[RASMB] Interference:ddH20 shows fringes?

[Troy Sorensen]

I am trying to perform sedimentation velocity with interference optics on an
XL-I.  I have tried to perform a blank scan on the cell I am using (3 mm
centerpiece with sapphire lenses) with ddH2O.  Should I being seeing fringes
with ddH2O?  At 45K, 25C I see fringes on the left and right side of the
meniscus and towards the bottom of the cell.  However, if I lower the
contrast from 105 to ~80 I can see fringes across the whole cell?
Also if I spin at only 3K I see an even fringe display from top to bottom.
 Can you explain why there is difference in fringe display at high and low
speeds and if I should be seeing fringes with pure water?
My experience level with the set-up of interference optics is pretty low so
any additional advice would be greatly appreciated.
Thanks,
Troy
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://list.rasmb.org/pipermail/rasmb-rasmb.org/attachments/20090616/fb69e56a/attachment.htm>