[RASMB] Dark interference fringe pattern

[Walter Stafford]

Hi Arne,

I would agree with Tom. The image on the camera needs to moved up to 
center the fringe pattern by adjusting the mirror at the bottom back end 
of the "downspout". There is a cover that can be unscrewed to expose the 
adjusting screws. Unfortunately the adjustments are not orthogonal; so 
you'll have to fiddle with both screws and you will probably have to 
adjust the rotational orientation of the camera head to re-level the 
fringe pattern before you are done. and re-do the radial calibration, as 
Tom mentioned.  If the image you show is not the zero order diffraction 
pattern, you will have to adjust it either up or down by a lot more to 
get to the zero order pattern. If you are not using interference window 
holders, the fringes should be very bright and somewhat overexposed if 
you set the window to 1.0 degrees or bigger. If not, then you probably 
do not have the zero order diffraction pattern in the camera. I have 
seen two machines fresh from the factory that were mis-aligned in this 
way. But luckily it's easy to fix.

Walter

Tom Laue wrote:
> Hi Arne-
> My guess is that the bottom optical track is out of alignment and that 
> you are looking at the first order diffraction image. Have your 
> service man (or do it yourself) align the bottom track mirror (on the 
> left hand end) to get the central envelop on your camera. You will 
> then need to re-do the radial calibration. The total time to do this 
> should be ~30 minutes.
> Best wishes,
> Tom
>
> Rufer, Arne wrote:
>> Dear colleagues,
>>
>> we recently encounter problems with the interference optical system 
>> on our XLI (upgraded to Proteome Lab version) in that the fringe 
>> pattern looks very dark (please see attached screenshots). Beckman 
>> field service recommended to us to clean the lenses in the laser 
>> housing of the monochomator arm (which we did paying attention to 
>> reinstall the lens in the correct orientation) and to clean/exchange 
>> the filter above the condensor lens. While intermittantly the 
>> brightness/contrast of the fringe pattern improved, we are back to 
>> "very dark" after trying to further clean things up. What remains 
>> also is a concentric interference pattern superimposed to the 
>> expected fringes, which you can see on the left side of the fringe 
>> patttern in the second screen shot. This ghost pattern is also 
>> visible when we look at the scallop position or an empty cell hole.
>> Any suggestion as to how we can get our machine back to normal would 
>> be greatly apprecieated.
>>
>> Best regards,
>>
>> Arne
>>
>>
>>
>>
>>
>>
>>
>> Dr. Arne Rufer
>> F. Hoffmann-La Roche AG
>> PROBMO Optical Spectroscopy
>> 065/207
>> CH-4070 Basel
>> Tel: 0041-(0)61-6882126
>> arne.rufer at roche.com <mailto:arne.rufer at roche.com>
>>
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>

-- 
Walter F. Stafford, Ph.D.
Senior Scientist
Boston Biomedical Research Institute
64 Grove Street
Watertown, MA 02472
617-658-7808