the take up reel. If I were to guess I would look at the take up reel. I have several old AGFA cams, Clicks, Clacks, and Isolas and if the take up reel is loose and I change the film in bright light I get a similar result. So now I only open up the camera in the dark and then I wrap up the film in aluminum foil. When I do that I do not have these problems.
Cheers, I'll give that a go - there's a roll of velvia in it at the moment, so I'll finish it off today and take extra care and then see if the problem is still there.
FWIW I have had exactly that with my Rollei TLR and it was me fogging the film by loading in daylight. Makes it look kind of milky normally... When I have had light leaks in MF cameras, as Wally says, it's much more consistent and sharper and brighter. Rob