[RASMB] "wavy" interference optics residuals

[Tom Laue]

Hi Debbie-
Sorry for the delayed response, but I just returned from meetings.
One possible cause for your observations is if the image is overexposed 
(dark dark and bright white fringes). If the fringe images are of 
too-high contrast, then the Fourier transform will oscillate around the 
correct fringe displacement rather than track it exactly. The tell-tale 
for this problem is if the periodicity of the oscillations is a multiple 
(1, 2, 3...) of the fringe displacement (e.g. do the oscillations 
increase in frequency in regions with steep gradients).
The fringe image should look sort of "washed out" by eye, while 
maintaining a good image of the fringes. Jeff Lary 
(jeffrey.lary at uconn.edu) at UConn has a very nice tutorial on how to set 
the exposure for the interferometer.
Best wishes,
Tom

Debbie Eckert wrote:
>
> Hi All,
>
> We have been experiencing a problem with our interference data in 
> which after data fitting, the residuals frequently have a systematic 
> “wavy” look to them where they rise above and below zero multiple 
> times >7 across the fitted data. Subtracting a water blank does not 
> fix the problem, and it has occurred an several different samples. In 
> real time, the fringes also “jump” during centrifugation. Is this an 
> indication of an equipment problem, perhaps that there is something 
> unstable in the centrifuge and/or optical system that is leading to 
> the movement of the fringe pattern detected by the camera? If so, is 
> there a likely culprit? If not, what is likely to cause this?
>
> Thanks for the help,
>
> Debra M. Eckert, Ph.D.
>
> Research Assistant Professor of Biochemistry
>
> University of Utah
>
> deckert at biochem.utah.edu
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> RASMB mailing list
> RASMB at rasmb.bbri.org
> http://rasmb.bbri.org/mailman/listinfo/rasmb
>   

-- 
Department of Biochemistry and Molecular Biology
University of New Hampshire
Durham, NH 03824-3544
Phone: 603-862-2459
FAX:   603-862-0031
E-mail: Tom.Laue at unh.edu
www.bitc.unh.edu
www.camis.unh.edu